1	// SPDX-License-Identifier: GPL-2.0-or-later
2	/*
3	* Budget Fair Queueing (BFQ) I/O scheduler.
4	*
5	* Based on ideas and code from CFQ:
6	* Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
7	*
8	* Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
9	* Paolo Valente <paolo.valente@unimore.it>
10	*
11	* Copyright (C) 2010 Paolo Valente <paolo.valente@unimore.it>
12	* Arianna Avanzini <avanzini@google.com>
13	*
14	* Copyright (C) 2017 Paolo Valente <paolo.valente@linaro.org>
15	*
16	* BFQ is a proportional-share I/O scheduler, with some extra
17	* low-latency capabilities. BFQ also supports full hierarchical
18	* scheduling through cgroups. Next paragraphs provide an introduction
19	* on BFQ inner workings. Details on BFQ benefits, usage and
20	* limitations can be found in Documentation/block/bfq-iosched.rst.
21	*
22	* BFQ is a proportional-share storage-I/O scheduling algorithm based
23	* on the slice-by-slice service scheme of CFQ. But BFQ assigns
24	* budgets, measured in number of sectors, to processes instead of
25	* time slices. The device is not granted to the in-service process
26	* for a given time slice, but until it has exhausted its assigned
27	* budget. This change from the time to the service domain enables BFQ
28	* to distribute the device throughput among processes as desired,
29	* without any distortion due to throughput fluctuations, or to device
30	* internal queueing. BFQ uses an ad hoc internal scheduler, called
31	* B-WF2Q+, to schedule processes according to their budgets. More
32	* precisely, BFQ schedules queues associated with processes. Each
33	* process/queue is assigned a user-configurable weight, and B-WF2Q+
34	* guarantees that each queue receives a fraction of the throughput
35	* proportional to its weight. Thanks to the accurate policy of
36	* B-WF2Q+, BFQ can afford to assign high budgets to I/O-bound
37	* processes issuing sequential requests (to boost the throughput),
38	* and yet guarantee a low latency to interactive and soft real-time
39	* applications.
40	*
41	* In particular, to provide these low-latency guarantees, BFQ
42	* explicitly privileges the I/O of two classes of time-sensitive
43	* applications: interactive and soft real-time. In more detail, BFQ
44	* behaves this way if the low_latency parameter is set (default
45	* configuration). This feature enables BFQ to provide applications in
46	* these classes with a very low latency.
47	*
48	* To implement this feature, BFQ constantly tries to detect whether
49	* the I/O requests in a bfq_queue come from an interactive or a soft
50	* real-time application. For brevity, in these cases, the queue is
51	* said to be interactive or soft real-time. In both cases, BFQ
52	* privileges the service of the queue, over that of non-interactive
53	* and non-soft-real-time queues. This privileging is performed,
54	* mainly, by raising the weight of the queue. So, for brevity, we
55	* call just weight-raising periods the time periods during which a
56	* queue is privileged, because deemed interactive or soft real-time.
57	*
58	* The detection of soft real-time queues/applications is described in
59	* detail in the comments on the function
60	* bfq_bfqq_softrt_next_start. On the other hand, the detection of an
61	* interactive queue works as follows: a queue is deemed interactive
62	* if it is constantly non empty only for a limited time interval,
63	* after which it does become empty. The queue may be deemed
64	* interactive again (for a limited time), if it restarts being
65	* constantly non empty, provided that this happens only after the
66	* queue has remained empty for a given minimum idle time.
67	*
68	* By default, BFQ computes automatically the above maximum time
69	* interval, i.e., the time interval after which a constantly
70	* non-empty queue stops being deemed interactive. Since a queue is
71	* weight-raised while it is deemed interactive, this maximum time
72	* interval happens to coincide with the (maximum) duration of the
73	* weight-raising for interactive queues.
74	*
75	* Finally, BFQ also features additional heuristics for
76	* preserving both a low latency and a high throughput on NCQ-capable,
77	* rotational or flash-based devices, and to get the job done quickly
78	* for applications consisting in many I/O-bound processes.
79	*
80	* NOTE: if the main or only goal, with a given device, is to achieve
81	* the maximum-possible throughput at all times, then do switch off
82	* all low-latency heuristics for that device, by setting low_latency
83	* to 0.
84	*
85	* BFQ is described in [1], where also a reference to the initial,
86	* more theoretical paper on BFQ can be found. The interested reader
87	* can find in the latter paper full details on the main algorithm, as
88	* well as formulas of the guarantees and formal proofs of all the
89	* properties. With respect to the version of BFQ presented in these
90	* papers, this implementation adds a few more heuristics, such as the
91	* ones that guarantee a low latency to interactive and soft real-time
92	* applications, and a hierarchical extension based on H-WF2Q+.
93	*
94	* B-WF2Q+ is based on WF2Q+, which is described in [2], together with
95	* H-WF2Q+, while the augmented tree used here to implement B-WF2Q+
96	* with O(log N) complexity derives from the one introduced with EEVDF
97	* in [3].
98	*
99	* [1] P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O
100	* Scheduler", Proceedings of the First Workshop on Mobile System
101	* Technologies (MST-2015), May 2015.
102	* http://algogroup.unimore.it/people/paolo/disk_sched/mst-2015.pdf
103	*
104	* [2] Jon C.R. Bennett and H. Zhang, "Hierarchical Packet Fair Queueing
105	* Algorithms", IEEE/ACM Transactions on Networking, 5(5):675-689,
106	* Oct 1997.
107	*
108	* http://www.cs.cmu.edu/~hzhang/papers/TON-97-Oct.ps.gz
109	*
110	* [3] I. Stoica and H. Abdel-Wahab, "Earliest Eligible Virtual Deadline
111	* First: A Flexible and Accurate Mechanism for Proportional Share
112	* Resource Allocation", technical report.
113	*
114	* http://www.cs.berkeley.edu/~istoica/papers/eevdf-tr-95.pdf
115	*/
116	#include <linux/module.h>
117	#include <linux/slab.h>
118	#include <linux/blkdev.h>
119	#include <linux/cgroup.h>
120	#include <linux/ktime.h>
121	#include <linux/rbtree.h>
122	#include <linux/ioprio.h>
123	#include <linux/sbitmap.h>
124	#include <linux/delay.h>
125	#include <linux/backing-dev.h>
126
127	#include <trace/events/block.h>
128
129	#include "elevator.h"
130	#include "blk.h"
131	#include "blk-mq.h"
132	#include "blk-mq-sched.h"
133	#include "bfq-iosched.h"
134	#include "blk-wbt.h"
135
136	#define BFQ_BFQQ_FNS(name) \
137	void bfq_mark_bfqq_##name(struct bfq_queue *bfqq) \
138	{ \
139	__set_bit(BFQQF_##name, &(bfqq)->flags); \
140	} \
141	void bfq_clear_bfqq_##name(struct bfq_queue *bfqq) \
142	{ \
143	__clear_bit(BFQQF_##name, &(bfqq)->flags); \
144	} \
145	int bfq_bfqq_##name(const struct bfq_queue *bfqq) \
146	{ \
147	return test_bit(BFQQF_##name, &(bfqq)->flags); \
148	}
149
150	BFQ_BFQQ_FNS(just_created);
151	BFQ_BFQQ_FNS(busy);
152	BFQ_BFQQ_FNS(wait_request);
153	BFQ_BFQQ_FNS(non_blocking_wait_rq);
154	BFQ_BFQQ_FNS(fifo_expire);
155	BFQ_BFQQ_FNS(has_short_ttime);
156	BFQ_BFQQ_FNS(sync);
157	BFQ_BFQQ_FNS(IO_bound);
158	BFQ_BFQQ_FNS(in_large_burst);
159	BFQ_BFQQ_FNS(coop);
160	BFQ_BFQQ_FNS(split_coop);
161	BFQ_BFQQ_FNS(softrt_update);
162	#undef BFQ_BFQQ_FNS \
163
164	/* Expiration time of async (0) and sync (1) requests, in ns. */
165	static const u64 bfq_fifo_expire[2] = { NSEC_PER_SEC / 4, NSEC_PER_SEC / 8 };
166
167	/* Maximum backwards seek (magic number lifted from CFQ), in KiB. */
168	static const int bfq_back_max = 16 * 1024;
169
170	/* Penalty of a backwards seek, in number of sectors. */
171	static const int bfq_back_penalty = 2;
172
173	/* Idling period duration, in ns. */
174	static u64 bfq_slice_idle = NSEC_PER_SEC / 125;
175
176	/* Minimum number of assigned budgets for which stats are safe to compute. */
177	static const int bfq_stats_min_budgets = 194;
178
179	/* Default maximum budget values, in sectors and number of requests. */
180	static const int bfq_default_max_budget = 16 * 1024;
181
182	/*
183	* When a sync request is dispatched, the queue that contains that
184	* request, and all the ancestor entities of that queue, are charged
185	* with the number of sectors of the request. In contrast, if the
186	* request is async, then the queue and its ancestor entities are
187	* charged with the number of sectors of the request, multiplied by
188	* the factor below. This throttles the bandwidth for async I/O,
189	* w.r.t. to sync I/O, and it is done to counter the tendency of async
190	* writes to steal I/O throughput to reads.
191	*
192	* The current value of this parameter is the result of a tuning with
193	* several hardware and software configurations. We tried to find the
194	* lowest value for which writes do not cause noticeable problems to
195	* reads. In fact, the lower this parameter, the stabler I/O control,
196	* in the following respect. The lower this parameter is, the less
197	* the bandwidth enjoyed by a group decreases
198	* - when the group does writes, w.r.t. to when it does reads;
199	* - when other groups do reads, w.r.t. to when they do writes.
200	*/
201	static const int bfq_async_charge_factor = 3;
202
203	/* Default timeout values, in jiffies, approximating CFQ defaults. */
204	const int bfq_timeout = HZ / 8;
205
206	/*
207	* Time limit for merging (see comments in bfq_setup_cooperator). Set
208	* to the slowest value that, in our tests, proved to be effective in
209	* removing false positives, while not causing true positives to miss
210	* queue merging.
211	*
212	* As can be deduced from the low time limit below, queue merging, if
213	* successful, happens at the very beginning of the I/O of the involved
214	* cooperating processes, as a consequence of the arrival of the very
215	* first requests from each cooperator. After that, there is very
216	* little chance to find cooperators.
217	*/
218	static const unsigned long bfq_merge_time_limit = HZ/10;
219
220	static struct kmem_cache *bfq_pool;
221
222	/* Below this threshold (in ns), we consider thinktime immediate. */
223	#define BFQ_MIN_TT (2 * NSEC_PER_MSEC)
224
225	/* hw_tag detection: parallel requests threshold and min samples needed. */
226	#define BFQ_HW_QUEUE_THRESHOLD 3
227	#define BFQ_HW_QUEUE_SAMPLES 32
228
229	#define BFQQ_SEEK_THR (sector_t)(8 * 100)
230	#define BFQQ_SECT_THR_NONROT (sector_t)(2 * 32)
231	#define BFQ_RQ_SEEKY(bfqd, last_pos, rq) \
232	(get_sdist(last_pos, rq) > \
233	BFQQ_SEEK_THR && \
234	(!blk_queue_nonrot(bfqd->queue) || \
235	blk_rq_sectors(rq) < BFQQ_SECT_THR_NONROT))
236	#define BFQQ_CLOSE_THR (sector_t)(8 * 1024)
237	#define BFQQ_SEEKY(bfqq) (hweight32(bfqq->seek_history) > 19)
238	/*
239	* Sync random I/O is likely to be confused with soft real-time I/O,
240	* because it is characterized by limited throughput and apparently
241	* isochronous arrival pattern. To avoid false positives, queues
242	* containing only random (seeky) I/O are prevented from being tagged
243	* as soft real-time.
244	*/
245	#define BFQQ_TOTALLY_SEEKY(bfqq) (bfqq->seek_history == -1)
246
247	/* Min number of samples required to perform peak-rate update */
248	#define BFQ_RATE_MIN_SAMPLES 32
249	/* Min observation time interval required to perform a peak-rate update (ns) */
250	#define BFQ_RATE_MIN_INTERVAL (300*NSEC_PER_MSEC)
251	/* Target observation time interval for a peak-rate update (ns) */
252	#define BFQ_RATE_REF_INTERVAL NSEC_PER_SEC
253
254	/*
255	* Shift used for peak-rate fixed precision calculations.
256	* With
257	* - the current shift: 16 positions
258	* - the current type used to store rate: u32
259	* - the current unit of measure for rate: [sectors/usec], or, more precisely,
260	* [(sectors/usec) / 2^BFQ_RATE_SHIFT] to take into account the shift,
261	* the range of rates that can be stored is
262	* [1 / 2^BFQ_RATE_SHIFT, 2^(32 - BFQ_RATE_SHIFT)] sectors/usec =
263	* [1 / 2^16, 2^16] sectors/usec = [15e-6, 65536] sectors/usec =
264	* [15, 65G] sectors/sec
265	* Which, assuming a sector size of 512B, corresponds to a range of
266	* [7.5K, 33T] B/sec
267	*/
268	#define BFQ_RATE_SHIFT 16
269
270	/*
271	* When configured for computing the duration of the weight-raising
272	* for interactive queues automatically (see the comments at the
273	* beginning of this file), BFQ does it using the following formula:
274	* duration = (ref_rate / r) * ref_wr_duration,
275	* where r is the peak rate of the device, and ref_rate and
276	* ref_wr_duration are two reference parameters. In particular,
277	* ref_rate is the peak rate of the reference storage device (see
278	* below), and ref_wr_duration is about the maximum time needed, with
279	* BFQ and while reading two files in parallel, to load typical large
280	* applications on the reference device (see the comments on
281	* max_service_from_wr below, for more details on how ref_wr_duration
282	* is obtained). In practice, the slower/faster the device at hand
283	* is, the more/less it takes to load applications with respect to the
284	* reference device. Accordingly, the longer/shorter BFQ grants
285	* weight raising to interactive applications.
286	*
287	* BFQ uses two different reference pairs (ref_rate, ref_wr_duration),
288	* depending on whether the device is rotational or non-rotational.
289	*
290	* In the following definitions, ref_rate[0] and ref_wr_duration[0]
291	* are the reference values for a rotational device, whereas
292	* ref_rate[1] and ref_wr_duration[1] are the reference values for a
293	* non-rotational device. The reference rates are not the actual peak
294	* rates of the devices used as a reference, but slightly lower
295	* values. The reason for using slightly lower values is that the
296	* peak-rate estimator tends to yield slightly lower values than the
297	* actual peak rate (it can yield the actual peak rate only if there
298	* is only one process doing I/O, and the process does sequential
299	* I/O).
300	*
301	* The reference peak rates are measured in sectors/usec, left-shifted
302	* by BFQ_RATE_SHIFT.
303	*/
304	static int ref_rate[2] = {14000, 33000};
305	/*
306	* To improve readability, a conversion function is used to initialize
307	* the following array, which entails that the array can be
308	* initialized only in a function.
309	*/
310	static int ref_wr_duration[2];
311
312	/*
313	* BFQ uses the above-detailed, time-based weight-raising mechanism to
314	* privilege interactive tasks. This mechanism is vulnerable to the
315	* following false positives: I/O-bound applications that will go on
316	* doing I/O for much longer than the duration of weight
317	* raising. These applications have basically no benefit from being
318	* weight-raised at the beginning of their I/O. On the opposite end,
319	* while being weight-raised, these applications
320	* a) unjustly steal throughput to applications that may actually need
321	* low latency;
322	* b) make BFQ uselessly perform device idling; device idling results
323	* in loss of device throughput with most flash-based storage, and may
324	* increase latencies when used purposelessly.
325	*
326	* BFQ tries to reduce these problems, by adopting the following
327	* countermeasure. To introduce this countermeasure, we need first to
328	* finish explaining how the duration of weight-raising for
329	* interactive tasks is computed.
330	*
331	* For a bfq_queue deemed as interactive, the duration of weight
332	* raising is dynamically adjusted, as a function of the estimated
333	* peak rate of the device, so as to be equal to the time needed to
334	* execute the 'largest' interactive task we benchmarked so far. By
335	* largest task, we mean the task for which each involved process has
336	* to do more I/O than for any of the other tasks we benchmarked. This
337	* reference interactive task is the start-up of LibreOffice Writer,
338	* and in this task each process/bfq_queue needs to have at most ~110K
339	* sectors transferred.
340	*
341	* This last piece of information enables BFQ to reduce the actual
342	* duration of weight-raising for at least one class of I/O-bound
343	* applications: those doing sequential or quasi-sequential I/O. An
344	* example is file copy. In fact, once started, the main I/O-bound
345	* processes of these applications usually consume the above 110K
346	* sectors in much less time than the processes of an application that
347	* is starting, because these I/O-bound processes will greedily devote
348	* almost all their CPU cycles only to their target,
349	* throughput-friendly I/O operations. This is even more true if BFQ
350	* happens to be underestimating the device peak rate, and thus
351	* overestimating the duration of weight raising. But, according to
352	* our measurements, once transferred 110K sectors, these processes
353	* have no right to be weight-raised any longer.
354	*
355	* Basing on the last consideration, BFQ ends weight-raising for a
356	* bfq_queue if the latter happens to have received an amount of
357	* service at least equal to the following constant. The constant is
358	* set to slightly more than 110K, to have a minimum safety margin.
359	*
360	* This early ending of weight-raising reduces the amount of time
361	* during which interactive false positives cause the two problems
362	* described at the beginning of these comments.
363	*/
364	static const unsigned long max_service_from_wr = 120000;
365
366	/*
367	* Maximum time between the creation of two queues, for stable merge
368	* to be activated (in ms)
369	*/
370	static const unsigned long bfq_activation_stable_merging = 600;
371	/*
372	* Minimum time to be waited before evaluating delayed stable merge (in ms)
373	*/
374	static const unsigned long bfq_late_stable_merging = 600;
375
376	#define RQ_BIC(rq) ((struct bfq_io_cq *)((rq)->elv.priv[0]))
377	#define RQ_BFQQ(rq) ((rq)->elv.priv[1])
378
379	struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync,
380	unsigned int actuator_idx)
381	{
382	if (is_sync)
383	return bic->bfqq[1][actuator_idx];
384
385	return bic->bfqq[0][actuator_idx];
386	}
387
388	static void bfq_put_stable_ref(struct bfq_queue *bfqq);
389
390	void bic_set_bfqq(struct bfq_io_cq *bic,
391	struct bfq_queue *bfqq,
392	bool is_sync,
393	unsigned int actuator_idx)
394	{
395	struct bfq_queue *old_bfqq = bic->bfqq[is_sync][actuator_idx];
396
397	/*
398	* If bfqq != NULL, then a non-stable queue merge between
399	* bic->bfqq and bfqq is happening here. This causes troubles
400	* in the following case: bic->bfqq has also been scheduled
401	* for a possible stable merge with bic->stable_merge_bfqq,
402	* and bic->stable_merge_bfqq == bfqq happens to
403	* hold. Troubles occur because bfqq may then undergo a split,
404	* thereby becoming eligible for a stable merge. Yet, if
405	* bic->stable_merge_bfqq points exactly to bfqq, then bfqq
406	* would be stably merged with itself. To avoid this anomaly,
407	* we cancel the stable merge if
408	* bic->stable_merge_bfqq == bfqq.
409	*/
410	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[actuator_idx];
411
412	/* Clear bic pointer if bfqq is detached from this bic */
413	if (old_bfqq && old_bfqq->bic == bic)
414	old_bfqq->bic = NULL;
415
416	if (is_sync)
417	bic->bfqq[1][actuator_idx] = bfqq;
418	else
419	bic->bfqq[0][actuator_idx] = bfqq;
420
421	if (bfqq && bfqq_data->stable_merge_bfqq == bfqq) {
422	/*
423	* Actually, these same instructions are executed also
424	* in bfq_setup_cooperator, in case of abort or actual
425	* execution of a stable merge. We could avoid
426	* repeating these instructions there too, but if we
427	* did so, we would nest even more complexity in this
428	* function.
429	*/
430	bfq_put_stable_ref(bfqq: bfqq_data->stable_merge_bfqq);
431
432	bfqq_data->stable_merge_bfqq = NULL;
433	}
434	}
435
436	struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic)
437	{
438	return bic->icq.q->elevator->elevator_data;
439	}
440
441	/**
442	* icq_to_bic - convert iocontext queue structure to bfq_io_cq.
443	* @icq: the iocontext queue.
444	*/
445	static struct bfq_io_cq *icq_to_bic(struct io_cq *icq)
446	{
447	/* bic->icq is the first member, %NULL will convert to %NULL */
448	return container_of(icq, struct bfq_io_cq, icq);
449	}
450
451	/**
452	* bfq_bic_lookup - search into @ioc a bic associated to @bfqd.
453	* @q: the request queue.
454	*/
455	static struct bfq_io_cq *bfq_bic_lookup(struct request_queue *q)
456	{
457	struct bfq_io_cq *icq;
458	unsigned long flags;
459
460	if (!current->io_context)
461	return NULL;
462
463	spin_lock_irqsave(&q->queue_lock, flags);
464	icq = icq_to_bic(icq: ioc_lookup_icq(q));
465	spin_unlock_irqrestore(lock: &q->queue_lock, flags);
466
467	return icq;
468	}
469
470	/*
471	* Scheduler run of queue, if there are requests pending and no one in the
472	* driver that will restart queueing.
473	*/
474	void bfq_schedule_dispatch(struct bfq_data *bfqd)
475	{
476	lockdep_assert_held(&bfqd->lock);
477
478	if (bfqd->queued != 0) {
479	bfq_log(bfqd, "schedule dispatch");
480	blk_mq_run_hw_queues(q: bfqd->queue, async: true);
481	}
482	}
483
484	#define bfq_class_idle(bfqq) ((bfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
485
486	#define bfq_sample_valid(samples) ((samples) > 80)
487
488	/*
489	* Lifted from AS - choose which of rq1 and rq2 that is best served now.
490	* We choose the request that is closer to the head right now. Distance
491	* behind the head is penalized and only allowed to a certain extent.
492	*/
493	static struct request *bfq_choose_req(struct bfq_data *bfqd,
494	struct request *rq1,
495	struct request *rq2,
496	sector_t last)
497	{
498	sector_t s1, s2, d1 = 0, d2 = 0;
499	unsigned long back_max;
500	#define BFQ_RQ1_WRAP 0x01 /* request 1 wraps */
501	#define BFQ_RQ2_WRAP 0x02 /* request 2 wraps */
502	unsigned int wrap = 0; /* bit mask: requests behind the disk head? */
503
504	if (!rq1 || rq1 == rq2)
505	return rq2;
506	if (!rq2)
507	return rq1;
508
509	if (rq_is_sync(rq: rq1) && !rq_is_sync(rq: rq2))
510	return rq1;
511	else if (rq_is_sync(rq: rq2) && !rq_is_sync(rq: rq1))
512	return rq2;
513	if ((rq1->cmd_flags & REQ_META) && !(rq2->cmd_flags & REQ_META))
514	return rq1;
515	else if ((rq2->cmd_flags & REQ_META) && !(rq1->cmd_flags & REQ_META))
516	return rq2;
517
518	s1 = blk_rq_pos(rq: rq1);
519	s2 = blk_rq_pos(rq: rq2);
520
521	/*
522	* By definition, 1KiB is 2 sectors.
523	*/
524	back_max = bfqd->bfq_back_max * 2;
525
526	/*
527	* Strict one way elevator _except_ in the case where we allow
528	* short backward seeks which are biased as twice the cost of a
529	* similar forward seek.
530	*/
531	if (s1 >= last)
532	d1 = s1 - last;
533	else if (s1 + back_max >= last)
534	d1 = (last - s1) * bfqd->bfq_back_penalty;
535	else
536	wrap |= BFQ_RQ1_WRAP;
537
538	if (s2 >= last)
539	d2 = s2 - last;
540	else if (s2 + back_max >= last)
541	d2 = (last - s2) * bfqd->bfq_back_penalty;
542	else
543	wrap |= BFQ_RQ2_WRAP;
544
545	/* Found required data */
546
547	/*
548	* By doing switch() on the bit mask "wrap" we avoid having to
549	* check two variables for all permutations: --> faster!
550	*/
551	switch (wrap) {
552	case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
553	if (d1 < d2)
554	return rq1;
555	else if (d2 < d1)
556	return rq2;
557
558	if (s1 >= s2)
559	return rq1;
560	else
561	return rq2;
562
563	case BFQ_RQ2_WRAP:
564	return rq1;
565	case BFQ_RQ1_WRAP:
566	return rq2;
567	case BFQ_RQ1_WRAP|BFQ_RQ2_WRAP: /* both rqs wrapped */
568	default:
569	/*
570	* Since both rqs are wrapped,
571	* start with the one that's further behind head
572	* (--> only *one* back seek required),
573	* since back seek takes more time than forward.
574	*/
575	if (s1 <= s2)
576	return rq1;
577	else
578	return rq2;
579	}
580	}
581
582	#define BFQ_LIMIT_INLINE_DEPTH 16
583
584	#ifdef CONFIG_BFQ_GROUP_IOSCHED
585	static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
586	{
587	struct bfq_data *bfqd = bfqq->bfqd;
588	struct bfq_entity *entity = &bfqq->entity;
589	struct bfq_entity *inline_entities[BFQ_LIMIT_INLINE_DEPTH];
590	struct bfq_entity **entities = inline_entities;
591	int depth, level, alloc_depth = BFQ_LIMIT_INLINE_DEPTH;
592	int class_idx = bfqq->ioprio_class - 1;
593	struct bfq_sched_data *sched_data;
594	unsigned long wsum;
595	bool ret = false;
596
597	if (!entity->on_st_or_in_serv)
598	return false;
599
600	retry:
601	spin_lock_irq(lock: &bfqd->lock);
602	/* +1 for bfqq entity, root cgroup not included */
603	depth = bfqg_to_blkg(bfqg: bfqq_group(bfqq))->blkcg->css.cgroup->level + 1;
604	if (depth > alloc_depth) {
605	spin_unlock_irq(lock: &bfqd->lock);
606	if (entities != inline_entities)
607	kfree(objp: entities);
608	entities = kmalloc_array(n: depth, size: sizeof(*entities), GFP_NOIO);
609	if (!entities)
610	return false;
611	alloc_depth = depth;
612	goto retry;
613	}
614
615	sched_data = entity->sched_data;
616	/* Gather our ancestors as we need to traverse them in reverse order */
617	level = 0;
618	for_each_entity(entity) {
619	/*
620	* If at some level entity is not even active, allow request
621	* queueing so that BFQ knows there's work to do and activate
622	* entities.
623	*/
624	if (!entity->on_st_or_in_serv)
625	goto out;
626	/* Uh, more parents than cgroup subsystem thinks? */
627	if (WARN_ON_ONCE(level >= depth))
628	break;
629	entities[level++] = entity;
630	}
631	WARN_ON_ONCE(level != depth);
632	for (level--; level >= 0; level--) {
633	entity = entities[level];
634	if (level > 0) {
635	wsum = bfq_entity_service_tree(entity)->wsum;
636	} else {
637	int i;
638	/*
639	* For bfqq itself we take into account service trees
640	* of all higher priority classes and multiply their
641	* weights so that low prio queue from higher class
642	* gets more requests than high prio queue from lower
643	* class.
644	*/
645	wsum = 0;
646	for (i = 0; i <= class_idx; i++) {
647	wsum = wsum * IOPRIO_BE_NR +
648	sched_data->service_tree[i].wsum;
649	}
650	}
651	if (!wsum)
652	continue;
653	limit = DIV_ROUND_CLOSEST(limit * entity->weight, wsum);
654	if (entity->allocated >= limit) {
655	bfq_log_bfqq(bfqq->bfqd, bfqq,
656	"too many requests: allocated %d limit %d level %d",
657	entity->allocated, limit, level);
658	ret = true;
659	break;
660	}
661	}
662	out:
663	spin_unlock_irq(lock: &bfqd->lock);
664	if (entities != inline_entities)
665	kfree(objp: entities);
666	return ret;
667	}
668	#else
669	static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
670	{
671	return false;
672	}
673	#endif
674
675	/*
676	* Async I/O can easily starve sync I/O (both sync reads and sync
677	* writes), by consuming all tags. Similarly, storms of sync writes,
678	* such as those that sync(2) may trigger, can starve sync reads.
679	* Limit depths of async I/O and sync writes so as to counter both
680	* problems.
681	*
682	* Also if a bfq queue or its parent cgroup consume more tags than would be
683	* appropriate for their weight, we trim the available tag depth to 1. This
684	* avoids a situation where one cgroup can starve another cgroup from tags and
685	* thus block service differentiation among cgroups. Note that because the
686	* queue / cgroup already has many requests allocated and queued, this does not
687	* significantly affect service guarantees coming from the BFQ scheduling
688	* algorithm.
689	*/
690	static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
691	{
692	struct bfq_data *bfqd = data->q->elevator->elevator_data;
693	struct bfq_io_cq *bic = bfq_bic_lookup(q: data->q);
694	int depth;
695	unsigned limit = data->q->nr_requests;
696	unsigned int act_idx;
697
698	/* Sync reads have full depth available */
699	if (op_is_sync(op: opf) && !op_is_write(op: opf)) {
700	depth = 0;
701	} else {
702	depth = bfqd->word_depths[!!bfqd->wr_busy_queues][op_is_sync(op: opf)];
703	limit = (limit * depth) >> bfqd->full_depth_shift;
704	}
705
706	for (act_idx = 0; bic && act_idx < bfqd->num_actuators; act_idx++) {
707	struct bfq_queue *bfqq =
708	bic_to_bfqq(bic, is_sync: op_is_sync(op: opf), actuator_idx: act_idx);
709
710	/*
711	* Does queue (or any parent entity) exceed number of
712	* requests that should be available to it? Heavily
713	* limit depth so that it cannot consume more
714	* available requests and thus starve other entities.
715	*/
716	if (bfqq && bfqq_request_over_limit(bfqq, limit)) {
717	depth = 1;
718	break;
719	}
720	}
721	bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
722	__func__, bfqd->wr_busy_queues, op_is_sync(opf), depth);
723	if (depth)
724	data->shallow_depth = depth;
725	}
726
727	static struct bfq_queue *
728	bfq_rq_pos_tree_lookup(struct bfq_data *bfqd, struct rb_root *root,
729	sector_t sector, struct rb_node **ret_parent,
730	struct rb_node ***rb_link)
731	{
732	struct rb_node **p, *parent;
733	struct bfq_queue *bfqq = NULL;
734
735	parent = NULL;
736	p = &root->rb_node;
737	while (*p) {
738	struct rb_node **n;
739
740	parent = *p;
741	bfqq = rb_entry(parent, struct bfq_queue, pos_node);
742
743	/*
744	* Sort strictly based on sector. Smallest to the left,
745	* largest to the right.
746	*/
747	if (sector > blk_rq_pos(rq: bfqq->next_rq))
748	n = &(*p)->rb_right;
749	else if (sector < blk_rq_pos(rq: bfqq->next_rq))
750	n = &(*p)->rb_left;
751	else
752	break;
753	p = n;
754	bfqq = NULL;
755	}
756
757	*ret_parent = parent;
758	if (rb_link)
759	*rb_link = p;
760
761	bfq_log(bfqd, "rq_pos_tree_lookup %llu: returning %d",
762	(unsigned long long)sector,
763	bfqq ? bfqq->pid : 0);
764
765	return bfqq;
766	}
767
768	static bool bfq_too_late_for_merging(struct bfq_queue *bfqq)
769	{
770	return bfqq->service_from_backlogged > 0 &&
771	time_is_before_jiffies(bfqq->first_IO_time +
772	bfq_merge_time_limit);
773	}
774
775	/*
776	* The following function is not marked as __cold because it is
777	* actually cold, but for the same performance goal described in the
778	* comments on the likely() at the beginning of
779	* bfq_setup_cooperator(). Unexpectedly, to reach an even lower
780	* execution time for the case where this function is not invoked, we
781	* had to add an unlikely() in each involved if().
782	*/
783	void __cold
784	bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq)
785	{
786	struct rb_node **p, *parent;
787	struct bfq_queue *__bfqq;
788
789	if (bfqq->pos_root) {
790	rb_erase(&bfqq->pos_node, bfqq->pos_root);
791	bfqq->pos_root = NULL;
792	}
793
794	/* oom_bfqq does not participate in queue merging */
795	if (bfqq == &bfqd->oom_bfqq)
796	return;
797
798	/*
799	* bfqq cannot be merged any longer (see comments in
800	* bfq_setup_cooperator): no point in adding bfqq into the
801	* position tree.
802	*/
803	if (bfq_too_late_for_merging(bfqq))
804	return;
805
806	if (bfq_class_idle(bfqq))
807	return;
808	if (!bfqq->next_rq)
809	return;
810
811	bfqq->pos_root = &bfqq_group(bfqq)->rq_pos_tree;
812	__bfqq = bfq_rq_pos_tree_lookup(bfqd, root: bfqq->pos_root,
813	sector: blk_rq_pos(rq: bfqq->next_rq), ret_parent: &parent, rb_link: &p);
814	if (!__bfqq) {
815	rb_link_node(node: &bfqq->pos_node, parent, rb_link: p);
816	rb_insert_color(&bfqq->pos_node, bfqq->pos_root);
817	} else
818	bfqq->pos_root = NULL;
819	}
820
821	/*
822	* The following function returns false either if every active queue
823	* must receive the same share of the throughput (symmetric scenario),
824	* or, as a special case, if bfqq must receive a share of the
825	* throughput lower than or equal to the share that every other active
826	* queue must receive. If bfqq does sync I/O, then these are the only
827	* two cases where bfqq happens to be guaranteed its share of the
828	* throughput even if I/O dispatching is not plugged when bfqq remains
829	* temporarily empty (for more details, see the comments in the
830	* function bfq_better_to_idle()). For this reason, the return value
831	* of this function is used to check whether I/O-dispatch plugging can
832	* be avoided.
833	*
834	* The above first case (symmetric scenario) occurs when:
835	* 1) all active queues have the same weight,
836	* 2) all active queues belong to the same I/O-priority class,
837	* 3) all active groups at the same level in the groups tree have the same
838	* weight,
839	* 4) all active groups at the same level in the groups tree have the same
840	* number of children.
841	*
842	* Unfortunately, keeping the necessary state for evaluating exactly
843	* the last two symmetry sub-conditions above would be quite complex
844	* and time consuming. Therefore this function evaluates, instead,
845	* only the following stronger three sub-conditions, for which it is
846	* much easier to maintain the needed state:
847	* 1) all active queues have the same weight,
848	* 2) all active queues belong to the same I/O-priority class,
849	* 3) there is at most one active group.
850	* In particular, the last condition is always true if hierarchical
851	* support or the cgroups interface are not enabled, thus no state
852	* needs to be maintained in this case.
853	*/
854	static bool bfq_asymmetric_scenario(struct bfq_data *bfqd,
855	struct bfq_queue *bfqq)
856	{
857	bool smallest_weight = bfqq &&
858	bfqq->weight_counter &&
859	bfqq->weight_counter ==
860	container_of(
861	rb_first_cached(&bfqd->queue_weights_tree),
862	struct bfq_weight_counter,
863	weights_node);
864
865	/*
866	* For queue weights to differ, queue_weights_tree must contain
867	* at least two nodes.
868	*/
869	bool varied_queue_weights = !smallest_weight &&
870	!RB_EMPTY_ROOT(&bfqd->queue_weights_tree.rb_root) &&
871	(bfqd->queue_weights_tree.rb_root.rb_node->rb_left ||
872	bfqd->queue_weights_tree.rb_root.rb_node->rb_right);
873
874	bool multiple_classes_busy =
875	(bfqd->busy_queues[0] && bfqd->busy_queues[1]) ||
876	(bfqd->busy_queues[0] && bfqd->busy_queues[2]) ||
877	(bfqd->busy_queues[1] && bfqd->busy_queues[2]);
878
879	return varied_queue_weights || multiple_classes_busy
880	#ifdef CONFIG_BFQ_GROUP_IOSCHED
881	|| bfqd->num_groups_with_pending_reqs > 1
882	#endif
883	;
884	}
885
886	/*
887	* If the weight-counter tree passed as input contains no counter for
888	* the weight of the input queue, then add that counter; otherwise just
889	* increment the existing counter.
890	*
891	* Note that weight-counter trees contain few nodes in mostly symmetric
892	* scenarios. For example, if all queues have the same weight, then the
893	* weight-counter tree for the queues may contain at most one node.
894	* This holds even if low_latency is on, because weight-raised queues
895	* are not inserted in the tree.
896	* In most scenarios, the rate at which nodes are created/destroyed
897	* should be low too.
898	*/
899	void bfq_weights_tree_add(struct bfq_queue *bfqq)
900	{
901	struct rb_root_cached *root = &bfqq->bfqd->queue_weights_tree;
902	struct bfq_entity *entity = &bfqq->entity;
903	struct rb_node **new = &(root->rb_root.rb_node), *parent = NULL;
904	bool leftmost = true;
905
906	/*
907	* Do not insert if the queue is already associated with a
908	* counter, which happens if:
909	* 1) a request arrival has caused the queue to become both
910	* non-weight-raised, and hence change its weight, and
911	* backlogged; in this respect, each of the two events
912	* causes an invocation of this function,
913	* 2) this is the invocation of this function caused by the
914	* second event. This second invocation is actually useless,
915	* and we handle this fact by exiting immediately. More
916	* efficient or clearer solutions might possibly be adopted.
917	*/
918	if (bfqq->weight_counter)
919	return;
920
921	while (*new) {
922	struct bfq_weight_counter *__counter = container_of(*new,
923	struct bfq_weight_counter,
924	weights_node);
925	parent = *new;
926
927	if (entity->weight == __counter->weight) {
928	bfqq->weight_counter = __counter;
929	goto inc_counter;
930	}
931	if (entity->weight < __counter->weight)
932	new = &((*new)->rb_left);
933	else {
934	new = &((*new)->rb_right);
935	leftmost = false;
936	}
937	}
938
939	bfqq->weight_counter = kzalloc(size: sizeof(struct bfq_weight_counter),
940	GFP_ATOMIC);
941
942	/*
943	* In the unlucky event of an allocation failure, we just
944	* exit. This will cause the weight of queue to not be
945	* considered in bfq_asymmetric_scenario, which, in its turn,
946	* causes the scenario to be deemed wrongly symmetric in case
947	* bfqq's weight would have been the only weight making the
948	* scenario asymmetric. On the bright side, no unbalance will
949	* however occur when bfqq becomes inactive again (the
950	* invocation of this function is triggered by an activation
951	* of queue). In fact, bfq_weights_tree_remove does nothing
952	* if !bfqq->weight_counter.
953	*/
954	if (unlikely(!bfqq->weight_counter))
955	return;
956
957	bfqq->weight_counter->weight = entity->weight;
958	rb_link_node(node: &bfqq->weight_counter->weights_node, parent, rb_link: new);
959	rb_insert_color_cached(node: &bfqq->weight_counter->weights_node, root,
960	leftmost);
961
962	inc_counter:
963	bfqq->weight_counter->num_active++;
964	bfqq->ref++;
965	}
966
967	/*
968	* Decrement the weight counter associated with the queue, and, if the
969	* counter reaches 0, remove the counter from the tree.
970	* See the comments to the function bfq_weights_tree_add() for considerations
971	* about overhead.
972	*/
973	void bfq_weights_tree_remove(struct bfq_queue *bfqq)
974	{
975	struct rb_root_cached *root;
976
977	if (!bfqq->weight_counter)
978	return;
979
980	root = &bfqq->bfqd->queue_weights_tree;
981	bfqq->weight_counter->num_active--;
982	if (bfqq->weight_counter->num_active > 0)
983	goto reset_entity_pointer;
984
985	rb_erase_cached(node: &bfqq->weight_counter->weights_node, root);
986	kfree(objp: bfqq->weight_counter);
987
988	reset_entity_pointer:
989	bfqq->weight_counter = NULL;
990	bfq_put_queue(bfqq);
991	}
992
993	/*
994	* Return expired entry, or NULL to just start from scratch in rbtree.
995	*/
996	static struct request *bfq_check_fifo(struct bfq_queue *bfqq,
997	struct request *last)
998	{
999	struct request *rq;
1000
1001	if (bfq_bfqq_fifo_expire(bfqq))
1002	return NULL;
1003
1004	bfq_mark_bfqq_fifo_expire(bfqq);
1005
1006	rq = rq_entry_fifo(bfqq->fifo.next);
1007
1008	if (rq == last || blk_time_get_ns() < rq->fifo_time)
1009	return NULL;
1010
1011	bfq_log_bfqq(bfqq->bfqd, bfqq, "check_fifo: returned %p", rq);
1012	return rq;
1013	}
1014
1015	static struct request *bfq_find_next_rq(struct bfq_data *bfqd,
1016	struct bfq_queue *bfqq,
1017	struct request *last)
1018	{
1019	struct rb_node *rbnext = rb_next(&last->rb_node);
1020	struct rb_node *rbprev = rb_prev(&last->rb_node);
1021	struct request *next, *prev = NULL;
1022
1023	/* Follow expired path, else get first next available. */
1024	next = bfq_check_fifo(bfqq, last);
1025	if (next)
1026	return next;
1027
1028	if (rbprev)
1029	prev = rb_entry_rq(rbprev);
1030
1031	if (rbnext)
1032	next = rb_entry_rq(rbnext);
1033	else {
1034	rbnext = rb_first(&bfqq->sort_list);
1035	if (rbnext && rbnext != &last->rb_node)
1036	next = rb_entry_rq(rbnext);
1037	}
1038
1039	return bfq_choose_req(bfqd, rq1: next, rq2: prev, last: blk_rq_pos(rq: last));
1040	}
1041
1042	/* see the definition of bfq_async_charge_factor for details */
1043	static unsigned long bfq_serv_to_charge(struct request *rq,
1044	struct bfq_queue *bfqq)
1045	{
1046	if (bfq_bfqq_sync(bfqq) || bfqq->wr_coeff > 1 ||
1047	bfq_asymmetric_scenario(bfqd: bfqq->bfqd, bfqq))
1048	return blk_rq_sectors(rq);
1049
1050	return blk_rq_sectors(rq) * bfq_async_charge_factor;
1051	}
1052
1053	/**
1054	* bfq_updated_next_req - update the queue after a new next_rq selection.
1055	* @bfqd: the device data the queue belongs to.
1056	* @bfqq: the queue to update.
1057	*
1058	* If the first request of a queue changes we make sure that the queue
1059	* has enough budget to serve at least its first request (if the
1060	* request has grown). We do this because if the queue has not enough
1061	* budget for its first request, it has to go through two dispatch
1062	* rounds to actually get it dispatched.
1063	*/
1064	static void bfq_updated_next_req(struct bfq_data *bfqd,
1065	struct bfq_queue *bfqq)
1066	{
1067	struct bfq_entity *entity = &bfqq->entity;
1068	struct request *next_rq = bfqq->next_rq;
1069	unsigned long new_budget;
1070
1071	if (!next_rq)
1072	return;
1073
1074	if (bfqq == bfqd->in_service_queue)
1075	/*
1076	* In order not to break guarantees, budgets cannot be
1077	* changed after an entity has been selected.
1078	*/
1079	return;
1080
1081	new_budget = max_t(unsigned long,
1082	max_t(unsigned long, bfqq->max_budget,
1083	bfq_serv_to_charge(next_rq, bfqq)),
1084	entity->service);
1085	if (entity->budget != new_budget) {
1086	entity->budget = new_budget;
1087	bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",
1088	new_budget);
1089	bfq_requeue_bfqq(bfqd, bfqq, expiration: false);
1090	}
1091	}
1092
1093	static unsigned int bfq_wr_duration(struct bfq_data *bfqd)
1094	{
1095	u64 dur;
1096
1097	dur = bfqd->rate_dur_prod;
1098	do_div(dur, bfqd->peak_rate);
1099
1100	/*
1101	* Limit duration between 3 and 25 seconds. The upper limit
1102	* has been conservatively set after the following worst case:
1103	* on a QEMU/KVM virtual machine
1104	* - running in a slow PC
1105	* - with a virtual disk stacked on a slow low-end 5400rpm HDD
1106	* - serving a heavy I/O workload, such as the sequential reading
1107	* of several files
1108	* mplayer took 23 seconds to start, if constantly weight-raised.
1109	*
1110	* As for higher values than that accommodating the above bad
1111	* scenario, tests show that higher values would often yield
1112	* the opposite of the desired result, i.e., would worsen
1113	* responsiveness by allowing non-interactive applications to
1114	* preserve weight raising for too long.
1115	*
1116	* On the other end, lower values than 3 seconds make it
1117	* difficult for most interactive tasks to complete their jobs
1118	* before weight-raising finishes.
1119	*/
1120	return clamp_val(dur, msecs_to_jiffies(3000), msecs_to_jiffies(25000));
1121	}
1122
1123	/* switch back from soft real-time to interactive weight raising */
1124	static void switch_back_to_interactive_wr(struct bfq_queue *bfqq,
1125	struct bfq_data *bfqd)
1126	{
1127	bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1128	bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1129	bfqq->last_wr_start_finish = bfqq->wr_start_at_switch_to_srt;
1130	}
1131
1132	static void
1133	bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
1134	struct bfq_io_cq *bic, bool bfq_already_existing)
1135	{
1136	unsigned int old_wr_coeff = 1;
1137	bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
1138	unsigned int a_idx = bfqq->actuator_idx;
1139	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
1140
1141	if (bfqq_data->saved_has_short_ttime)
1142	bfq_mark_bfqq_has_short_ttime(bfqq);
1143	else
1144	bfq_clear_bfqq_has_short_ttime(bfqq);
1145
1146	if (bfqq_data->saved_IO_bound)
1147	bfq_mark_bfqq_IO_bound(bfqq);
1148	else
1149	bfq_clear_bfqq_IO_bound(bfqq);
1150
1151	bfqq->last_serv_time_ns = bfqq_data->saved_last_serv_time_ns;
1152	bfqq->inject_limit = bfqq_data->saved_inject_limit;
1153	bfqq->decrease_time_jif = bfqq_data->saved_decrease_time_jif;
1154
1155	bfqq->entity.new_weight = bfqq_data->saved_weight;
1156	bfqq->ttime = bfqq_data->saved_ttime;
1157	bfqq->io_start_time = bfqq_data->saved_io_start_time;
1158	bfqq->tot_idle_time = bfqq_data->saved_tot_idle_time;
1159	/*
1160	* Restore weight coefficient only if low_latency is on
1161	*/
1162	if (bfqd->low_latency) {
1163	old_wr_coeff = bfqq->wr_coeff;
1164	bfqq->wr_coeff = bfqq_data->saved_wr_coeff;
1165	}
1166	bfqq->service_from_wr = bfqq_data->saved_service_from_wr;
1167	bfqq->wr_start_at_switch_to_srt =
1168	bfqq_data->saved_wr_start_at_switch_to_srt;
1169	bfqq->last_wr_start_finish = bfqq_data->saved_last_wr_start_finish;
1170	bfqq->wr_cur_max_time = bfqq_data->saved_wr_cur_max_time;
1171
1172	if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
1173	time_is_before_jiffies(bfqq->last_wr_start_finish +
1174	bfqq->wr_cur_max_time))) {
1175	if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
1176	!bfq_bfqq_in_large_burst(bfqq) &&
1177	time_is_after_eq_jiffies(bfqq->wr_start_at_switch_to_srt +
1178	bfq_wr_duration(bfqd))) {
1179	switch_back_to_interactive_wr(bfqq, bfqd);
1180	} else {
1181	bfqq->wr_coeff = 1;
1182	bfq_log_bfqq(bfqq->bfqd, bfqq,
1183	"resume state: switching off wr");
1184	}
1185	}
1186
1187	/* make sure weight will be updated, however we got here */
1188	bfqq->entity.prio_changed = 1;
1189
1190	if (likely(!busy))
1191	return;
1192
1193	if (old_wr_coeff == 1 && bfqq->wr_coeff > 1)
1194	bfqd->wr_busy_queues++;
1195	else if (old_wr_coeff > 1 && bfqq->wr_coeff == 1)
1196	bfqd->wr_busy_queues--;
1197	}
1198
1199	static int bfqq_process_refs(struct bfq_queue *bfqq)
1200	{
1201	return bfqq->ref - bfqq->entity.allocated -
1202	bfqq->entity.on_st_or_in_serv -
1203	(bfqq->weight_counter != NULL) - bfqq->stable_ref;
1204	}
1205
1206	/* Empty burst list and add just bfqq (see comments on bfq_handle_burst) */
1207	static void bfq_reset_burst_list(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1208	{
1209	struct bfq_queue *item;
1210	struct hlist_node *n;
1211
1212	hlist_for_each_entry_safe(item, n, &bfqd->burst_list, burst_list_node)
1213	hlist_del_init(n: &item->burst_list_node);
1214
1215	/*
1216	* Start the creation of a new burst list only if there is no
1217	* active queue. See comments on the conditional invocation of
1218	* bfq_handle_burst().
1219	*/
1220	if (bfq_tot_busy_queues(bfqd) == 0) {
1221	hlist_add_head(n: &bfqq->burst_list_node, h: &bfqd->burst_list);
1222	bfqd->burst_size = 1;
1223	} else
1224	bfqd->burst_size = 0;
1225
1226	bfqd->burst_parent_entity = bfqq->entity.parent;
1227	}
1228
1229	/* Add bfqq to the list of queues in current burst (see bfq_handle_burst) */
1230	static void bfq_add_to_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1231	{
1232	/* Increment burst size to take into account also bfqq */
1233	bfqd->burst_size++;
1234
1235	if (bfqd->burst_size == bfqd->bfq_large_burst_thresh) {
1236	struct bfq_queue *pos, *bfqq_item;
1237	struct hlist_node *n;
1238
1239	/*
1240	* Enough queues have been activated shortly after each
1241	* other to consider this burst as large.
1242	*/
1243	bfqd->large_burst = true;
1244
1245	/*
1246	* We can now mark all queues in the burst list as
1247	* belonging to a large burst.
1248	*/
1249	hlist_for_each_entry(bfqq_item, &bfqd->burst_list,
1250	burst_list_node)
1251	bfq_mark_bfqq_in_large_burst(bfqq: bfqq_item);
1252	bfq_mark_bfqq_in_large_burst(bfqq);
1253
1254	/*
1255	* From now on, and until the current burst finishes, any
1256	* new queue being activated shortly after the last queue
1257	* was inserted in the burst can be immediately marked as
1258	* belonging to a large burst. So the burst list is not
1259	* needed any more. Remove it.
1260	*/
1261	hlist_for_each_entry_safe(pos, n, &bfqd->burst_list,
1262	burst_list_node)
1263	hlist_del_init(n: &pos->burst_list_node);
1264	} else /*
1265	* Burst not yet large: add bfqq to the burst list. Do
1266	* not increment the ref counter for bfqq, because bfqq
1267	* is removed from the burst list before freeing bfqq
1268	* in put_queue.
1269	*/
1270	hlist_add_head(n: &bfqq->burst_list_node, h: &bfqd->burst_list);
1271	}
1272
1273	/*
1274	* If many queues belonging to the same group happen to be created
1275	* shortly after each other, then the processes associated with these
1276	* queues have typically a common goal. In particular, bursts of queue
1277	* creations are usually caused by services or applications that spawn
1278	* many parallel threads/processes. Examples are systemd during boot,
1279	* or git grep. To help these processes get their job done as soon as
1280	* possible, it is usually better to not grant either weight-raising
1281	* or device idling to their queues, unless these queues must be
1282	* protected from the I/O flowing through other active queues.
1283	*
1284	* In this comment we describe, firstly, the reasons why this fact
1285	* holds, and, secondly, the next function, which implements the main
1286	* steps needed to properly mark these queues so that they can then be
1287	* treated in a different way.
1288	*
1289	* The above services or applications benefit mostly from a high
1290	* throughput: the quicker the requests of the activated queues are
1291	* cumulatively served, the sooner the target job of these queues gets
1292	* completed. As a consequence, weight-raising any of these queues,
1293	* which also implies idling the device for it, is almost always
1294	* counterproductive, unless there are other active queues to isolate
1295	* these new queues from. If there no other active queues, then
1296	* weight-raising these new queues just lowers throughput in most
1297	* cases.
1298	*
1299	* On the other hand, a burst of queue creations may be caused also by
1300	* the start of an application that does not consist of a lot of
1301	* parallel I/O-bound threads. In fact, with a complex application,
1302	* several short processes may need to be executed to start-up the
1303	* application. In this respect, to start an application as quickly as
1304	* possible, the best thing to do is in any case to privilege the I/O
1305	* related to the application with respect to all other
1306	* I/O. Therefore, the best strategy to start as quickly as possible
1307	* an application that causes a burst of queue creations is to
1308	* weight-raise all the queues created during the burst. This is the
1309	* exact opposite of the best strategy for the other type of bursts.
1310	*
1311	* In the end, to take the best action for each of the two cases, the
1312	* two types of bursts need to be distinguished. Fortunately, this
1313	* seems relatively easy, by looking at the sizes of the bursts. In
1314	* particular, we found a threshold such that only bursts with a
1315	* larger size than that threshold are apparently caused by
1316	* services or commands such as systemd or git grep. For brevity,
1317	* hereafter we call just 'large' these bursts. BFQ *does not*
1318	* weight-raise queues whose creation occurs in a large burst. In
1319	* addition, for each of these queues BFQ performs or does not perform
1320	* idling depending on which choice boosts the throughput more. The
1321	* exact choice depends on the device and request pattern at
1322	* hand.
1323	*
1324	* Unfortunately, false positives may occur while an interactive task
1325	* is starting (e.g., an application is being started). The
1326	* consequence is that the queues associated with the task do not
1327	* enjoy weight raising as expected. Fortunately these false positives
1328	* are very rare. They typically occur if some service happens to
1329	* start doing I/O exactly when the interactive task starts.
1330	*
1331	* Turning back to the next function, it is invoked only if there are
1332	* no active queues (apart from active queues that would belong to the
1333	* same, possible burst bfqq would belong to), and it implements all
1334	* the steps needed to detect the occurrence of a large burst and to
1335	* properly mark all the queues belonging to it (so that they can then
1336	* be treated in a different way). This goal is achieved by
1337	* maintaining a "burst list" that holds, temporarily, the queues that
1338	* belong to the burst in progress. The list is then used to mark
1339	* these queues as belonging to a large burst if the burst does become
1340	* large. The main steps are the following.
1341	*
1342	* . when the very first queue is created, the queue is inserted into the
1343	* list (as it could be the first queue in a possible burst)
1344	*
1345	* . if the current burst has not yet become large, and a queue Q that does
1346	* not yet belong to the burst is activated shortly after the last time
1347	* at which a new queue entered the burst list, then the function appends
1348	* Q to the burst list
1349	*
1350	* . if, as a consequence of the previous step, the burst size reaches
1351	* the large-burst threshold, then
1352	*
1353	* . all the queues in the burst list are marked as belonging to a
1354	* large burst
1355	*
1356	* . the burst list is deleted; in fact, the burst list already served
1357	* its purpose (keeping temporarily track of the queues in a burst,
1358	* so as to be able to mark them as belonging to a large burst in the
1359	* previous sub-step), and now is not needed any more
1360	*
1361	* . the device enters a large-burst mode
1362	*
1363	* . if a queue Q that does not belong to the burst is created while
1364	* the device is in large-burst mode and shortly after the last time
1365	* at which a queue either entered the burst list or was marked as
1366	* belonging to the current large burst, then Q is immediately marked
1367	* as belonging to a large burst.
1368	*
1369	* . if a queue Q that does not belong to the burst is created a while
1370	* later, i.e., not shortly after, than the last time at which a queue
1371	* either entered the burst list or was marked as belonging to the
1372	* current large burst, then the current burst is deemed as finished and:
1373	*
1374	* . the large-burst mode is reset if set
1375	*
1376	* . the burst list is emptied
1377	*
1378	* . Q is inserted in the burst list, as Q may be the first queue
1379	* in a possible new burst (then the burst list contains just Q
1380	* after this step).
1381	*/
1382	static void bfq_handle_burst(struct bfq_data *bfqd, struct bfq_queue *bfqq)
1383	{
1384	/*
1385	* If bfqq is already in the burst list or is part of a large
1386	* burst, or finally has just been split, then there is
1387	* nothing else to do.
1388	*/
1389	if (!hlist_unhashed(h: &bfqq->burst_list_node) ||
1390	bfq_bfqq_in_large_burst(bfqq) ||
1391	time_is_after_eq_jiffies(bfqq->split_time +
1392	msecs_to_jiffies(10)))
1393	return;
1394
1395	/*
1396	* If bfqq's creation happens late enough, or bfqq belongs to
1397	* a different group than the burst group, then the current
1398	* burst is finished, and related data structures must be
1399	* reset.
1400	*
1401	* In this respect, consider the special case where bfqq is
1402	* the very first queue created after BFQ is selected for this
1403	* device. In this case, last_ins_in_burst and
1404	* burst_parent_entity are not yet significant when we get
1405	* here. But it is easy to verify that, whether or not the
1406	* following condition is true, bfqq will end up being
1407	* inserted into the burst list. In particular the list will
1408	* happen to contain only bfqq. And this is exactly what has
1409	* to happen, as bfqq may be the first queue of the first
1410	* burst.
1411	*/
1412	if (time_is_before_jiffies(bfqd->last_ins_in_burst +
1413	bfqd->bfq_burst_interval) ||
1414	bfqq->entity.parent != bfqd->burst_parent_entity) {
1415	bfqd->large_burst = false;
1416	bfq_reset_burst_list(bfqd, bfqq);
1417	goto end;
1418	}
1419
1420	/*
1421	* If we get here, then bfqq is being activated shortly after the
1422	* last queue. So, if the current burst is also large, we can mark
1423	* bfqq as belonging to this large burst immediately.
1424	*/
1425	if (bfqd->large_burst) {
1426	bfq_mark_bfqq_in_large_burst(bfqq);
1427	goto end;
1428	}
1429
1430	/*
1431	* If we get here, then a large-burst state has not yet been
1432	* reached, but bfqq is being activated shortly after the last
1433	* queue. Then we add bfqq to the burst.
1434	*/
1435	bfq_add_to_burst(bfqd, bfqq);
1436	end:
1437	/*
1438	* At this point, bfqq either has been added to the current
1439	* burst or has caused the current burst to terminate and a
1440	* possible new burst to start. In particular, in the second
1441	* case, bfqq has become the first queue in the possible new
1442	* burst. In both cases last_ins_in_burst needs to be moved
1443	* forward.
1444	*/
1445	bfqd->last_ins_in_burst = jiffies;
1446	}
1447
1448	static int bfq_bfqq_budget_left(struct bfq_queue *bfqq)
1449	{
1450	struct bfq_entity *entity = &bfqq->entity;
1451
1452	return entity->budget - entity->service;
1453	}
1454
1455	/*
1456	* If enough samples have been computed, return the current max budget
1457	* stored in bfqd, which is dynamically updated according to the
1458	* estimated disk peak rate; otherwise return the default max budget
1459	*/
1460	static int bfq_max_budget(struct bfq_data *bfqd)
1461	{
1462	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1463	return bfq_default_max_budget;
1464	else
1465	return bfqd->bfq_max_budget;
1466	}
1467
1468	/*
1469	* Return min budget, which is a fraction of the current or default
1470	* max budget (trying with 1/32)
1471	*/
1472	static int bfq_min_budget(struct bfq_data *bfqd)
1473	{
1474	if (bfqd->budgets_assigned < bfq_stats_min_budgets)
1475	return bfq_default_max_budget / 32;
1476	else
1477	return bfqd->bfq_max_budget / 32;
1478	}
1479
1480	/*
1481	* The next function, invoked after the input queue bfqq switches from
1482	* idle to busy, updates the budget of bfqq. The function also tells
1483	* whether the in-service queue should be expired, by returning
1484	* true. The purpose of expiring the in-service queue is to give bfqq
1485	* the chance to possibly preempt the in-service queue, and the reason
1486	* for preempting the in-service queue is to achieve one of the two
1487	* goals below.
1488	*
1489	* 1. Guarantee to bfqq its reserved bandwidth even if bfqq has
1490	* expired because it has remained idle. In particular, bfqq may have
1491	* expired for one of the following two reasons:
1492	*
1493	* - BFQQE_NO_MORE_REQUESTS bfqq did not enjoy any device idling
1494	* and did not make it to issue a new request before its last
1495	* request was served;
1496	*
1497	* - BFQQE_TOO_IDLE bfqq did enjoy device idling, but did not issue
1498	* a new request before the expiration of the idling-time.
1499	*
1500	* Even if bfqq has expired for one of the above reasons, the process
1501	* associated with the queue may be however issuing requests greedily,
1502	* and thus be sensitive to the bandwidth it receives (bfqq may have
1503	* remained idle for other reasons: CPU high load, bfqq not enjoying
1504	* idling, I/O throttling somewhere in the path from the process to
1505	* the I/O scheduler, ...). But if, after every expiration for one of
1506	* the above two reasons, bfqq has to wait for the service of at least
1507	* one full budget of another queue before being served again, then
1508	* bfqq is likely to get a much lower bandwidth or resource time than
1509	* its reserved ones. To address this issue, two countermeasures need
1510	* to be taken.
1511	*
1512	* First, the budget and the timestamps of bfqq need to be updated in
1513	* a special way on bfqq reactivation: they need to be updated as if
1514	* bfqq did not remain idle and did not expire. In fact, if they are
1515	* computed as if bfqq expired and remained idle until reactivation,
1516	* then the process associated with bfqq is treated as if, instead of
1517	* being greedy, it stopped issuing requests when bfqq remained idle,
1518	* and restarts issuing requests only on this reactivation. In other
1519	* words, the scheduler does not help the process recover the "service
1520	* hole" between bfqq expiration and reactivation. As a consequence,
1521	* the process receives a lower bandwidth than its reserved one. In
1522	* contrast, to recover this hole, the budget must be updated as if
1523	* bfqq was not expired at all before this reactivation, i.e., it must
1524	* be set to the value of the remaining budget when bfqq was
1525	* expired. Along the same line, timestamps need to be assigned the
1526	* value they had the last time bfqq was selected for service, i.e.,
1527	* before last expiration. Thus timestamps need to be back-shifted
1528	* with respect to their normal computation (see [1] for more details
1529	* on this tricky aspect).
1530	*
1531	* Secondly, to allow the process to recover the hole, the in-service
1532	* queue must be expired too, to give bfqq the chance to preempt it
1533	* immediately. In fact, if bfqq has to wait for a full budget of the
1534	* in-service queue to be completed, then it may become impossible to
1535	* let the process recover the hole, even if the back-shifted
1536	* timestamps of bfqq are lower than those of the in-service queue. If
1537	* this happens for most or all of the holes, then the process may not
1538	* receive its reserved bandwidth. In this respect, it is worth noting
1539	* that, being the service of outstanding requests unpreemptible, a
1540	* little fraction of the holes may however be unrecoverable, thereby
1541	* causing a little loss of bandwidth.
1542	*
1543	* The last important point is detecting whether bfqq does need this
1544	* bandwidth recovery. In this respect, the next function deems the
1545	* process associated with bfqq greedy, and thus allows it to recover
1546	* the hole, if: 1) the process is waiting for the arrival of a new
1547	* request (which implies that bfqq expired for one of the above two
1548	* reasons), and 2) such a request has arrived soon. The first
1549	* condition is controlled through the flag non_blocking_wait_rq,
1550	* while the second through the flag arrived_in_time. If both
1551	* conditions hold, then the function computes the budget in the
1552	* above-described special way, and signals that the in-service queue
1553	* should be expired. Timestamp back-shifting is done later in
1554	* __bfq_activate_entity.
1555	*
1556	* 2. Reduce latency. Even if timestamps are not backshifted to let
1557	* the process associated with bfqq recover a service hole, bfqq may
1558	* however happen to have, after being (re)activated, a lower finish
1559	* timestamp than the in-service queue. That is, the next budget of
1560	* bfqq may have to be completed before the one of the in-service
1561	* queue. If this is the case, then preempting the in-service queue
1562	* allows this goal to be achieved, apart from the unpreemptible,
1563	* outstanding requests mentioned above.
1564	*
1565	* Unfortunately, regardless of which of the above two goals one wants
1566	* to achieve, service trees need first to be updated to know whether
1567	* the in-service queue must be preempted. To have service trees
1568	* correctly updated, the in-service queue must be expired and
1569	* rescheduled, and bfqq must be scheduled too. This is one of the
1570	* most costly operations (in future versions, the scheduling
1571	* mechanism may be re-designed in such a way to make it possible to
1572	* know whether preemption is needed without needing to update service
1573	* trees). In addition, queue preemptions almost always cause random
1574	* I/O, which may in turn cause loss of throughput. Finally, there may
1575	* even be no in-service queue when the next function is invoked (so,
1576	* no queue to compare timestamps with). Because of these facts, the
1577	* next function adopts the following simple scheme to avoid costly
1578	* operations, too frequent preemptions and too many dependencies on
1579	* the state of the scheduler: it requests the expiration of the
1580	* in-service queue (unconditionally) only for queues that need to
1581	* recover a hole. Then it delegates to other parts of the code the
1582	* responsibility of handling the above case 2.
1583	*/
1584	static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
1585	struct bfq_queue *bfqq,
1586	bool arrived_in_time)
1587	{
1588	struct bfq_entity *entity = &bfqq->entity;
1589
1590	/*
1591	* In the next compound condition, we check also whether there
1592	* is some budget left, because otherwise there is no point in
1593	* trying to go on serving bfqq with this same budget: bfqq
1594	* would be expired immediately after being selected for
1595	* service. This would only cause useless overhead.
1596	*/
1597	if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
1598	bfq_bfqq_budget_left(bfqq) > 0) {
1599	/*
1600	* We do not clear the flag non_blocking_wait_rq here, as
1601	* the latter is used in bfq_activate_bfqq to signal
1602	* that timestamps need to be back-shifted (and is
1603	* cleared right after).
1604	*/
1605
1606	/*
1607	* In next assignment we rely on that either
1608	* entity->service or entity->budget are not updated
1609	* on expiration if bfqq is empty (see
1610	* __bfq_bfqq_recalc_budget). Thus both quantities
1611	* remain unchanged after such an expiration, and the
1612	* following statement therefore assigns to
1613	* entity->budget the remaining budget on such an
1614	* expiration.
1615	*/
1616	entity->budget = min_t(unsigned long,
1617	bfq_bfqq_budget_left(bfqq),
1618	bfqq->max_budget);
1619
1620	/*
1621	* At this point, we have used entity->service to get
1622	* the budget left (needed for updating
1623	* entity->budget). Thus we finally can, and have to,
1624	* reset entity->service. The latter must be reset
1625	* because bfqq would otherwise be charged again for
1626	* the service it has received during its previous
1627	* service slot(s).
1628	*/
1629	entity->service = 0;
1630
1631	return true;
1632	}
1633
1634	/*
1635	* We can finally complete expiration, by setting service to 0.
1636	*/
1637	entity->service = 0;
1638	entity->budget = max_t(unsigned long, bfqq->max_budget,
1639	bfq_serv_to_charge(bfqq->next_rq, bfqq));
1640	bfq_clear_bfqq_non_blocking_wait_rq(bfqq);
1641	return false;
1642	}
1643
1644	/*
1645	* Return the farthest past time instant according to jiffies
1646	* macros.
1647	*/
1648	static unsigned long bfq_smallest_from_now(void)
1649	{
1650	return jiffies - MAX_JIFFY_OFFSET;
1651	}
1652
1653	static void bfq_update_bfqq_wr_on_rq_arrival(struct bfq_data *bfqd,
1654	struct bfq_queue *bfqq,
1655	unsigned int old_wr_coeff,
1656	bool wr_or_deserves_wr,
1657	bool interactive,
1658	bool in_burst,
1659	bool soft_rt)
1660	{
1661	if (old_wr_coeff == 1 && wr_or_deserves_wr) {
1662	/* start a weight-raising period */
1663	if (interactive) {
1664	bfqq->service_from_wr = 0;
1665	bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1666	bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1667	} else {
1668	/*
1669	* No interactive weight raising in progress
1670	* here: assign minus infinity to
1671	* wr_start_at_switch_to_srt, to make sure
1672	* that, at the end of the soft-real-time
1673	* weight raising periods that is starting
1674	* now, no interactive weight-raising period
1675	* may be wrongly considered as still in
1676	* progress (and thus actually started by
1677	* mistake).
1678	*/
1679	bfqq->wr_start_at_switch_to_srt =
1680	bfq_smallest_from_now();
1681	bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1682	BFQ_SOFTRT_WEIGHT_FACTOR;
1683	bfqq->wr_cur_max_time =
1684	bfqd->bfq_wr_rt_max_time;
1685	}
1686
1687	/*
1688	* If needed, further reduce budget to make sure it is
1689	* close to bfqq's backlog, so as to reduce the
1690	* scheduling-error component due to a too large
1691	* budget. Do not care about throughput consequences,
1692	* but only about latency. Finally, do not assign a
1693	* too small budget either, to avoid increasing
1694	* latency by causing too frequent expirations.
1695	*/
1696	bfqq->entity.budget = min_t(unsigned long,
1697	bfqq->entity.budget,
1698	2 * bfq_min_budget(bfqd));
1699	} else if (old_wr_coeff > 1) {
1700	if (interactive) { /* update wr coeff and duration */
1701	bfqq->wr_coeff = bfqd->bfq_wr_coeff;
1702	bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
1703	} else if (in_burst)
1704	bfqq->wr_coeff = 1;
1705	else if (soft_rt) {
1706	/*
1707	* The application is now or still meeting the
1708	* requirements for being deemed soft rt. We
1709	* can then correctly and safely (re)charge
1710	* the weight-raising duration for the
1711	* application with the weight-raising
1712	* duration for soft rt applications.
1713	*
1714	* In particular, doing this recharge now, i.e.,
1715	* before the weight-raising period for the
1716	* application finishes, reduces the probability
1717	* of the following negative scenario:
1718	* 1) the weight of a soft rt application is
1719	* raised at startup (as for any newly
1720	* created application),
1721	* 2) since the application is not interactive,
1722	* at a certain time weight-raising is
1723	* stopped for the application,
1724	* 3) at that time the application happens to
1725	* still have pending requests, and hence
1726	* is destined to not have a chance to be
1727	* deemed soft rt before these requests are
1728	* completed (see the comments to the
1729	* function bfq_bfqq_softrt_next_start()
1730	* for details on soft rt detection),
1731	* 4) these pending requests experience a high
1732	* latency because the application is not
1733	* weight-raised while they are pending.
1734	*/
1735	if (bfqq->wr_cur_max_time !=
1736	bfqd->bfq_wr_rt_max_time) {
1737	bfqq->wr_start_at_switch_to_srt =
1738	bfqq->last_wr_start_finish;
1739
1740	bfqq->wr_cur_max_time =
1741	bfqd->bfq_wr_rt_max_time;
1742	bfqq->wr_coeff = bfqd->bfq_wr_coeff *
1743	BFQ_SOFTRT_WEIGHT_FACTOR;
1744	}
1745	bfqq->last_wr_start_finish = jiffies;
1746	}
1747	}
1748	}
1749
1750	static bool bfq_bfqq_idle_for_long_time(struct bfq_data *bfqd,
1751	struct bfq_queue *bfqq)
1752	{
1753	return bfqq->dispatched == 0 &&
1754	time_is_before_jiffies(
1755	bfqq->budget_timeout +
1756	bfqd->bfq_wr_min_idle_time);
1757	}
1758
1759
1760	/*
1761	* Return true if bfqq is in a higher priority class, or has a higher
1762	* weight than the in-service queue.
1763	*/
1764	static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
1765	struct bfq_queue *in_serv_bfqq)
1766	{
1767	int bfqq_weight, in_serv_weight;
1768
1769	if (bfqq->ioprio_class < in_serv_bfqq->ioprio_class)
1770	return true;
1771
1772	if (in_serv_bfqq->entity.parent == bfqq->entity.parent) {
1773	bfqq_weight = bfqq->entity.weight;
1774	in_serv_weight = in_serv_bfqq->entity.weight;
1775	} else {
1776	if (bfqq->entity.parent)
1777	bfqq_weight = bfqq->entity.parent->weight;
1778	else
1779	bfqq_weight = bfqq->entity.weight;
1780	if (in_serv_bfqq->entity.parent)
1781	in_serv_weight = in_serv_bfqq->entity.parent->weight;
1782	else
1783	in_serv_weight = in_serv_bfqq->entity.weight;
1784	}
1785
1786	return bfqq_weight > in_serv_weight;
1787	}
1788
1789	/*
1790	* Get the index of the actuator that will serve bio.
1791	*/
1792	static unsigned int bfq_actuator_index(struct bfq_data *bfqd, struct bio *bio)
1793	{
1794	unsigned int i;
1795	sector_t end;
1796
1797	/* no search needed if one or zero ranges present */
1798	if (bfqd->num_actuators == 1)
1799	return 0;
1800
1801	/* bio_end_sector(bio) gives the sector after the last one */
1802	end = bio_end_sector(bio) - 1;
1803
1804	for (i = 0; i < bfqd->num_actuators; i++) {
1805	if (end >= bfqd->sector[i] &&
1806	end < bfqd->sector[i] + bfqd->nr_sectors[i])
1807	return i;
1808	}
1809
1810	WARN_ONCE(true,
1811	"bfq_actuator_index: bio sector out of ranges: end=%llu\n",
1812	end);
1813	return 0;
1814	}
1815
1816	static bool bfq_better_to_idle(struct bfq_queue *bfqq);
1817
1818	static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
1819	struct bfq_queue *bfqq,
1820	int old_wr_coeff,
1821	struct request *rq,
1822	bool *interactive)
1823	{
1824	bool soft_rt, in_burst, wr_or_deserves_wr,
1825	bfqq_wants_to_preempt,
1826	idle_for_long_time = bfq_bfqq_idle_for_long_time(bfqd, bfqq),
1827	/*
1828	* See the comments on
1829	* bfq_bfqq_update_budg_for_activation for
1830	* details on the usage of the next variable.
1831	*/
1832	arrived_in_time = blk_time_get_ns() <=
1833	bfqq->ttime.last_end_request +
1834	bfqd->bfq_slice_idle * 3;
1835	unsigned int act_idx = bfq_actuator_index(bfqd, bio: rq->bio);
1836	bool bfqq_non_merged_or_stably_merged =
1837	bfqq->bic || RQ_BIC(rq)->bfqq_data[act_idx].stably_merged;
1838
1839	/*
1840	* bfqq deserves to be weight-raised if:
1841	* - it is sync,
1842	* - it does not belong to a large burst,
1843	* - it has been idle for enough time or is soft real-time,
1844	* - is linked to a bfq_io_cq (it is not shared in any sense),
1845	* - has a default weight (otherwise we assume the user wanted
1846	* to control its weight explicitly)
1847	*/
1848	in_burst = bfq_bfqq_in_large_burst(bfqq);
1849	soft_rt = bfqd->bfq_wr_max_softrt_rate > 0 &&
1850	!BFQQ_TOTALLY_SEEKY(bfqq) &&
1851	!in_burst &&
1852	time_is_before_jiffies(bfqq->soft_rt_next_start) &&
1853	bfqq->dispatched == 0 &&
1854	bfqq->entity.new_weight == 40;
1855	*interactive = !in_burst && idle_for_long_time &&
1856	bfqq->entity.new_weight == 40;
1857	/*
1858	* Merged bfq_queues are kept out of weight-raising
1859	* (low-latency) mechanisms. The reason is that these queues
1860	* are usually created for non-interactive and
1861	* non-soft-real-time tasks. Yet this is not the case for
1862	* stably-merged queues. These queues are merged just because
1863	* they are created shortly after each other. So they may
1864	* easily serve the I/O of an interactive or soft-real time
1865	* application, if the application happens to spawn multiple
1866	* processes. So let also stably-merged queued enjoy weight
1867	* raising.
1868	*/
1869	wr_or_deserves_wr = bfqd->low_latency &&
1870	(bfqq->wr_coeff > 1 ||
1871	(bfq_bfqq_sync(bfqq) && bfqq_non_merged_or_stably_merged &&
1872	(*interactive || soft_rt)));
1873
1874	/*
1875	* Using the last flag, update budget and check whether bfqq
1876	* may want to preempt the in-service queue.
1877	*/
1878	bfqq_wants_to_preempt =
1879	bfq_bfqq_update_budg_for_activation(bfqd, bfqq,
1880	arrived_in_time);
1881
1882	/*
1883	* If bfqq happened to be activated in a burst, but has been
1884	* idle for much more than an interactive queue, then we
1885	* assume that, in the overall I/O initiated in the burst, the
1886	* I/O associated with bfqq is finished. So bfqq does not need
1887	* to be treated as a queue belonging to a burst
1888	* anymore. Accordingly, we reset bfqq's in_large_burst flag
1889	* if set, and remove bfqq from the burst list if it's
1890	* there. We do not decrement burst_size, because the fact
1891	* that bfqq does not need to belong to the burst list any
1892	* more does not invalidate the fact that bfqq was created in
1893	* a burst.
1894	*/
1895	if (likely(!bfq_bfqq_just_created(bfqq)) &&
1896	idle_for_long_time &&
1897	time_is_before_jiffies(
1898	bfqq->budget_timeout +
1899	msecs_to_jiffies(10000))) {
1900	hlist_del_init(n: &bfqq->burst_list_node);
1901	bfq_clear_bfqq_in_large_burst(bfqq);
1902	}
1903
1904	bfq_clear_bfqq_just_created(bfqq);
1905
1906	if (bfqd->low_latency) {
1907	if (unlikely(time_is_after_jiffies(bfqq->split_time)))
1908	/* wraparound */
1909	bfqq->split_time =
1910	jiffies - bfqd->bfq_wr_min_idle_time - 1;
1911
1912	if (time_is_before_jiffies(bfqq->split_time +
1913	bfqd->bfq_wr_min_idle_time)) {
1914	bfq_update_bfqq_wr_on_rq_arrival(bfqd, bfqq,
1915	old_wr_coeff,
1916	wr_or_deserves_wr,
1917	interactive: *interactive,
1918	in_burst,
1919	soft_rt);
1920
1921	if (old_wr_coeff != bfqq->wr_coeff)
1922	bfqq->entity.prio_changed = 1;
1923	}
1924	}
1925
1926	bfqq->last_idle_bklogged = jiffies;
1927	bfqq->service_from_backlogged = 0;
1928	bfq_clear_bfqq_softrt_update(bfqq);
1929
1930	bfq_add_bfqq_busy(bfqq);
1931
1932	/*
1933	* Expire in-service queue if preemption may be needed for
1934	* guarantees or throughput. As for guarantees, we care
1935	* explicitly about two cases. The first is that bfqq has to
1936	* recover a service hole, as explained in the comments on
1937	* bfq_bfqq_update_budg_for_activation(), i.e., that
1938	* bfqq_wants_to_preempt is true. However, if bfqq does not
1939	* carry time-critical I/O, then bfqq's bandwidth is less
1940	* important than that of queues that carry time-critical I/O.
1941	* So, as a further constraint, we consider this case only if
1942	* bfqq is at least as weight-raised, i.e., at least as time
1943	* critical, as the in-service queue.
1944	*
1945	* The second case is that bfqq is in a higher priority class,
1946	* or has a higher weight than the in-service queue. If this
1947	* condition does not hold, we don't care because, even if
1948	* bfqq does not start to be served immediately, the resulting
1949	* delay for bfqq's I/O is however lower or much lower than
1950	* the ideal completion time to be guaranteed to bfqq's I/O.
1951	*
1952	* In both cases, preemption is needed only if, according to
1953	* the timestamps of both bfqq and of the in-service queue,
1954	* bfqq actually is the next queue to serve. So, to reduce
1955	* useless preemptions, the return value of
1956	* next_queue_may_preempt() is considered in the next compound
1957	* condition too. Yet next_queue_may_preempt() just checks a
1958	* simple, necessary condition for bfqq to be the next queue
1959	* to serve. In fact, to evaluate a sufficient condition, the
1960	* timestamps of the in-service queue would need to be
1961	* updated, and this operation is quite costly (see the
1962	* comments on bfq_bfqq_update_budg_for_activation()).
1963	*
1964	* As for throughput, we ask bfq_better_to_idle() whether we
1965	* still need to plug I/O dispatching. If bfq_better_to_idle()
1966	* says no, then plugging is not needed any longer, either to
1967	* boost throughput or to perserve service guarantees. Then
1968	* the best option is to stop plugging I/O, as not doing so
1969	* would certainly lower throughput. We may end up in this
1970	* case if: (1) upon a dispatch attempt, we detected that it
1971	* was better to plug I/O dispatch, and to wait for a new
1972	* request to arrive for the currently in-service queue, but
1973	* (2) this switch of bfqq to busy changes the scenario.
1974	*/
1975	if (bfqd->in_service_queue &&
1976	((bfqq_wants_to_preempt &&
1977	bfqq->wr_coeff >= bfqd->in_service_queue->wr_coeff) ||
1978	bfq_bfqq_higher_class_or_weight(bfqq, in_serv_bfqq: bfqd->in_service_queue) ||
1979	!bfq_better_to_idle(bfqq: bfqd->in_service_queue)) &&
1980	next_queue_may_preempt(bfqd))
1981	bfq_bfqq_expire(bfqd, bfqq: bfqd->in_service_queue,
1982	compensate: false, reason: BFQQE_PREEMPTED);
1983	}
1984
1985	static void bfq_reset_inject_limit(struct bfq_data *bfqd,
1986	struct bfq_queue *bfqq)
1987	{
1988	/* invalidate baseline total service time */
1989	bfqq->last_serv_time_ns = 0;
1990
1991	/*
1992	* Reset pointer in case we are waiting for
1993	* some request completion.
1994	*/
1995	bfqd->waited_rq = NULL;
1996
1997	/*
1998	* If bfqq has a short think time, then start by setting the
1999	* inject limit to 0 prudentially, because the service time of
2000	* an injected I/O request may be higher than the think time
2001	* of bfqq, and therefore, if one request was injected when
2002	* bfqq remains empty, this injected request might delay the
2003	* service of the next I/O request for bfqq significantly. In
2004	* case bfqq can actually tolerate some injection, then the
2005	* adaptive update will however raise the limit soon. This
2006	* lucky circumstance holds exactly because bfqq has a short
2007	* think time, and thus, after remaining empty, is likely to
2008	* get new I/O enqueued---and then completed---before being
2009	* expired. This is the very pattern that gives the
2010	* limit-update algorithm the chance to measure the effect of
2011	* injection on request service times, and then to update the
2012	* limit accordingly.
2013	*
2014	* However, in the following special case, the inject limit is
2015	* left to 1 even if the think time is short: bfqq's I/O is
2016	* synchronized with that of some other queue, i.e., bfqq may
2017	* receive new I/O only after the I/O of the other queue is
2018	* completed. Keeping the inject limit to 1 allows the
2019	* blocking I/O to be served while bfqq is in service. And
2020	* this is very convenient both for bfqq and for overall
2021	* throughput, as explained in detail in the comments in
2022	* bfq_update_has_short_ttime().
2023	*
2024	* On the opposite end, if bfqq has a long think time, then
2025	* start directly by 1, because:
2026	* a) on the bright side, keeping at most one request in
2027	* service in the drive is unlikely to cause any harm to the
2028	* latency of bfqq's requests, as the service time of a single
2029	* request is likely to be lower than the think time of bfqq;
2030	* b) on the downside, after becoming empty, bfqq is likely to
2031	* expire before getting its next request. With this request
2032	* arrival pattern, it is very hard to sample total service
2033	* times and update the inject limit accordingly (see comments
2034	* on bfq_update_inject_limit()). So the limit is likely to be
2035	* never, or at least seldom, updated. As a consequence, by
2036	* setting the limit to 1, we avoid that no injection ever
2037	* occurs with bfqq. On the downside, this proactive step
2038	* further reduces chances to actually compute the baseline
2039	* total service time. Thus it reduces chances to execute the
2040	* limit-update algorithm and possibly raise the limit to more
2041	* than 1.
2042	*/
2043	if (bfq_bfqq_has_short_ttime(bfqq))
2044	bfqq->inject_limit = 0;
2045	else
2046	bfqq->inject_limit = 1;
2047
2048	bfqq->decrease_time_jif = jiffies;
2049	}
2050
2051	static void bfq_update_io_intensity(struct bfq_queue *bfqq, u64 now_ns)
2052	{
2053	u64 tot_io_time = now_ns - bfqq->io_start_time;
2054
2055	if (RB_EMPTY_ROOT(&bfqq->sort_list) && bfqq->dispatched == 0)
2056	bfqq->tot_idle_time +=
2057	now_ns - bfqq->ttime.last_end_request;
2058
2059	if (unlikely(bfq_bfqq_just_created(bfqq)))
2060	return;
2061
2062	/*
2063	* Must be busy for at least about 80% of the time to be
2064	* considered I/O bound.
2065	*/
2066	if (bfqq->tot_idle_time * 5 > tot_io_time)
2067	bfq_clear_bfqq_IO_bound(bfqq);
2068	else
2069	bfq_mark_bfqq_IO_bound(bfqq);
2070
2071	/*
2072	* Keep an observation window of at most 200 ms in the past
2073	* from now.
2074	*/
2075	if (tot_io_time > 200 * NSEC_PER_MSEC) {
2076	bfqq->io_start_time = now_ns - (tot_io_time>>1);
2077	bfqq->tot_idle_time >>= 1;
2078	}
2079	}
2080
2081	/*
2082	* Detect whether bfqq's I/O seems synchronized with that of some
2083	* other queue, i.e., whether bfqq, after remaining empty, happens to
2084	* receive new I/O only right after some I/O request of the other
2085	* queue has been completed. We call waker queue the other queue, and
2086	* we assume, for simplicity, that bfqq may have at most one waker
2087	* queue.
2088	*
2089	* A remarkable throughput boost can be reached by unconditionally
2090	* injecting the I/O of the waker queue, every time a new
2091	* bfq_dispatch_request happens to be invoked while I/O is being
2092	* plugged for bfqq. In addition to boosting throughput, this
2093	* unblocks bfqq's I/O, thereby improving bandwidth and latency for
2094	* bfqq. Note that these same results may be achieved with the general
2095	* injection mechanism, but less effectively. For details on this
2096	* aspect, see the comments on the choice of the queue for injection
2097	* in bfq_select_queue().
2098	*
2099	* Turning back to the detection of a waker queue, a queue Q is deemed as a
2100	* waker queue for bfqq if, for three consecutive times, bfqq happens to become
2101	* non empty right after a request of Q has been completed within given
2102	* timeout. In this respect, even if bfqq is empty, we do not check for a waker
2103	* if it still has some in-flight I/O. In fact, in this case bfqq is actually
2104	* still being served by the drive, and may receive new I/O on the completion
2105	* of some of the in-flight requests. In particular, on the first time, Q is
2106	* tentatively set as a candidate waker queue, while on the third consecutive
2107	* time that Q is detected, the field waker_bfqq is set to Q, to confirm that Q
2108	* is a waker queue for bfqq. These detection steps are performed only if bfqq
2109	* has a long think time, so as to make it more likely that bfqq's I/O is
2110	* actually being blocked by a synchronization. This last filter, plus the
2111	* above three-times requirement and time limit for detection, make false
2112	* positives less likely.
2113	*
2114	* NOTE
2115	*
2116	* The sooner a waker queue is detected, the sooner throughput can be
2117	* boosted by injecting I/O from the waker queue. Fortunately,
2118	* detection is likely to be actually fast, for the following
2119	* reasons. While blocked by synchronization, bfqq has a long think
2120	* time. This implies that bfqq's inject limit is at least equal to 1
2121	* (see the comments in bfq_update_inject_limit()). So, thanks to
2122	* injection, the waker queue is likely to be served during the very
2123	* first I/O-plugging time interval for bfqq. This triggers the first
2124	* step of the detection mechanism. Thanks again to injection, the
2125	* candidate waker queue is then likely to be confirmed no later than
2126	* during the next I/O-plugging interval for bfqq.
2127	*
2128	* ISSUE
2129	*
2130	* On queue merging all waker information is lost.
2131	*/
2132	static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2133	u64 now_ns)
2134	{
2135	char waker_name[MAX_BFQQ_NAME_LENGTH];
2136
2137	if (!bfqd->last_completed_rq_bfqq ||
2138	bfqd->last_completed_rq_bfqq == bfqq ||
2139	bfq_bfqq_has_short_ttime(bfqq) ||
2140	now_ns - bfqd->last_completion >= 4 * NSEC_PER_MSEC ||
2141	bfqd->last_completed_rq_bfqq == &bfqd->oom_bfqq ||
2142	bfqq == &bfqd->oom_bfqq)
2143	return;
2144
2145	/*
2146	* We reset waker detection logic also if too much time has passed
2147	* since the first detection. If wakeups are rare, pointless idling
2148	* doesn't hurt throughput that much. The condition below makes sure
2149	* we do not uselessly idle blocking waker in more than 1/64 cases.
2150	*/
2151	if (bfqd->last_completed_rq_bfqq !=
2152	bfqq->tentative_waker_bfqq ||
2153	now_ns > bfqq->waker_detection_started +
2154	128 * (u64)bfqd->bfq_slice_idle) {
2155	/*
2156	* First synchronization detected with a
2157	* candidate waker queue, or with a different
2158	* candidate waker queue from the current one.
2159	*/
2160	bfqq->tentative_waker_bfqq =
2161	bfqd->last_completed_rq_bfqq;
2162	bfqq->num_waker_detections = 1;
2163	bfqq->waker_detection_started = now_ns;
2164	bfq_bfqq_name(bfqq: bfqq->tentative_waker_bfqq, str: waker_name,
2165	MAX_BFQQ_NAME_LENGTH);
2166	bfq_log_bfqq(bfqd, bfqq, "set tentative waker %s", waker_name);
2167	} else /* Same tentative waker queue detected again */
2168	bfqq->num_waker_detections++;
2169
2170	if (bfqq->num_waker_detections == 3) {
2171	bfqq->waker_bfqq = bfqd->last_completed_rq_bfqq;
2172	bfqq->tentative_waker_bfqq = NULL;
2173	bfq_bfqq_name(bfqq: bfqq->waker_bfqq, str: waker_name,
2174	MAX_BFQQ_NAME_LENGTH);
2175	bfq_log_bfqq(bfqd, bfqq, "set waker %s", waker_name);
2176
2177	/*
2178	* If the waker queue disappears, then
2179	* bfqq->waker_bfqq must be reset. To
2180	* this goal, we maintain in each
2181	* waker queue a list, woken_list, of
2182	* all the queues that reference the
2183	* waker queue through their
2184	* waker_bfqq pointer. When the waker
2185	* queue exits, the waker_bfqq pointer
2186	* of all the queues in the woken_list
2187	* is reset.
2188	*
2189	* In addition, if bfqq is already in
2190	* the woken_list of a waker queue,
2191	* then, before being inserted into
2192	* the woken_list of a new waker
2193	* queue, bfqq must be removed from
2194	* the woken_list of the old waker
2195	* queue.
2196	*/
2197	if (!hlist_unhashed(h: &bfqq->woken_list_node))
2198	hlist_del_init(n: &bfqq->woken_list_node);
2199	hlist_add_head(n: &bfqq->woken_list_node,
2200	h: &bfqd->last_completed_rq_bfqq->woken_list);
2201	}
2202	}
2203
2204	static void bfq_add_request(struct request *rq)
2205	{
2206	struct bfq_queue *bfqq = RQ_BFQQ(rq);
2207	struct bfq_data *bfqd = bfqq->bfqd;
2208	struct request *next_rq, *prev;
2209	unsigned int old_wr_coeff = bfqq->wr_coeff;
2210	bool interactive = false;
2211	u64 now_ns = blk_time_get_ns();
2212
2213	bfq_log_bfqq(bfqd, bfqq, "add_request %d", rq_is_sync(rq));
2214	bfqq->queued[rq_is_sync(rq)]++;
2215	/*
2216	* Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2217	* may be read without holding the lock in bfq_has_work().
2218	*/
2219	WRITE_ONCE(bfqd->queued, bfqd->queued + 1);
2220
2221	if (bfq_bfqq_sync(bfqq) && RQ_BIC(rq)->requests <= 1) {
2222	bfq_check_waker(bfqd, bfqq, now_ns);
2223
2224	/*
2225	* Periodically reset inject limit, to make sure that
2226	* the latter eventually drops in case workload
2227	* changes, see step (3) in the comments on
2228	* bfq_update_inject_limit().
2229	*/
2230	if (time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2231	msecs_to_jiffies(1000)))
2232	bfq_reset_inject_limit(bfqd, bfqq);
2233
2234	/*
2235	* The following conditions must hold to setup a new
2236	* sampling of total service time, and then a new
2237	* update of the inject limit:
2238	* - bfqq is in service, because the total service
2239	* time is evaluated only for the I/O requests of
2240	* the queues in service;
2241	* - this is the right occasion to compute or to
2242	* lower the baseline total service time, because
2243	* there are actually no requests in the drive,
2244	* or
2245	* the baseline total service time is available, and
2246	* this is the right occasion to compute the other
2247	* quantity needed to update the inject limit, i.e.,
2248	* the total service time caused by the amount of
2249	* injection allowed by the current value of the
2250	* limit. It is the right occasion because injection
2251	* has actually been performed during the service
2252	* hole, and there are still in-flight requests,
2253	* which are very likely to be exactly the injected
2254	* requests, or part of them;
2255	* - the minimum interval for sampling the total
2256	* service time and updating the inject limit has
2257	* elapsed.
2258	*/
2259	if (bfqq == bfqd->in_service_queue &&
2260	(bfqd->tot_rq_in_driver == 0 ||
2261	(bfqq->last_serv_time_ns > 0 &&
2262	bfqd->rqs_injected && bfqd->tot_rq_in_driver > 0)) &&
2263	time_is_before_eq_jiffies(bfqq->decrease_time_jif +
2264	msecs_to_jiffies(10))) {
2265	bfqd->last_empty_occupied_ns = blk_time_get_ns();
2266	/*
2267	* Start the state machine for measuring the
2268	* total service time of rq: setting
2269	* wait_dispatch will cause bfqd->waited_rq to
2270	* be set when rq will be dispatched.
2271	*/
2272	bfqd->wait_dispatch = true;
2273	/*
2274	* If there is no I/O in service in the drive,
2275	* then possible injection occurred before the
2276	* arrival of rq will not affect the total
2277	* service time of rq. So the injection limit
2278	* must not be updated as a function of such
2279	* total service time, unless new injection
2280	* occurs before rq is completed. To have the
2281	* injection limit updated only in the latter
2282	* case, reset rqs_injected here (rqs_injected
2283	* will be set in case injection is performed
2284	* on bfqq before rq is completed).
2285	*/
2286	if (bfqd->tot_rq_in_driver == 0)
2287	bfqd->rqs_injected = false;
2288	}
2289	}
2290
2291	if (bfq_bfqq_sync(bfqq))
2292	bfq_update_io_intensity(bfqq, now_ns);
2293
2294	elv_rb_add(&bfqq->sort_list, rq);
2295
2296	/*
2297	* Check if this request is a better next-serve candidate.
2298	*/
2299	prev = bfqq->next_rq;
2300	next_rq = bfq_choose_req(bfqd, rq1: bfqq->next_rq, rq2: rq, last: bfqd->last_position);
2301	bfqq->next_rq = next_rq;
2302
2303	/*
2304	* Adjust priority tree position, if next_rq changes.
2305	* See comments on bfq_pos_tree_add_move() for the unlikely().
2306	*/
2307	if (unlikely(!bfqd->nonrot_with_queueing && prev != bfqq->next_rq))
2308	bfq_pos_tree_add_move(bfqd, bfqq);
2309
2310	if (!bfq_bfqq_busy(bfqq)) /* switching to busy ... */
2311	bfq_bfqq_handle_idle_busy_switch(bfqd, bfqq, old_wr_coeff,
2312	rq, interactive: &interactive);
2313	else {
2314	if (bfqd->low_latency && old_wr_coeff == 1 && !rq_is_sync(rq) &&
2315	time_is_before_jiffies(
2316	bfqq->last_wr_start_finish +
2317	bfqd->bfq_wr_min_inter_arr_async)) {
2318	bfqq->wr_coeff = bfqd->bfq_wr_coeff;
2319	bfqq->wr_cur_max_time = bfq_wr_duration(bfqd);
2320
2321	bfqd->wr_busy_queues++;
2322	bfqq->entity.prio_changed = 1;
2323	}
2324	if (prev != bfqq->next_rq)
2325	bfq_updated_next_req(bfqd, bfqq);
2326	}
2327
2328	/*
2329	* Assign jiffies to last_wr_start_finish in the following
2330	* cases:
2331	*
2332	* . if bfqq is not going to be weight-raised, because, for
2333	* non weight-raised queues, last_wr_start_finish stores the
2334	* arrival time of the last request; as of now, this piece
2335	* of information is used only for deciding whether to
2336	* weight-raise async queues
2337	*
2338	* . if bfqq is not weight-raised, because, if bfqq is now
2339	* switching to weight-raised, then last_wr_start_finish
2340	* stores the time when weight-raising starts
2341	*
2342	* . if bfqq is interactive, because, regardless of whether
2343	* bfqq is currently weight-raised, the weight-raising
2344	* period must start or restart (this case is considered
2345	* separately because it is not detected by the above
2346	* conditions, if bfqq is already weight-raised)
2347	*
2348	* last_wr_start_finish has to be updated also if bfqq is soft
2349	* real-time, because the weight-raising period is constantly
2350	* restarted on idle-to-busy transitions for these queues, but
2351	* this is already done in bfq_bfqq_handle_idle_busy_switch if
2352	* needed.
2353	*/
2354	if (bfqd->low_latency &&
2355	(old_wr_coeff == 1 || bfqq->wr_coeff == 1 || interactive))
2356	bfqq->last_wr_start_finish = jiffies;
2357	}
2358
2359	static struct request *bfq_find_rq_fmerge(struct bfq_data *bfqd,
2360	struct bio *bio,
2361	struct request_queue *q)
2362	{
2363	struct bfq_queue *bfqq = bfqd->bio_bfqq;
2364
2365
2366	if (bfqq)
2367	return elv_rb_find(&bfqq->sort_list, bio_end_sector(bio));
2368
2369	return NULL;
2370	}
2371
2372	static sector_t get_sdist(sector_t last_pos, struct request *rq)
2373	{
2374	if (last_pos)
2375	return abs(blk_rq_pos(rq) - last_pos);
2376
2377	return 0;
2378	}
2379
2380	static void bfq_remove_request(struct request_queue *q,
2381	struct request *rq)
2382	{
2383	struct bfq_queue *bfqq = RQ_BFQQ(rq);
2384	struct bfq_data *bfqd = bfqq->bfqd;
2385	const int sync = rq_is_sync(rq);
2386
2387	if (bfqq->next_rq == rq) {
2388	bfqq->next_rq = bfq_find_next_rq(bfqd, bfqq, last: rq);
2389	bfq_updated_next_req(bfqd, bfqq);
2390	}
2391
2392	if (rq->queuelist.prev != &rq->queuelist)
2393	list_del_init(entry: &rq->queuelist);
2394	bfqq->queued[sync]--;
2395	/*
2396	* Updating of 'bfqd->queued' is protected by 'bfqd->lock', however, it
2397	* may be read without holding the lock in bfq_has_work().
2398	*/
2399	WRITE_ONCE(bfqd->queued, bfqd->queued - 1);
2400	elv_rb_del(&bfqq->sort_list, rq);
2401
2402	elv_rqhash_del(q, rq);
2403	if (q->last_merge == rq)
2404	q->last_merge = NULL;
2405
2406	if (RB_EMPTY_ROOT(&bfqq->sort_list)) {
2407	bfqq->next_rq = NULL;
2408
2409	if (bfq_bfqq_busy(bfqq) && bfqq != bfqd->in_service_queue) {
2410	bfq_del_bfqq_busy(bfqq, expiration: false);
2411	/*
2412	* bfqq emptied. In normal operation, when
2413	* bfqq is empty, bfqq->entity.service and
2414	* bfqq->entity.budget must contain,
2415	* respectively, the service received and the
2416	* budget used last time bfqq emptied. These
2417	* facts do not hold in this case, as at least
2418	* this last removal occurred while bfqq is
2419	* not in service. To avoid inconsistencies,
2420	* reset both bfqq->entity.service and
2421	* bfqq->entity.budget, if bfqq has still a
2422	* process that may issue I/O requests to it.
2423	*/
2424	bfqq->entity.budget = bfqq->entity.service = 0;
2425	}
2426
2427	/*
2428	* Remove queue from request-position tree as it is empty.
2429	*/
2430	if (bfqq->pos_root) {
2431	rb_erase(&bfqq->pos_node, bfqq->pos_root);
2432	bfqq->pos_root = NULL;
2433	}
2434	} else {
2435	/* see comments on bfq_pos_tree_add_move() for the unlikely() */
2436	if (unlikely(!bfqd->nonrot_with_queueing))
2437	bfq_pos_tree_add_move(bfqd, bfqq);
2438	}
2439
2440	if (rq->cmd_flags & REQ_META)
2441	bfqq->meta_pending--;
2442
2443	}
2444
2445	static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
2446	unsigned int nr_segs)
2447	{
2448	struct bfq_data *bfqd = q->elevator->elevator_data;
2449	struct request *free = NULL;
2450	/*
2451	* bfq_bic_lookup grabs the queue_lock: invoke it now and
2452	* store its return value for later use, to avoid nesting
2453	* queue_lock inside the bfqd->lock. We assume that the bic
2454	* returned by bfq_bic_lookup does not go away before
2455	* bfqd->lock is taken.
2456	*/
2457	struct bfq_io_cq *bic = bfq_bic_lookup(q);
2458	bool ret;
2459
2460	spin_lock_irq(lock: &bfqd->lock);
2461
2462	if (bic) {
2463	/*
2464	* Make sure cgroup info is uptodate for current process before
2465	* considering the merge.
2466	*/
2467	bfq_bic_update_cgroup(bic, bio);
2468
2469	bfqd->bio_bfqq = bic_to_bfqq(bic, is_sync: op_is_sync(op: bio->bi_opf),
2470	actuator_idx: bfq_actuator_index(bfqd, bio));
2471	} else {
2472	bfqd->bio_bfqq = NULL;
2473	}
2474	bfqd->bio_bic = bic;
2475
2476	ret = blk_mq_sched_try_merge(q, bio, nr_segs, merged_request: &free);
2477
2478	spin_unlock_irq(lock: &bfqd->lock);
2479	if (free)
2480	blk_mq_free_request(rq: free);
2481
2482	return ret;
2483	}
2484
2485	static int bfq_request_merge(struct request_queue *q, struct request **req,
2486	struct bio *bio)
2487	{
2488	struct bfq_data *bfqd = q->elevator->elevator_data;
2489	struct request *__rq;
2490
2491	__rq = bfq_find_rq_fmerge(bfqd, bio, q);
2492	if (__rq && elv_bio_merge_ok(__rq, bio)) {
2493	*req = __rq;
2494
2495	if (blk_discard_mergable(req: __rq))
2496	return ELEVATOR_DISCARD_MERGE;
2497	return ELEVATOR_FRONT_MERGE;
2498	}
2499
2500	return ELEVATOR_NO_MERGE;
2501	}
2502
2503	static void bfq_request_merged(struct request_queue *q, struct request *req,
2504	enum elv_merge type)
2505	{
2506	if (type == ELEVATOR_FRONT_MERGE &&
2507	rb_prev(&req->rb_node) &&
2508	blk_rq_pos(rq: req) <
2509	blk_rq_pos(container_of(rb_prev(&req->rb_node),
2510	struct request, rb_node))) {
2511	struct bfq_queue *bfqq = RQ_BFQQ(req);
2512	struct bfq_data *bfqd;
2513	struct request *prev, *next_rq;
2514
2515	if (!bfqq)
2516	return;
2517
2518	bfqd = bfqq->bfqd;
2519
2520	/* Reposition request in its sort_list */
2521	elv_rb_del(&bfqq->sort_list, req);
2522	elv_rb_add(&bfqq->sort_list, req);
2523
2524	/* Choose next request to be served for bfqq */
2525	prev = bfqq->next_rq;
2526	next_rq = bfq_choose_req(bfqd, rq1: bfqq->next_rq, rq2: req,
2527	last: bfqd->last_position);
2528	bfqq->next_rq = next_rq;
2529	/*
2530	* If next_rq changes, update both the queue's budget to
2531	* fit the new request and the queue's position in its
2532	* rq_pos_tree.
2533	*/
2534	if (prev != bfqq->next_rq) {
2535	bfq_updated_next_req(bfqd, bfqq);
2536	/*
2537	* See comments on bfq_pos_tree_add_move() for
2538	* the unlikely().
2539	*/
2540	if (unlikely(!bfqd->nonrot_with_queueing))
2541	bfq_pos_tree_add_move(bfqd, bfqq);
2542	}
2543	}
2544	}
2545
2546	/*
2547	* This function is called to notify the scheduler that the requests
2548	* rq and 'next' have been merged, with 'next' going away. BFQ
2549	* exploits this hook to address the following issue: if 'next' has a
2550	* fifo_time lower that rq, then the fifo_time of rq must be set to
2551	* the value of 'next', to not forget the greater age of 'next'.
2552	*
2553	* NOTE: in this function we assume that rq is in a bfq_queue, basing
2554	* on that rq is picked from the hash table q->elevator->hash, which,
2555	* in its turn, is filled only with I/O requests present in
2556	* bfq_queues, while BFQ is in use for the request queue q. In fact,
2557	* the function that fills this hash table (elv_rqhash_add) is called
2558	* only by bfq_insert_request.
2559	*/
2560	static void bfq_requests_merged(struct request_queue *q, struct request *rq,
2561	struct request *next)
2562	{
2563	struct bfq_queue *bfqq = RQ_BFQQ(rq),
2564	*next_bfqq = RQ_BFQQ(next);
2565
2566	if (!bfqq)
2567	goto remove;
2568
2569	/*
2570	* If next and rq belong to the same bfq_queue and next is older
2571	* than rq, then reposition rq in the fifo (by substituting next
2572	* with rq). Otherwise, if next and rq belong to different
2573	* bfq_queues, never reposition rq: in fact, we would have to
2574	* reposition it with respect to next's position in its own fifo,
2575	* which would most certainly be too expensive with respect to
2576	* the benefits.
2577	*/
2578	if (bfqq == next_bfqq &&
2579	!list_empty(head: &rq->queuelist) && !list_empty(head: &next->queuelist) &&
2580	next->fifo_time < rq->fifo_time) {
2581	list_del_init(entry: &rq->queuelist);
2582	list_replace_init(old: &next->queuelist, new: &rq->queuelist);
2583	rq->fifo_time = next->fifo_time;
2584	}
2585
2586	if (bfqq->next_rq == next)
2587	bfqq->next_rq = rq;
2588
2589	bfqg_stats_update_io_merged(bfqg: bfqq_group(bfqq), opf: next->cmd_flags);
2590	remove:
2591	/* Merged request may be in the IO scheduler. Remove it. */
2592	if (!RB_EMPTY_NODE(&next->rb_node)) {
2593	bfq_remove_request(q: next->q, rq: next);
2594	if (next_bfqq)
2595	bfqg_stats_update_io_remove(bfqg: bfqq_group(bfqq: next_bfqq),
2596	opf: next->cmd_flags);
2597	}
2598	}
2599
2600	/* Must be called with bfqq != NULL */
2601	static void bfq_bfqq_end_wr(struct bfq_queue *bfqq)
2602	{
2603	/*
2604	* If bfqq has been enjoying interactive weight-raising, then
2605	* reset soft_rt_next_start. We do it for the following
2606	* reason. bfqq may have been conveying the I/O needed to load
2607	* a soft real-time application. Such an application actually
2608	* exhibits a soft real-time I/O pattern after it finishes
2609	* loading, and finally starts doing its job. But, if bfqq has
2610	* been receiving a lot of bandwidth so far (likely to happen
2611	* on a fast device), then soft_rt_next_start now contains a
2612	* high value that. So, without this reset, bfqq would be
2613	* prevented from being possibly considered as soft_rt for a
2614	* very long time.
2615	*/
2616
2617	if (bfqq->wr_cur_max_time !=
2618	bfqq->bfqd->bfq_wr_rt_max_time)
2619	bfqq->soft_rt_next_start = jiffies;
2620
2621	if (bfq_bfqq_busy(bfqq))
2622	bfqq->bfqd->wr_busy_queues--;
2623	bfqq->wr_coeff = 1;
2624	bfqq->wr_cur_max_time = 0;
2625	bfqq->last_wr_start_finish = jiffies;
2626	/*
2627	* Trigger a weight change on the next invocation of
2628	* __bfq_entity_update_weight_prio.
2629	*/
2630	bfqq->entity.prio_changed = 1;
2631	}
2632
2633	void bfq_end_wr_async_queues(struct bfq_data *bfqd,
2634	struct bfq_group *bfqg)
2635	{
2636	int i, j, k;
2637
2638	for (k = 0; k < bfqd->num_actuators; k++) {
2639	for (i = 0; i < 2; i++)
2640	for (j = 0; j < IOPRIO_NR_LEVELS; j++)
2641	if (bfqg->async_bfqq[i][j][k])
2642	bfq_bfqq_end_wr(bfqq: bfqg->async_bfqq[i][j][k]);
2643	if (bfqg->async_idle_bfqq[k])
2644	bfq_bfqq_end_wr(bfqq: bfqg->async_idle_bfqq[k]);
2645	}
2646	}
2647
2648	static void bfq_end_wr(struct bfq_data *bfqd)
2649	{
2650	struct bfq_queue *bfqq;
2651	int i;
2652
2653	spin_lock_irq(lock: &bfqd->lock);
2654
2655	for (i = 0; i < bfqd->num_actuators; i++) {
2656	list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
2657	bfq_bfqq_end_wr(bfqq);
2658	}
2659	list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
2660	bfq_bfqq_end_wr(bfqq);
2661	bfq_end_wr_async(bfqd);
2662
2663	spin_unlock_irq(lock: &bfqd->lock);
2664	}
2665
2666	static sector_t bfq_io_struct_pos(void *io_struct, bool request)
2667	{
2668	if (request)
2669	return blk_rq_pos(rq: io_struct);
2670	else
2671	return ((struct bio *)io_struct)->bi_iter.bi_sector;
2672	}
2673
2674	static int bfq_rq_close_to_sector(void *io_struct, bool request,
2675	sector_t sector)
2676	{
2677	return abs(bfq_io_struct_pos(io_struct, request) - sector) <=
2678	BFQQ_CLOSE_THR;
2679	}
2680
2681	static struct bfq_queue *bfqq_find_close(struct bfq_data *bfqd,
2682	struct bfq_queue *bfqq,
2683	sector_t sector)
2684	{
2685	struct rb_root *root = &bfqq_group(bfqq)->rq_pos_tree;
2686	struct rb_node *parent, *node;
2687	struct bfq_queue *__bfqq;
2688
2689	if (RB_EMPTY_ROOT(root))
2690	return NULL;
2691
2692	/*
2693	* First, if we find a request starting at the end of the last
2694	* request, choose it.
2695	*/
2696	__bfqq = bfq_rq_pos_tree_lookup(bfqd, root, sector, ret_parent: &parent, NULL);
2697	if (__bfqq)
2698	return __bfqq;
2699
2700	/*
2701	* If the exact sector wasn't found, the parent of the NULL leaf
2702	* will contain the closest sector (rq_pos_tree sorted by
2703	* next_request position).
2704	*/
2705	__bfqq = rb_entry(parent, struct bfq_queue, pos_node);
2706	if (bfq_rq_close_to_sector(io_struct: __bfqq->next_rq, request: true, sector))
2707	return __bfqq;
2708
2709	if (blk_rq_pos(rq: __bfqq->next_rq) < sector)
2710	node = rb_next(&__bfqq->pos_node);
2711	else
2712	node = rb_prev(&__bfqq->pos_node);
2713	if (!node)
2714	return NULL;
2715
2716	__bfqq = rb_entry(node, struct bfq_queue, pos_node);
2717	if (bfq_rq_close_to_sector(io_struct: __bfqq->next_rq, request: true, sector))
2718	return __bfqq;
2719
2720	return NULL;
2721	}
2722
2723	static struct bfq_queue *bfq_find_close_cooperator(struct bfq_data *bfqd,
2724	struct bfq_queue *cur_bfqq,
2725	sector_t sector)
2726	{
2727	struct bfq_queue *bfqq;
2728
2729	/*
2730	* We shall notice if some of the queues are cooperating,
2731	* e.g., working closely on the same area of the device. In
2732	* that case, we can group them together and: 1) don't waste
2733	* time idling, and 2) serve the union of their requests in
2734	* the best possible order for throughput.
2735	*/
2736	bfqq = bfqq_find_close(bfqd, bfqq: cur_bfqq, sector);
2737	if (!bfqq || bfqq == cur_bfqq)
2738	return NULL;
2739
2740	return bfqq;
2741	}
2742
2743	static struct bfq_queue *
2744	bfq_setup_merge(struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
2745	{
2746	int process_refs, new_process_refs;
2747	struct bfq_queue *__bfqq;
2748
2749	/*
2750	* If there are no process references on the new_bfqq, then it is
2751	* unsafe to follow the ->new_bfqq chain as other bfqq's in the chain
2752	* may have dropped their last reference (not just their last process
2753	* reference).
2754	*/
2755	if (!bfqq_process_refs(bfqq: new_bfqq))
2756	return NULL;
2757
2758	/* Avoid a circular list and skip interim queue merges. */
2759	while ((__bfqq = new_bfqq->new_bfqq)) {
2760	if (__bfqq == bfqq)
2761	return NULL;
2762	new_bfqq = __bfqq;
2763	}
2764
2765	process_refs = bfqq_process_refs(bfqq);
2766	new_process_refs = bfqq_process_refs(bfqq: new_bfqq);
2767	/*
2768	* If the process for the bfqq has gone away, there is no
2769	* sense in merging the queues.
2770	*/
2771	if (process_refs == 0 || new_process_refs == 0)
2772	return NULL;
2773
2774	/*
2775	* Make sure merged queues belong to the same parent. Parents could
2776	* have changed since the time we decided the two queues are suitable
2777	* for merging.
2778	*/
2779	if (new_bfqq->entity.parent != bfqq->entity.parent)
2780	return NULL;
2781
2782	bfq_log_bfqq(bfqq->bfqd, bfqq, "scheduling merge with queue %d",
2783	new_bfqq->pid);
2784
2785	/*
2786	* Merging is just a redirection: the requests of the process
2787	* owning one of the two queues are redirected to the other queue.
2788	* The latter queue, in its turn, is set as shared if this is the
2789	* first time that the requests of some process are redirected to
2790	* it.
2791	*
2792	* We redirect bfqq to new_bfqq and not the opposite, because
2793	* we are in the context of the process owning bfqq, thus we
2794	* have the io_cq of this process. So we can immediately
2795	* configure this io_cq to redirect the requests of the
2796	* process to new_bfqq. In contrast, the io_cq of new_bfqq is
2797	* not available any more (new_bfqq->bic == NULL).
2798	*
2799	* Anyway, even in case new_bfqq coincides with the in-service
2800	* queue, redirecting requests the in-service queue is the
2801	* best option, as we feed the in-service queue with new
2802	* requests close to the last request served and, by doing so,
2803	* are likely to increase the throughput.
2804	*/
2805	bfqq->new_bfqq = new_bfqq;
2806	/*
2807	* The above assignment schedules the following redirections:
2808	* each time some I/O for bfqq arrives, the process that
2809	* generated that I/O is disassociated from bfqq and
2810	* associated with new_bfqq. Here we increases new_bfqq->ref
2811	* in advance, adding the number of processes that are
2812	* expected to be associated with new_bfqq as they happen to
2813	* issue I/O.
2814	*/
2815	new_bfqq->ref += process_refs;
2816	return new_bfqq;
2817	}
2818
2819	static bool bfq_may_be_close_cooperator(struct bfq_queue *bfqq,
2820	struct bfq_queue *new_bfqq)
2821	{
2822	if (bfq_too_late_for_merging(bfqq: new_bfqq))
2823	return false;
2824
2825	if (bfq_class_idle(bfqq) || bfq_class_idle(new_bfqq) ||
2826	(bfqq->ioprio_class != new_bfqq->ioprio_class))
2827	return false;
2828
2829	/*
2830	* If either of the queues has already been detected as seeky,
2831	* then merging it with the other queue is unlikely to lead to
2832	* sequential I/O.
2833	*/
2834	if (BFQQ_SEEKY(bfqq) || BFQQ_SEEKY(new_bfqq))
2835	return false;
2836
2837	/*
2838	* Interleaved I/O is known to be done by (some) applications
2839	* only for reads, so it does not make sense to merge async
2840	* queues.
2841	*/
2842	if (!bfq_bfqq_sync(bfqq) || !bfq_bfqq_sync(bfqq: new_bfqq))
2843	return false;
2844
2845	return true;
2846	}
2847
2848	static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
2849	struct bfq_queue *bfqq);
2850
2851	static struct bfq_queue *
2852	bfq_setup_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2853	struct bfq_queue *stable_merge_bfqq,
2854	struct bfq_iocq_bfqq_data *bfqq_data)
2855	{
2856	int proc_ref = min(bfqq_process_refs(bfqq),
2857	bfqq_process_refs(stable_merge_bfqq));
2858	struct bfq_queue *new_bfqq = NULL;
2859
2860	bfqq_data->stable_merge_bfqq = NULL;
2861	if (idling_boosts_thr_without_issues(bfqd, bfqq) || proc_ref == 0)
2862	goto out;
2863
2864	/* next function will take at least one ref */
2865	new_bfqq = bfq_setup_merge(bfqq, new_bfqq: stable_merge_bfqq);
2866
2867	if (new_bfqq) {
2868	bfqq_data->stably_merged = true;
2869	if (new_bfqq->bic) {
2870	unsigned int new_a_idx = new_bfqq->actuator_idx;
2871	struct bfq_iocq_bfqq_data *new_bfqq_data =
2872	&new_bfqq->bic->bfqq_data[new_a_idx];
2873
2874	new_bfqq_data->stably_merged = true;
2875	}
2876	}
2877
2878	out:
2879	/* deschedule stable merge, because done or aborted here */
2880	bfq_put_stable_ref(bfqq: stable_merge_bfqq);
2881
2882	return new_bfqq;
2883	}
2884
2885	/*
2886	* Attempt to schedule a merge of bfqq with the currently in-service
2887	* queue or with a close queue among the scheduled queues. Return
2888	* NULL if no merge was scheduled, a pointer to the shared bfq_queue
2889	* structure otherwise.
2890	*
2891	* The OOM queue is not allowed to participate to cooperation: in fact, since
2892	* the requests temporarily redirected to the OOM queue could be redirected
2893	* again to dedicated queues at any time, the state needed to correctly
2894	* handle merging with the OOM queue would be quite complex and expensive
2895	* to maintain. Besides, in such a critical condition as an out of memory,
2896	* the benefits of queue merging may be little relevant, or even negligible.
2897	*
2898	* WARNING: queue merging may impair fairness among non-weight raised
2899	* queues, for at least two reasons: 1) the original weight of a
2900	* merged queue may change during the merged state, 2) even being the
2901	* weight the same, a merged queue may be bloated with many more
2902	* requests than the ones produced by its originally-associated
2903	* process.
2904	*/
2905	static struct bfq_queue *
2906	bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
2907	void *io_struct, bool request, struct bfq_io_cq *bic)
2908	{
2909	struct bfq_queue *in_service_bfqq, *new_bfqq;
2910	unsigned int a_idx = bfqq->actuator_idx;
2911	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
2912
2913	/* if a merge has already been setup, then proceed with that first */
2914	if (bfqq->new_bfqq)
2915	return bfqq->new_bfqq;
2916
2917	/*
2918	* Check delayed stable merge for rotational or non-queueing
2919	* devs. For this branch to be executed, bfqq must not be
2920	* currently merged with some other queue (i.e., bfqq->bic
2921	* must be non null). If we considered also merged queues,
2922	* then we should also check whether bfqq has already been
2923	* merged with bic->stable_merge_bfqq. But this would be
2924	* costly and complicated.
2925	*/
2926	if (unlikely(!bfqd->nonrot_with_queueing)) {
2927	/*
2928	* Make sure also that bfqq is sync, because
2929	* bic->stable_merge_bfqq may point to some queue (for
2930	* stable merging) also if bic is associated with a
2931	* sync queue, but this bfqq is async
2932	*/
2933	if (bfq_bfqq_sync(bfqq) && bfqq_data->stable_merge_bfqq &&
2934	!bfq_bfqq_just_created(bfqq) &&
2935	time_is_before_jiffies(bfqq->split_time +
2936	msecs_to_jiffies(bfq_late_stable_merging)) &&
2937	time_is_before_jiffies(bfqq->creation_time +
2938	msecs_to_jiffies(bfq_late_stable_merging))) {
2939	struct bfq_queue *stable_merge_bfqq =
2940	bfqq_data->stable_merge_bfqq;
2941
2942	return bfq_setup_stable_merge(bfqd, bfqq,
2943	stable_merge_bfqq,
2944	bfqq_data);
2945	}
2946	}
2947
2948	/*
2949	* Do not perform queue merging if the device is non
2950	* rotational and performs internal queueing. In fact, such a
2951	* device reaches a high speed through internal parallelism
2952	* and pipelining. This means that, to reach a high
2953	* throughput, it must have many requests enqueued at the same
2954	* time. But, in this configuration, the internal scheduling
2955	* algorithm of the device does exactly the job of queue
2956	* merging: it reorders requests so as to obtain as much as
2957	* possible a sequential I/O pattern. As a consequence, with
2958	* the workload generated by processes doing interleaved I/O,
2959	* the throughput reached by the device is likely to be the
2960	* same, with and without queue merging.
2961	*
2962	* Disabling merging also provides a remarkable benefit in
2963	* terms of throughput. Merging tends to make many workloads
2964	* artificially more uneven, because of shared queues
2965	* remaining non empty for incomparably more time than
2966	* non-merged queues. This may accentuate workload
2967	* asymmetries. For example, if one of the queues in a set of
2968	* merged queues has a higher weight than a normal queue, then
2969	* the shared queue may inherit such a high weight and, by
2970	* staying almost always active, may force BFQ to perform I/O
2971	* plugging most of the time. This evidently makes it harder
2972	* for BFQ to let the device reach a high throughput.
2973	*
2974	* Finally, the likely() macro below is not used because one
2975	* of the two branches is more likely than the other, but to
2976	* have the code path after the following if() executed as
2977	* fast as possible for the case of a non rotational device
2978	* with queueing. We want it because this is the fastest kind
2979	* of device. On the opposite end, the likely() may lengthen
2980	* the execution time of BFQ for the case of slower devices
2981	* (rotational or at least without queueing). But in this case
2982	* the execution time of BFQ matters very little, if not at
2983	* all.
2984	*/
2985	if (likely(bfqd->nonrot_with_queueing))
2986	return NULL;
2987
2988	/*
2989	* Prevent bfqq from being merged if it has been created too
2990	* long ago. The idea is that true cooperating processes, and
2991	* thus their associated bfq_queues, are supposed to be
2992	* created shortly after each other. This is the case, e.g.,
2993	* for KVM/QEMU and dump I/O threads. Basing on this
2994	* assumption, the following filtering greatly reduces the
2995	* probability that two non-cooperating processes, which just
2996	* happen to do close I/O for some short time interval, have
2997	* their queues merged by mistake.
2998	*/
2999	if (bfq_too_late_for_merging(bfqq))
3000	return NULL;
3001
3002	if (!io_struct || unlikely(bfqq == &bfqd->oom_bfqq))
3003	return NULL;
3004
3005	/* If there is only one backlogged queue, don't search. */
3006	if (bfq_tot_busy_queues(bfqd) == 1)
3007	return NULL;
3008
3009	in_service_bfqq = bfqd->in_service_queue;
3010
3011	if (in_service_bfqq && in_service_bfqq != bfqq &&
3012	likely(in_service_bfqq != &bfqd->oom_bfqq) &&
3013	bfq_rq_close_to_sector(io_struct, request,
3014	sector: bfqd->in_serv_last_pos) &&
3015	bfqq->entity.parent == in_service_bfqq->entity.parent &&
3016	bfq_may_be_close_cooperator(bfqq, new_bfqq: in_service_bfqq)) {
3017	new_bfqq = bfq_setup_merge(bfqq, new_bfqq: in_service_bfqq);
3018	if (new_bfqq)
3019	return new_bfqq;
3020	}
3021	/*
3022	* Check whether there is a cooperator among currently scheduled
3023	* queues. The only thing we need is that the bio/request is not
3024	* NULL, as we need it to establish whether a cooperator exists.
3025	*/
3026	new_bfqq = bfq_find_close_cooperator(bfqd, cur_bfqq: bfqq,
3027	sector: bfq_io_struct_pos(io_struct, request));
3028
3029	if (new_bfqq && likely(new_bfqq != &bfqd->oom_bfqq) &&
3030	bfq_may_be_close_cooperator(bfqq, new_bfqq))
3031	return bfq_setup_merge(bfqq, new_bfqq);
3032
3033	return NULL;
3034	}
3035
3036	static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
3037	{
3038	struct bfq_io_cq *bic = bfqq->bic;
3039	unsigned int a_idx = bfqq->actuator_idx;
3040	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[a_idx];
3041
3042	/*
3043	* If !bfqq->bic, the queue is already shared or its requests
3044	* have already been redirected to a shared queue; both idle window
3045	* and weight raising state have already been saved. Do nothing.
3046	*/
3047	if (!bic)
3048	return;
3049
3050	bfqq_data->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
3051	bfqq_data->saved_inject_limit = bfqq->inject_limit;
3052	bfqq_data->saved_decrease_time_jif = bfqq->decrease_time_jif;
3053
3054	bfqq_data->saved_weight = bfqq->entity.orig_weight;
3055	bfqq_data->saved_ttime = bfqq->ttime;
3056	bfqq_data->saved_has_short_ttime =
3057	bfq_bfqq_has_short_ttime(bfqq);
3058	bfqq_data->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
3059	bfqq_data->saved_io_start_time = bfqq->io_start_time;
3060	bfqq_data->saved_tot_idle_time = bfqq->tot_idle_time;
3061	bfqq_data->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
3062	bfqq_data->was_in_burst_list =
3063	!hlist_unhashed(h: &bfqq->burst_list_node);
3064
3065	if (unlikely(bfq_bfqq_just_created(bfqq) &&
3066	!bfq_bfqq_in_large_burst(bfqq) &&
3067	bfqq->bfqd->low_latency)) {
3068	/*
3069	* bfqq being merged right after being created: bfqq
3070	* would have deserved interactive weight raising, but
3071	* did not make it to be set in a weight-raised state,
3072	* because of this early merge. Store directly the
3073	* weight-raising state that would have been assigned
3074	* to bfqq, so that to avoid that bfqq unjustly fails
3075	* to enjoy weight raising if split soon.
3076	*/
3077	bfqq_data->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
3078	bfqq_data->saved_wr_start_at_switch_to_srt =
3079	bfq_smallest_from_now();
3080	bfqq_data->saved_wr_cur_max_time =
3081	bfq_wr_duration(bfqd: bfqq->bfqd);
3082	bfqq_data->saved_last_wr_start_finish = jiffies;
3083	} else {
3084	bfqq_data->saved_wr_coeff = bfqq->wr_coeff;
3085	bfqq_data->saved_wr_start_at_switch_to_srt =
3086	bfqq->wr_start_at_switch_to_srt;
3087	bfqq_data->saved_service_from_wr =
3088	bfqq->service_from_wr;
3089	bfqq_data->saved_last_wr_start_finish =
3090	bfqq->last_wr_start_finish;
3091	bfqq_data->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
3092	}
3093	}
3094
3095
3096	static void
3097	bfq_reassign_last_bfqq(struct bfq_queue *cur_bfqq, struct bfq_queue *new_bfqq)
3098	{
3099	if (cur_bfqq->entity.parent &&
3100	cur_bfqq->entity.parent->last_bfqq_created == cur_bfqq)
3101	cur_bfqq->entity.parent->last_bfqq_created = new_bfqq;
3102	else if (cur_bfqq->bfqd && cur_bfqq->bfqd->last_bfqq_created == cur_bfqq)
3103	cur_bfqq->bfqd->last_bfqq_created = new_bfqq;
3104	}
3105
3106	void bfq_release_process_ref(struct bfq_data *bfqd, struct bfq_queue *bfqq)
3107	{
3108	/*
3109	* To prevent bfqq's service guarantees from being violated,
3110	* bfqq may be left busy, i.e., queued for service, even if
3111	* empty (see comments in __bfq_bfqq_expire() for
3112	* details). But, if no process will send requests to bfqq any
3113	* longer, then there is no point in keeping bfqq queued for
3114	* service. In addition, keeping bfqq queued for service, but
3115	* with no process ref any longer, may have caused bfqq to be
3116	* freed when dequeued from service. But this is assumed to
3117	* never happen.
3118	*/
3119	if (bfq_bfqq_busy(bfqq) && RB_EMPTY_ROOT(&bfqq->sort_list) &&
3120	bfqq != bfqd->in_service_queue)
3121	bfq_del_bfqq_busy(bfqq, expiration: false);
3122
3123	bfq_reassign_last_bfqq(cur_bfqq: bfqq, NULL);
3124
3125	bfq_put_queue(bfqq);
3126	}
3127
3128	static void
3129	bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
3130	struct bfq_queue *bfqq, struct bfq_queue *new_bfqq)
3131	{
3132	bfq_log_bfqq(bfqd, bfqq, "merging with queue %lu",
3133	(unsigned long)new_bfqq->pid);
3134	/* Save weight raising and idle window of the merged queues */
3135	bfq_bfqq_save_state(bfqq);
3136	bfq_bfqq_save_state(bfqq: new_bfqq);
3137	if (bfq_bfqq_IO_bound(bfqq))
3138	bfq_mark_bfqq_IO_bound(bfqq: new_bfqq);
3139	bfq_clear_bfqq_IO_bound(bfqq);
3140
3141	/*
3142	* The processes associated with bfqq are cooperators of the
3143	* processes associated with new_bfqq. So, if bfqq has a
3144	* waker, then assume that all these processes will be happy
3145	* to let bfqq's waker freely inject I/O when they have no
3146	* I/O.
3147	*/
3148	if (bfqq->waker_bfqq && !new_bfqq->waker_bfqq &&
3149	bfqq->waker_bfqq != new_bfqq) {
3150	new_bfqq->waker_bfqq = bfqq->waker_bfqq;
3151	new_bfqq->tentative_waker_bfqq = NULL;
3152
3153	/*
3154	* If the waker queue disappears, then
3155	* new_bfqq->waker_bfqq must be reset. So insert
3156	* new_bfqq into the woken_list of the waker. See
3157	* bfq_check_waker for details.
3158	*/
3159	hlist_add_head(n: &new_bfqq->woken_list_node,
3160	h: &new_bfqq->waker_bfqq->woken_list);
3161
3162	}
3163
3164	/*
3165	* If bfqq is weight-raised, then let new_bfqq inherit
3166	* weight-raising. To reduce false positives, neglect the case
3167	* where bfqq has just been created, but has not yet made it
3168	* to be weight-raised (which may happen because EQM may merge
3169	* bfqq even before bfq_add_request is executed for the first
3170	* time for bfqq). Handling this case would however be very
3171	* easy, thanks to the flag just_created.
3172	*/
3173	if (new_bfqq->wr_coeff == 1 && bfqq->wr_coeff > 1) {
3174	new_bfqq->wr_coeff = bfqq->wr_coeff;
3175	new_bfqq->wr_cur_max_time = bfqq->wr_cur_max_time;
3176	new_bfqq->last_wr_start_finish = bfqq->last_wr_start_finish;
3177	new_bfqq->wr_start_at_switch_to_srt =
3178	bfqq->wr_start_at_switch_to_srt;
3179	if (bfq_bfqq_busy(bfqq: new_bfqq))
3180	bfqd->wr_busy_queues++;
3181	new_bfqq->entity.prio_changed = 1;
3182	}
3183
3184	if (bfqq->wr_coeff > 1) { /* bfqq has given its wr to new_bfqq */
3185	bfqq->wr_coeff = 1;
3186	bfqq->entity.prio_changed = 1;
3187	if (bfq_bfqq_busy(bfqq))
3188	bfqd->wr_busy_queues--;
3189	}
3190
3191	bfq_log_bfqq(bfqd, new_bfqq, "merge_bfqqs: wr_busy %d",
3192	bfqd->wr_busy_queues);
3193
3194	/*
3195	* Merge queues (that is, let bic redirect its requests to new_bfqq)
3196	*/
3197	bic_set_bfqq(bic, bfqq: new_bfqq, is_sync: true, actuator_idx: bfqq->actuator_idx);
3198	bfq_mark_bfqq_coop(bfqq: new_bfqq);
3199	/*
3200	* new_bfqq now belongs to at least two bics (it is a shared queue):
3201	* set new_bfqq->bic to NULL. bfqq either:
3202	* - does not belong to any bic any more, and hence bfqq->bic must
3203	* be set to NULL, or
3204	* - is a queue whose owning bics have already been redirected to a
3205	* different queue, hence the queue is destined to not belong to
3206	* any bic soon and bfqq->bic is already NULL (therefore the next
3207	* assignment causes no harm).
3208	*/
3209	new_bfqq->bic = NULL;
3210	/*
3211	* If the queue is shared, the pid is the pid of one of the associated
3212	* processes. Which pid depends on the exact sequence of merge events
3213	* the queue underwent. So printing such a pid is useless and confusing
3214	* because it reports a random pid between those of the associated
3215	* processes.
3216	* We mark such a queue with a pid -1, and then print SHARED instead of
3217	* a pid in logging messages.
3218	*/
3219	new_bfqq->pid = -1;
3220	bfqq->bic = NULL;
3221
3222	bfq_reassign_last_bfqq(cur_bfqq: bfqq, new_bfqq);
3223
3224	bfq_release_process_ref(bfqd, bfqq);
3225	}
3226
3227	static bool bfq_allow_bio_merge(struct request_queue *q, struct request *rq,
3228	struct bio *bio)
3229	{
3230	struct bfq_data *bfqd = q->elevator->elevator_data;
3231	bool is_sync = op_is_sync(op: bio->bi_opf);
3232	struct bfq_queue *bfqq = bfqd->bio_bfqq, *new_bfqq;
3233
3234	/*
3235	* Disallow merge of a sync bio into an async request.
3236	*/
3237	if (is_sync && !rq_is_sync(rq))
3238	return false;
3239
3240	/*
3241	* Lookup the bfqq that this bio will be queued with. Allow
3242	* merge only if rq is queued there.
3243	*/
3244	if (!bfqq)
3245	return false;
3246
3247	/*
3248	* We take advantage of this function to perform an early merge
3249	* of the queues of possible cooperating processes.
3250	*/
3251	new_bfqq = bfq_setup_cooperator(bfqd, bfqq, io_struct: bio, request: false, bic: bfqd->bio_bic);
3252	if (new_bfqq) {
3253	/*
3254	* bic still points to bfqq, then it has not yet been
3255	* redirected to some other bfq_queue, and a queue
3256	* merge between bfqq and new_bfqq can be safely
3257	* fulfilled, i.e., bic can be redirected to new_bfqq
3258	* and bfqq can be put.
3259	*/
3260	bfq_merge_bfqqs(bfqd, bic: bfqd->bio_bic, bfqq,
3261	new_bfqq);
3262	/*
3263	* If we get here, bio will be queued into new_queue,
3264	* so use new_bfqq to decide whether bio and rq can be
3265	* merged.
3266	*/
3267	bfqq = new_bfqq;
3268
3269	/*
3270	* Change also bqfd->bio_bfqq, as
3271	* bfqd->bio_bic now points to new_bfqq, and
3272	* this function may be invoked again (and then may
3273	* use again bqfd->bio_bfqq).
3274	*/
3275	bfqd->bio_bfqq = bfqq;
3276	}
3277
3278	return bfqq == RQ_BFQQ(rq);
3279	}
3280
3281	/*
3282	* Set the maximum time for the in-service queue to consume its
3283	* budget. This prevents seeky processes from lowering the throughput.
3284	* In practice, a time-slice service scheme is used with seeky
3285	* processes.
3286	*/
3287	static void bfq_set_budget_timeout(struct bfq_data *bfqd,
3288	struct bfq_queue *bfqq)
3289	{
3290	unsigned int timeout_coeff;
3291
3292	if (bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time)
3293	timeout_coeff = 1;
3294	else
3295	timeout_coeff = bfqq->entity.weight / bfqq->entity.orig_weight;
3296
3297	bfqd->last_budget_start = blk_time_get();
3298
3299	bfqq->budget_timeout = jiffies +
3300	bfqd->bfq_timeout * timeout_coeff;
3301	}
3302
3303	static void __bfq_set_in_service_queue(struct bfq_data *bfqd,
3304	struct bfq_queue *bfqq)
3305	{
3306	if (bfqq) {
3307	bfq_clear_bfqq_fifo_expire(bfqq);
3308
3309	bfqd->budgets_assigned = (bfqd->budgets_assigned * 7 + 256) / 8;
3310
3311	if (time_is_before_jiffies(bfqq->last_wr_start_finish) &&
3312	bfqq->wr_coeff > 1 &&
3313	bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
3314	time_is_before_jiffies(bfqq->budget_timeout)) {
3315	/*
3316	* For soft real-time queues, move the start
3317	* of the weight-raising period forward by the
3318	* time the queue has not received any
3319	* service. Otherwise, a relatively long
3320	* service delay is likely to cause the
3321	* weight-raising period of the queue to end,
3322	* because of the short duration of the
3323	* weight-raising period of a soft real-time
3324	* queue. It is worth noting that this move
3325	* is not so dangerous for the other queues,
3326	* because soft real-time queues are not
3327	* greedy.
3328	*
3329	* To not add a further variable, we use the
3330	* overloaded field budget_timeout to
3331	* determine for how long the queue has not
3332	* received service, i.e., how much time has
3333	* elapsed since the queue expired. However,
3334	* this is a little imprecise, because
3335	* budget_timeout is set to jiffies if bfqq
3336	* not only expires, but also remains with no
3337	* request.
3338	*/
3339	if (time_after(bfqq->budget_timeout,
3340	bfqq->last_wr_start_finish))
3341	bfqq->last_wr_start_finish +=
3342	jiffies - bfqq->budget_timeout;
3343	else
3344	bfqq->last_wr_start_finish = jiffies;
3345	}
3346
3347	bfq_set_budget_timeout(bfqd, bfqq);
3348	bfq_log_bfqq(bfqd, bfqq,
3349	"set_in_service_queue, cur-budget = %d",
3350	bfqq->entity.budget);
3351	}
3352
3353	bfqd->in_service_queue = bfqq;
3354	bfqd->in_serv_last_pos = 0;
3355	}
3356
3357	/*
3358	* Get and set a new queue for service.
3359	*/
3360	static struct bfq_queue *bfq_set_in_service_queue(struct bfq_data *bfqd)
3361	{
3362	struct bfq_queue *bfqq = bfq_get_next_queue(bfqd);
3363
3364	__bfq_set_in_service_queue(bfqd, bfqq);
3365	return bfqq;
3366	}
3367
3368	static void bfq_arm_slice_timer(struct bfq_data *bfqd)
3369	{
3370	struct bfq_queue *bfqq = bfqd->in_service_queue;
3371	u32 sl;
3372
3373	bfq_mark_bfqq_wait_request(bfqq);
3374
3375	/*
3376	* We don't want to idle for seeks, but we do want to allow
3377	* fair distribution of slice time for a process doing back-to-back
3378	* seeks. So allow a little bit of time for him to submit a new rq.
3379	*/
3380	sl = bfqd->bfq_slice_idle;
3381	/*
3382	* Unless the queue is being weight-raised or the scenario is
3383	* asymmetric, grant only minimum idle time if the queue
3384	* is seeky. A long idling is preserved for a weight-raised
3385	* queue, or, more in general, in an asymmetric scenario,
3386	* because a long idling is needed for guaranteeing to a queue
3387	* its reserved share of the throughput (in particular, it is
3388	* needed if the queue has a higher weight than some other
3389	* queue).
3390	*/
3391	if (BFQQ_SEEKY(bfqq) && bfqq->wr_coeff == 1 &&
3392	!bfq_asymmetric_scenario(bfqd, bfqq))
3393	sl = min_t(u64, sl, BFQ_MIN_TT);
3394	else if (bfqq->wr_coeff > 1)
3395	sl = max_t(u32, sl, 20ULL * NSEC_PER_MSEC);
3396
3397	bfqd->last_idling_start = blk_time_get();
3398	bfqd->last_idling_start_jiffies = jiffies;
3399
3400	hrtimer_start(timer: &bfqd->idle_slice_timer, tim: ns_to_ktime(ns: sl),
3401	mode: HRTIMER_MODE_REL);
3402	bfqg_stats_set_start_idle_time(bfqg: bfqq_group(bfqq));
3403	}
3404
3405	/*
3406	* In autotuning mode, max_budget is dynamically recomputed as the
3407	* amount of sectors transferred in timeout at the estimated peak
3408	* rate. This enables BFQ to utilize a full timeslice with a full
3409	* budget, even if the in-service queue is served at peak rate. And
3410	* this maximises throughput with sequential workloads.
3411	*/
3412	static unsigned long bfq_calc_max_budget(struct bfq_data *bfqd)
3413	{
3414	return (u64)bfqd->peak_rate * USEC_PER_MSEC *
3415	jiffies_to_msecs(j: bfqd->bfq_timeout)>>BFQ_RATE_SHIFT;
3416	}
3417
3418	/*
3419	* Update parameters related to throughput and responsiveness, as a
3420	* function of the estimated peak rate. See comments on
3421	* bfq_calc_max_budget(), and on the ref_wr_duration array.
3422	*/
3423	static void update_thr_responsiveness_params(struct bfq_data *bfqd)
3424	{
3425	if (bfqd->bfq_user_max_budget == 0) {
3426	bfqd->bfq_max_budget =
3427	bfq_calc_max_budget(bfqd);
3428	bfq_log(bfqd, "new max_budget = %d", bfqd->bfq_max_budget);
3429	}
3430	}
3431
3432	static void bfq_reset_rate_computation(struct bfq_data *bfqd,
3433	struct request *rq)
3434	{
3435	if (rq != NULL) { /* new rq dispatch now, reset accordingly */
3436	bfqd->last_dispatch = bfqd->first_dispatch = blk_time_get_ns();
3437	bfqd->peak_rate_samples = 1;
3438	bfqd->sequential_samples = 0;
3439	bfqd->tot_sectors_dispatched = bfqd->last_rq_max_size =
3440	blk_rq_sectors(rq);
3441	} else /* no new rq dispatched, just reset the number of samples */
3442	bfqd->peak_rate_samples = 0; /* full re-init on next disp. */
3443
3444	bfq_log(bfqd,
3445	"reset_rate_computation at end, sample %u/%u tot_sects %llu",
3446	bfqd->peak_rate_samples, bfqd->sequential_samples,
3447	bfqd->tot_sectors_dispatched);
3448	}
3449
3450	static void bfq_update_rate_reset(struct bfq_data *bfqd, struct request *rq)
3451	{
3452	u32 rate, weight, divisor;
3453
3454	/*
3455	* For the convergence property to hold (see comments on
3456	* bfq_update_peak_rate()) and for the assessment to be
3457	* reliable, a minimum number of samples must be present, and
3458	* a minimum amount of time must have elapsed. If not so, do
3459	* not compute new rate. Just reset parameters, to get ready
3460	* for a new evaluation attempt.
3461	*/
3462	if (bfqd->peak_rate_samples < BFQ_RATE_MIN_SAMPLES ||
3463	bfqd->delta_from_first < BFQ_RATE_MIN_INTERVAL)
3464	goto reset_computation;
3465
3466	/*
3467	* If a new request completion has occurred after last
3468	* dispatch, then, to approximate the rate at which requests
3469	* have been served by the device, it is more precise to
3470	* extend the observation interval to the last completion.
3471	*/
3472	bfqd->delta_from_first =
3473	max_t(u64, bfqd->delta_from_first,
3474	bfqd->last_completion - bfqd->first_dispatch);
3475
3476	/*
3477	* Rate computed in sects/usec, and not sects/nsec, for
3478	* precision issues.
3479	*/
3480	rate = div64_ul(bfqd->tot_sectors_dispatched<<BFQ_RATE_SHIFT,
3481	div_u64(bfqd->delta_from_first, NSEC_PER_USEC));
3482
3483	/*
3484	* Peak rate not updated if:
3485	* - the percentage of sequential dispatches is below 3/4 of the
3486	* total, and rate is below the current estimated peak rate
3487	* - rate is unreasonably high (> 20M sectors/sec)
3488	*/
3489	if ((bfqd->sequential_samples < (3 * bfqd->peak_rate_samples)>>2 &&
3490	rate <= bfqd->peak_rate) ||
3491	rate > 20<<BFQ_RATE_SHIFT)
3492	goto reset_computation;
3493
3494	/*
3495	* We have to update the peak rate, at last! To this purpose,
3496	* we use a low-pass filter. We compute the smoothing constant
3497	* of the filter as a function of the 'weight' of the new
3498	* measured rate.
3499	*
3500	* As can be seen in next formulas, we define this weight as a
3501	* quantity proportional to how sequential the workload is,
3502	* and to how long the observation time interval is.
3503	*
3504	* The weight runs from 0 to 8. The maximum value of the
3505	* weight, 8, yields the minimum value for the smoothing
3506	* constant. At this minimum value for the smoothing constant,
3507	* the measured rate contributes for half of the next value of
3508	* the estimated peak rate.
3509	*
3510	* So, the first step is to compute the weight as a function
3511	* of how sequential the workload is. Note that the weight
3512	* cannot reach 9, because bfqd->sequential_samples cannot
3513	* become equal to bfqd->peak_rate_samples, which, in its
3514	* turn, holds true because bfqd->sequential_samples is not
3515	* incremented for the first sample.
3516	*/
3517	weight = (9 * bfqd->sequential_samples) / bfqd->peak_rate_samples;
3518
3519	/*
3520	* Second step: further refine the weight as a function of the
3521	* duration of the observation interval.
3522	*/
3523	weight = min_t(u32, 8,
3524	div_u64(weight * bfqd->delta_from_first,
3525	BFQ_RATE_REF_INTERVAL));
3526
3527	/*
3528	* Divisor ranging from 10, for minimum weight, to 2, for
3529	* maximum weight.
3530	*/
3531	divisor = 10 - weight;
3532
3533	/*
3534	* Finally, update peak rate:
3535	*
3536	* peak_rate = peak_rate * (divisor-1) / divisor + rate / divisor
3537	*/
3538	bfqd->peak_rate *= divisor-1;
3539	bfqd->peak_rate /= divisor;
3540	rate /= divisor; /* smoothing constant alpha = 1/divisor */
3541
3542	bfqd->peak_rate += rate;
3543
3544	/*
3545	* For a very slow device, bfqd->peak_rate can reach 0 (see
3546	* the minimum representable values reported in the comments
3547	* on BFQ_RATE_SHIFT). Push to 1 if this happens, to avoid
3548	* divisions by zero where bfqd->peak_rate is used as a
3549	* divisor.
3550	*/
3551	bfqd->peak_rate = max_t(u32, 1, bfqd->peak_rate);
3552
3553	update_thr_responsiveness_params(bfqd);
3554
3555	reset_computation:
3556	bfq_reset_rate_computation(bfqd, rq);
3557	}
3558
3559	/*
3560	* Update the read/write peak rate (the main quantity used for
3561	* auto-tuning, see update_thr_responsiveness_params()).
3562	*
3563	* It is not trivial to estimate the peak rate (correctly): because of
3564	* the presence of sw and hw queues between the scheduler and the
3565	* device components that finally serve I/O requests, it is hard to
3566	* say exactly when a given dispatched request is served inside the
3567	* device, and for how long. As a consequence, it is hard to know
3568	* precisely at what rate a given set of requests is actually served
3569	* by the device.
3570	*
3571	* On the opposite end, the dispatch time of any request is trivially
3572	* available, and, from this piece of information, the "dispatch rate"
3573	* of requests can be immediately computed. So, the idea in the next
3574	* function is to use what is known, namely request dispatch times
3575	* (plus, when useful, request completion times), to estimate what is
3576	* unknown, namely in-device request service rate.
3577	*
3578	* The main issue is that, because of the above facts, the rate at
3579	* which a certain set of requests is dispatched over a certain time
3580	* interval can vary greatly with respect to the rate at which the
3581	* same requests are then served. But, since the size of any
3582	* intermediate queue is limited, and the service scheme is lossless
3583	* (no request is silently dropped), the following obvious convergence
3584	* property holds: the number of requests dispatched MUST become
3585	* closer and closer to the number of requests completed as the
3586	* observation interval grows. This is the key property used in
3587	* the next function to estimate the peak service rate as a function
3588	* of the observed dispatch rate. The function assumes to be invoked
3589	* on every request dispatch.
3590	*/
3591	static void bfq_update_peak_rate(struct bfq_data *bfqd, struct request *rq)
3592	{
3593	u64 now_ns = blk_time_get_ns();
3594
3595	if (bfqd->peak_rate_samples == 0) { /* first dispatch */
3596	bfq_log(bfqd, "update_peak_rate: goto reset, samples %d",
3597	bfqd->peak_rate_samples);
3598	bfq_reset_rate_computation(bfqd, rq);
3599	goto update_last_values; /* will add one sample */
3600	}
3601
3602	/*
3603	* Device idle for very long: the observation interval lasting
3604	* up to this dispatch cannot be a valid observation interval
3605	* for computing a new peak rate (similarly to the late-
3606	* completion event in bfq_completed_request()). Go to
3607	* update_rate_and_reset to have the following three steps
3608	* taken:
3609	* - close the observation interval at the last (previous)
3610	* request dispatch or completion
3611	* - compute rate, if possible, for that observation interval
3612	* - start a new observation interval with this dispatch
3613	*/
3614	if (now_ns - bfqd->last_dispatch > 100*NSEC_PER_MSEC &&
3615	bfqd->tot_rq_in_driver == 0)
3616	goto update_rate_and_reset;
3617
3618	/* Update sampling information */
3619	bfqd->peak_rate_samples++;
3620
3621	if ((bfqd->tot_rq_in_driver > 0 ||
3622	now_ns - bfqd->last_completion < BFQ_MIN_TT)
3623	&& !BFQ_RQ_SEEKY(bfqd, bfqd->last_position, rq))
3624	bfqd->sequential_samples++;
3625
3626	bfqd->tot_sectors_dispatched += blk_rq_sectors(rq);
3627
3628	/* Reset max observed rq size every 32 dispatches */
3629	if (likely(bfqd->peak_rate_samples % 32))
3630	bfqd->last_rq_max_size =
3631	max_t(u32, blk_rq_sectors(rq), bfqd->last_rq_max_size);
3632	else
3633	bfqd->last_rq_max_size = blk_rq_sectors(rq);
3634
3635	bfqd->delta_from_first = now_ns - bfqd->first_dispatch;
3636
3637	/* Target observation interval not yet reached, go on sampling */
3638	if (bfqd->delta_from_first < BFQ_RATE_REF_INTERVAL)
3639	goto update_last_values;
3640
3641	update_rate_and_reset:
3642	bfq_update_rate_reset(bfqd, rq);
3643	update_last_values:
3644	bfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
3645	if (RQ_BFQQ(rq) == bfqd->in_service_queue)
3646	bfqd->in_serv_last_pos = bfqd->last_position;
3647	bfqd->last_dispatch = now_ns;
3648	}
3649
3650	/*
3651	* Remove request from internal lists.
3652	*/
3653	static void bfq_dispatch_remove(struct request_queue *q, struct request *rq)
3654	{
3655	struct bfq_queue *bfqq = RQ_BFQQ(rq);
3656
3657	/*
3658	* For consistency, the next instruction should have been
3659	* executed after removing the request from the queue and
3660	* dispatching it. We execute instead this instruction before
3661	* bfq_remove_request() (and hence introduce a temporary
3662	* inconsistency), for efficiency. In fact, should this
3663	* dispatch occur for a non in-service bfqq, this anticipated
3664	* increment prevents two counters related to bfqq->dispatched
3665	* from risking to be, first, uselessly decremented, and then
3666	* incremented again when the (new) value of bfqq->dispatched
3667	* happens to be taken into account.
3668	*/
3669	bfqq->dispatched++;
3670	bfq_update_peak_rate(bfqd: q->elevator->elevator_data, rq);
3671
3672	bfq_remove_request(q, rq);
3673	}
3674
3675	/*
3676	* There is a case where idling does not have to be performed for
3677	* throughput concerns, but to preserve the throughput share of
3678	* the process associated with bfqq.
3679	*
3680	* To introduce this case, we can note that allowing the drive
3681	* to enqueue more than one request at a time, and hence
3682	* delegating de facto final scheduling decisions to the
3683	* drive's internal scheduler, entails loss of control on the
3684	* actual request service order. In particular, the critical
3685	* situation is when requests from different processes happen
3686	* to be present, at the same time, in the internal queue(s)
3687	* of the drive. In such a situation, the drive, by deciding
3688	* the service order of the internally-queued requests, does
3689	* determine also the actual throughput distribution among
3690	* these processes. But the drive typically has no notion or
3691	* concern about per-process throughput distribution, and
3692	* makes its decisions only on a per-request basis. Therefore,
3693	* the service distribution enforced by the drive's internal
3694	* scheduler is likely to coincide with the desired throughput
3695	* distribution only in a completely symmetric, or favorably
3696	* skewed scenario where:
3697	* (i-a) each of these processes must get the same throughput as
3698	* the others,
3699	* (i-b) in case (i-a) does not hold, it holds that the process
3700	* associated with bfqq must receive a lower or equal
3701	* throughput than any of the other processes;
3702	* (ii) the I/O of each process has the same properties, in
3703	* terms of locality (sequential or random), direction
3704	* (reads or writes), request sizes, greediness
3705	* (from I/O-bound to sporadic), and so on;
3706
3707	* In fact, in such a scenario, the drive tends to treat the requests
3708	* of each process in about the same way as the requests of the
3709	* others, and thus to provide each of these processes with about the
3710	* same throughput. This is exactly the desired throughput
3711	* distribution if (i-a) holds, or, if (i-b) holds instead, this is an
3712	* even more convenient distribution for (the process associated with)
3713	* bfqq.
3714	*
3715	* In contrast, in any asymmetric or unfavorable scenario, device
3716	* idling (I/O-dispatch plugging) is certainly needed to guarantee
3717	* that bfqq receives its assigned fraction of the device throughput
3718	* (see [1] for details).
3719	*
3720	* The problem is that idling may significantly reduce throughput with
3721	* certain combinations of types of I/O and devices. An important
3722	* example is sync random I/O on flash storage with command
3723	* queueing. So, unless bfqq falls in cases where idling also boosts
3724	* throughput, it is important to check conditions (i-a), i(-b) and
3725	* (ii) accurately, so as to avoid idling when not strictly needed for
3726	* service guarantees.
3727	*
3728	* Unfortunately, it is extremely difficult to thoroughly check
3729	* condition (ii). And, in case there are active groups, it becomes
3730	* very difficult to check conditions (i-a) and (i-b) too. In fact,
3731	* if there are active groups, then, for conditions (i-a) or (i-b) to
3732	* become false 'indirectly', it is enough that an active group
3733	* contains more active processes or sub-groups than some other active
3734	* group. More precisely, for conditions (i-a) or (i-b) to become
3735	* false because of such a group, it is not even necessary that the
3736	* group is (still) active: it is sufficient that, even if the group
3737	* has become inactive, some of its descendant processes still have
3738	* some request already dispatched but still waiting for
3739	* completion. In fact, requests have still to be guaranteed their
3740	* share of the throughput even after being dispatched. In this
3741	* respect, it is easy to show that, if a group frequently becomes
3742	* inactive while still having in-flight requests, and if, when this
3743	* happens, the group is not considered in the calculation of whether
3744	* the scenario is asymmetric, then the group may fail to be
3745	* guaranteed its fair share of the throughput (basically because
3746	* idling may not be performed for the descendant processes of the
3747	* group, but it had to be). We address this issue with the following
3748	* bi-modal behavior, implemented in the function
3749	* bfq_asymmetric_scenario().
3750	*
3751	* If there are groups with requests waiting for completion
3752	* (as commented above, some of these groups may even be
3753	* already inactive), then the scenario is tagged as
3754	* asymmetric, conservatively, without checking any of the
3755	* conditions (i-a), (i-b) or (ii). So the device is idled for bfqq.
3756	* This behavior matches also the fact that groups are created
3757	* exactly if controlling I/O is a primary concern (to
3758	* preserve bandwidth and latency guarantees).
3759	*
3760	* On the opposite end, if there are no groups with requests waiting
3761	* for completion, then only conditions (i-a) and (i-b) are actually
3762	* controlled, i.e., provided that conditions (i-a) or (i-b) holds,
3763	* idling is not performed, regardless of whether condition (ii)
3764	* holds. In other words, only if conditions (i-a) and (i-b) do not
3765	* hold, then idling is allowed, and the device tends to be prevented
3766	* from queueing many requests, possibly of several processes. Since
3767	* there are no groups with requests waiting for completion, then, to
3768	* control conditions (i-a) and (i-b) it is enough to check just
3769	* whether all the queues with requests waiting for completion also
3770	* have the same weight.
3771	*
3772	* Not checking condition (ii) evidently exposes bfqq to the
3773	* risk of getting less throughput than its fair share.
3774	* However, for queues with the same weight, a further
3775	* mechanism, preemption, mitigates or even eliminates this
3776	* problem. And it does so without consequences on overall
3777	* throughput. This mechanism and its benefits are explained
3778	* in the next three paragraphs.
3779	*
3780	* Even if a queue, say Q, is expired when it remains idle, Q
3781	* can still preempt the new in-service queue if the next
3782	* request of Q arrives soon (see the comments on
3783	* bfq_bfqq_update_budg_for_activation). If all queues and
3784	* groups have the same weight, this form of preemption,
3785	* combined with the hole-recovery heuristic described in the
3786	* comments on function bfq_bfqq_update_budg_for_activation,
3787	* are enough to preserve a correct bandwidth distribution in
3788	* the mid term, even without idling. In fact, even if not
3789	* idling allows the internal queues of the device to contain
3790	* many requests, and thus to reorder requests, we can rather
3791	* safely assume that the internal scheduler still preserves a
3792	* minimum of mid-term fairness.
3793	*
3794	* More precisely, this preemption-based, idleless approach
3795	* provides fairness in terms of IOPS, and not sectors per
3796	* second. This can be seen with a simple example. Suppose
3797	* that there are two queues with the same weight, but that
3798	* the first queue receives requests of 8 sectors, while the
3799	* second queue receives requests of 1024 sectors. In
3800	* addition, suppose that each of the two queues contains at
3801	* most one request at a time, which implies that each queue
3802	* always remains idle after it is served. Finally, after
3803	* remaining idle, each queue receives very quickly a new
3804	* request. It follows that the two queues are served
3805	* alternatively, preempting each other if needed. This
3806	* implies that, although both queues have the same weight,
3807	* the queue with large requests receives a service that is
3808	* 1024/8 times as high as the service received by the other
3809	* queue.
3810	*
3811	* The motivation for using preemption instead of idling (for
3812	* queues with the same weight) is that, by not idling,
3813	* service guarantees are preserved (completely or at least in
3814	* part) without minimally sacrificing throughput. And, if
3815	* there is no active group, then the primary expectation for
3816	* this device is probably a high throughput.
3817	*
3818	* We are now left only with explaining the two sub-conditions in the
3819	* additional compound condition that is checked below for deciding
3820	* whether the scenario is asymmetric. To explain the first
3821	* sub-condition, we need to add that the function
3822	* bfq_asymmetric_scenario checks the weights of only
3823	* non-weight-raised queues, for efficiency reasons (see comments on
3824	* bfq_weights_tree_add()). Then the fact that bfqq is weight-raised
3825	* is checked explicitly here. More precisely, the compound condition
3826	* below takes into account also the fact that, even if bfqq is being
3827	* weight-raised, the scenario is still symmetric if all queues with
3828	* requests waiting for completion happen to be
3829	* weight-raised. Actually, we should be even more precise here, and
3830	* differentiate between interactive weight raising and soft real-time
3831	* weight raising.
3832	*
3833	* The second sub-condition checked in the compound condition is
3834	* whether there is a fair amount of already in-flight I/O not
3835	* belonging to bfqq. If so, I/O dispatching is to be plugged, for the
3836	* following reason. The drive may decide to serve in-flight
3837	* non-bfqq's I/O requests before bfqq's ones, thereby delaying the
3838	* arrival of new I/O requests for bfqq (recall that bfqq is sync). If
3839	* I/O-dispatching is not plugged, then, while bfqq remains empty, a
3840	* basically uncontrolled amount of I/O from other queues may be
3841	* dispatched too, possibly causing the service of bfqq's I/O to be
3842	* delayed even longer in the drive. This problem gets more and more
3843	* serious as the speed and the queue depth of the drive grow,
3844	* because, as these two quantities grow, the probability to find no
3845	* queue busy but many requests in flight grows too. By contrast,
3846	* plugging I/O dispatching minimizes the delay induced by already
3847	* in-flight I/O, and enables bfqq to recover the bandwidth it may
3848	* lose because of this delay.
3849	*
3850	* As a side note, it is worth considering that the above
3851	* device-idling countermeasures may however fail in the following
3852	* unlucky scenario: if I/O-dispatch plugging is (correctly) disabled
3853	* in a time period during which all symmetry sub-conditions hold, and
3854	* therefore the device is allowed to enqueue many requests, but at
3855	* some later point in time some sub-condition stops to hold, then it
3856	* may become impossible to make requests be served in the desired
3857	* order until all the requests already queued in the device have been
3858	* served. The last sub-condition commented above somewhat mitigates
3859	* this problem for weight-raised queues.
3860	*
3861	* However, as an additional mitigation for this problem, we preserve
3862	* plugging for a special symmetric case that may suddenly turn into
3863	* asymmetric: the case where only bfqq is busy. In this case, not
3864	* expiring bfqq does not cause any harm to any other queues in terms
3865	* of service guarantees. In contrast, it avoids the following unlucky
3866	* sequence of events: (1) bfqq is expired, (2) a new queue with a
3867	* lower weight than bfqq becomes busy (or more queues), (3) the new
3868	* queue is served until a new request arrives for bfqq, (4) when bfqq
3869	* is finally served, there are so many requests of the new queue in
3870	* the drive that the pending requests for bfqq take a lot of time to
3871	* be served. In particular, event (2) may case even already
3872	* dispatched requests of bfqq to be delayed, inside the drive. So, to
3873	* avoid this series of events, the scenario is preventively declared
3874	* as asymmetric also if bfqq is the only busy queues
3875	*/
3876	static bool idling_needed_for_service_guarantees(struct bfq_data *bfqd,
3877	struct bfq_queue *bfqq)
3878	{
3879	int tot_busy_queues = bfq_tot_busy_queues(bfqd);
3880
3881	/* No point in idling for bfqq if it won't get requests any longer */
3882	if (unlikely(!bfqq_process_refs(bfqq)))
3883	return false;
3884
3885	return (bfqq->wr_coeff > 1 &&
3886	(bfqd->wr_busy_queues < tot_busy_queues ||
3887	bfqd->tot_rq_in_driver >= bfqq->dispatched + 4)) ||
3888	bfq_asymmetric_scenario(bfqd, bfqq) ||
3889	tot_busy_queues == 1;
3890	}
3891
3892	static bool __bfq_bfqq_expire(struct bfq_data *bfqd, struct bfq_queue *bfqq,
3893	enum bfqq_expiration reason)
3894	{
3895	/*
3896	* If this bfqq is shared between multiple processes, check
3897	* to make sure that those processes are still issuing I/Os
3898	* within the mean seek distance. If not, it may be time to
3899	* break the queues apart again.
3900	*/
3901	if (bfq_bfqq_coop(bfqq) && BFQQ_SEEKY(bfqq))
3902	bfq_mark_bfqq_split_coop(bfqq);
3903
3904	/*
3905	* Consider queues with a higher finish virtual time than
3906	* bfqq. If idling_needed_for_service_guarantees(bfqq) returns
3907	* true, then bfqq's bandwidth would be violated if an
3908	* uncontrolled amount of I/O from these queues were
3909	* dispatched while bfqq is waiting for its new I/O to
3910	* arrive. This is exactly what may happen if this is a forced
3911	* expiration caused by a preemption attempt, and if bfqq is
3912	* not re-scheduled. To prevent this from happening, re-queue
3913	* bfqq if it needs I/O-dispatch plugging, even if it is
3914	* empty. By doing so, bfqq is granted to be served before the
3915	* above queues (provided that bfqq is of course eligible).
3916	*/
3917	if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
3918	!(reason == BFQQE_PREEMPTED &&
3919	idling_needed_for_service_guarantees(bfqd, bfqq))) {
3920	if (bfqq->dispatched == 0)
3921	/*
3922	* Overloading budget_timeout field to store
3923	* the time at which the queue remains with no
3924	* backlog and no outstanding request; used by
3925	* the weight-raising mechanism.
3926	*/
3927	bfqq->budget_timeout = jiffies;
3928
3929	bfq_del_bfqq_busy(bfqq, expiration: true);
3930	} else {
3931	bfq_requeue_bfqq(bfqd, bfqq, expiration: true);
3932	/*
3933	* Resort priority tree of potential close cooperators.
3934	* See comments on bfq_pos_tree_add_move() for the unlikely().
3935	*/
3936	if (unlikely(!bfqd->nonrot_with_queueing &&
3937	!RB_EMPTY_ROOT(&bfqq->sort_list)))
3938	bfq_pos_tree_add_move(bfqd, bfqq);
3939	}
3940
3941	/*
3942	* All in-service entities must have been properly deactivated
3943	* or requeued before executing the next function, which
3944	* resets all in-service entities as no more in service. This
3945	* may cause bfqq to be freed. If this happens, the next
3946	* function returns true.
3947	*/
3948	return __bfq_bfqd_reset_in_service(bfqd);
3949	}
3950
3951	/**
3952	* __bfq_bfqq_recalc_budget - try to adapt the budget to the @bfqq behavior.
3953	* @bfqd: device data.
3954	* @bfqq: queue to update.
3955	* @reason: reason for expiration.
3956	*
3957	* Handle the feedback on @bfqq budget at queue expiration.
3958	* See the body for detailed comments.
3959	*/
3960	static void __bfq_bfqq_recalc_budget(struct bfq_data *bfqd,
3961	struct bfq_queue *bfqq,
3962	enum bfqq_expiration reason)
3963	{
3964	struct request *next_rq;
3965	int budget, min_budget;
3966
3967	min_budget = bfq_min_budget(bfqd);
3968
3969	if (bfqq->wr_coeff == 1)
3970	budget = bfqq->max_budget;
3971	else /*
3972	* Use a constant, low budget for weight-raised queues,
3973	* to help achieve a low latency. Keep it slightly higher
3974	* than the minimum possible budget, to cause a little
3975	* bit fewer expirations.
3976	*/
3977	budget = 2 * min_budget;
3978
3979	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last budg %d, budg left %d",
3980	bfqq->entity.budget, bfq_bfqq_budget_left(bfqq));
3981	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: last max_budg %d, min budg %d",
3982	budget, bfq_min_budget(bfqd));
3983	bfq_log_bfqq(bfqd, bfqq, "recalc_budg: sync %d, seeky %d",
3984	bfq_bfqq_sync(bfqq), BFQQ_SEEKY(bfqd->in_service_queue));
3985
3986	if (bfq_bfqq_sync(bfqq) && bfqq->wr_coeff == 1) {
3987	switch (reason) {
3988	/*
3989	* Caveat: in all the following cases we trade latency
3990	* for throughput.
3991	*/
3992	case BFQQE_TOO_IDLE:
3993	/*
3994	* This is the only case where we may reduce
3995	* the budget: if there is no request of the
3996	* process still waiting for completion, then
3997	* we assume (tentatively) that the timer has
3998	* expired because the batch of requests of
3999	* the process could have been served with a
4000	* smaller budget. Hence, betting that
4001	* process will behave in the same way when it
4002	* becomes backlogged again, we reduce its
4003	* next budget. As long as we guess right,
4004	* this budget cut reduces the latency
4005	* experienced by the process.
4006	*
4007	* However, if there are still outstanding
4008	* requests, then the process may have not yet
4009	* issued its next request just because it is
4010	* still waiting for the completion of some of
4011	* the still outstanding ones. So in this
4012	* subcase we do not reduce its budget, on the
4013	* contrary we increase it to possibly boost
4014	* the throughput, as discussed in the
4015	* comments to the BUDGET_TIMEOUT case.
4016	*/
4017	if (bfqq->dispatched > 0) /* still outstanding reqs */
4018	budget = min(budget * 2, bfqd->bfq_max_budget);
4019	else {
4020	if (budget > 5 * min_budget)
4021	budget -= 4 * min_budget;
4022	else
4023	budget = min_budget;
4024	}
4025	break;
4026	case BFQQE_BUDGET_TIMEOUT:
4027	/*
4028	* We double the budget here because it gives
4029	* the chance to boost the throughput if this
4030	* is not a seeky process (and has bumped into
4031	* this timeout because of, e.g., ZBR).
4032	*/
4033	budget = min(budget * 2, bfqd->bfq_max_budget);
4034	break;
4035	case BFQQE_BUDGET_EXHAUSTED:
4036	/*
4037	* The process still has backlog, and did not
4038	* let either the budget timeout or the disk
4039	* idling timeout expire. Hence it is not
4040	* seeky, has a short thinktime and may be
4041	* happy with a higher budget too. So
4042	* definitely increase the budget of this good
4043	* candidate to boost the disk throughput.
4044	*/
4045	budget = min(budget * 4, bfqd->bfq_max_budget);
4046	break;
4047	case BFQQE_NO_MORE_REQUESTS:
4048	/*
4049	* For queues that expire for this reason, it
4050	* is particularly important to keep the
4051	* budget close to the actual service they
4052	* need. Doing so reduces the timestamp
4053	* misalignment problem described in the
4054	* comments in the body of
4055	* __bfq_activate_entity. In fact, suppose
4056	* that a queue systematically expires for
4057	* BFQQE_NO_MORE_REQUESTS and presents a
4058	* new request in time to enjoy timestamp
4059	* back-shifting. The larger the budget of the
4060	* queue is with respect to the service the
4061	* queue actually requests in each service
4062	* slot, the more times the queue can be
4063	* reactivated with the same virtual finish
4064	* time. It follows that, even if this finish
4065	* time is pushed to the system virtual time
4066	* to reduce the consequent timestamp
4067	* misalignment, the queue unjustly enjoys for
4068	* many re-activations a lower finish time
4069	* than all newly activated queues.
4070	*
4071	* The service needed by bfqq is measured
4072	* quite precisely by bfqq->entity.service.
4073	* Since bfqq does not enjoy device idling,
4074	* bfqq->entity.service is equal to the number
4075	* of sectors that the process associated with
4076	* bfqq requested to read/write before waiting
4077	* for request completions, or blocking for
4078	* other reasons.
4079	*/
4080	budget = max_t(int, bfqq->entity.service, min_budget);
4081	break;
4082	default:
4083	return;
4084	}
4085	} else if (!bfq_bfqq_sync(bfqq)) {
4086	/*
4087	* Async queues get always the maximum possible
4088	* budget, as for them we do not care about latency
4089	* (in addition, their ability to dispatch is limited
4090	* by the charging factor).
4091	*/
4092	budget = bfqd->bfq_max_budget;
4093	}
4094
4095	bfqq->max_budget = budget;
4096
4097	if (bfqd->budgets_assigned >= bfq_stats_min_budgets &&
4098	!bfqd->bfq_user_max_budget)
4099	bfqq->max_budget = min(bfqq->max_budget, bfqd->bfq_max_budget);
4100
4101	/*
4102	* If there is still backlog, then assign a new budget, making
4103	* sure that it is large enough for the next request. Since
4104	* the finish time of bfqq must be kept in sync with the
4105	* budget, be sure to call __bfq_bfqq_expire() *after* this
4106	* update.
4107	*
4108	* If there is no backlog, then no need to update the budget;
4109	* it will be updated on the arrival of a new request.
4110	*/
4111	next_rq = bfqq->next_rq;
4112	if (next_rq)
4113	bfqq->entity.budget = max_t(unsigned long, bfqq->max_budget,
4114	bfq_serv_to_charge(next_rq, bfqq));
4115
4116	bfq_log_bfqq(bfqd, bfqq, "head sect: %u, new budget %d",
4117	next_rq ? blk_rq_sectors(next_rq) : 0,
4118	bfqq->entity.budget);
4119	}
4120
4121	/*
4122	* Return true if the process associated with bfqq is "slow". The slow
4123	* flag is used, in addition to the budget timeout, to reduce the
4124	* amount of service provided to seeky processes, and thus reduce
4125	* their chances to lower the throughput. More details in the comments
4126	* on the function bfq_bfqq_expire().
4127	*
4128	* An important observation is in order: as discussed in the comments
4129	* on the function bfq_update_peak_rate(), with devices with internal
4130	* queues, it is hard if ever possible to know when and for how long
4131	* an I/O request is processed by the device (apart from the trivial
4132	* I/O pattern where a new request is dispatched only after the
4133	* previous one has been completed). This makes it hard to evaluate
4134	* the real rate at which the I/O requests of each bfq_queue are
4135	* served. In fact, for an I/O scheduler like BFQ, serving a
4136	* bfq_queue means just dispatching its requests during its service
4137	* slot (i.e., until the budget of the queue is exhausted, or the
4138	* queue remains idle, or, finally, a timeout fires). But, during the
4139	* service slot of a bfq_queue, around 100 ms at most, the device may
4140	* be even still processing requests of bfq_queues served in previous
4141	* service slots. On the opposite end, the requests of the in-service
4142	* bfq_queue may be completed after the service slot of the queue
4143	* finishes.
4144	*
4145	* Anyway, unless more sophisticated solutions are used
4146	* (where possible), the sum of the sizes of the requests dispatched
4147	* during the service slot of a bfq_queue is probably the only
4148	* approximation available for the service received by the bfq_queue
4149	* during its service slot. And this sum is the quantity used in this
4150	* function to evaluate the I/O speed of a process.
4151	*/
4152	static bool bfq_bfqq_is_slow(struct bfq_data *bfqd, struct bfq_queue *bfqq,
4153	bool compensate, unsigned long *delta_ms)
4154	{
4155	ktime_t delta_ktime;
4156	u32 delta_usecs;
4157	bool slow = BFQQ_SEEKY(bfqq); /* if delta too short, use seekyness */
4158
4159	if (!bfq_bfqq_sync(bfqq))
4160	return false;
4161
4162	if (compensate)
4163	delta_ktime = bfqd->last_idling_start;
4164	else
4165	delta_ktime = blk_time_get();
4166	delta_ktime = ktime_sub(delta_ktime, bfqd->last_budget_start);
4167	delta_usecs = ktime_to_us(kt: delta_ktime);
4168
4169	/* don't use too short time intervals */
4170	if (delta_usecs < 1000) {
4171	if (blk_queue_nonrot(bfqd->queue))
4172	/*
4173	* give same worst-case guarantees as idling
4174	* for seeky
4175	*/
4176	*delta_ms = BFQ_MIN_TT / NSEC_PER_MSEC;
4177	else /* charge at least one seek */
4178	*delta_ms = bfq_slice_idle / NSEC_PER_MSEC;
4179
4180	return slow;
4181	}
4182
4183	*delta_ms = delta_usecs / USEC_PER_MSEC;
4184
4185	/*
4186	* Use only long (> 20ms) intervals to filter out excessive
4187	* spikes in service rate estimation.
4188	*/
4189	if (delta_usecs > 20000) {
4190	/*
4191	* Caveat for rotational devices: processes doing I/O
4192	* in the slower disk zones tend to be slow(er) even
4193	* if not seeky. In this respect, the estimated peak
4194	* rate is likely to be an average over the disk
4195	* surface. Accordingly, to not be too harsh with
4196	* unlucky processes, a process is deemed slow only if
4197	* its rate has been lower than half of the estimated
4198	* peak rate.
4199	*/
4200	slow = bfqq->entity.service < bfqd->bfq_max_budget / 2;
4201	}
4202
4203	bfq_log_bfqq(bfqd, bfqq, "bfq_bfqq_is_slow: slow %d", slow);
4204
4205	return slow;
4206	}
4207
4208	/*
4209	* To be deemed as soft real-time, an application must meet two
4210	* requirements. First, the application must not require an average
4211	* bandwidth higher than the approximate bandwidth required to playback or
4212	* record a compressed high-definition video.
4213	* The next function is invoked on the completion of the last request of a
4214	* batch, to compute the next-start time instant, soft_rt_next_start, such
4215	* that, if the next request of the application does not arrive before
4216	* soft_rt_next_start, then the above requirement on the bandwidth is met.
4217	*
4218	* The second requirement is that the request pattern of the application is
4219	* isochronous, i.e., that, after issuing a request or a batch of requests,
4220	* the application stops issuing new requests until all its pending requests
4221	* have been completed. After that, the application may issue a new batch,
4222	* and so on.
4223	* For this reason the next function is invoked to compute
4224	* soft_rt_next_start only for applications that meet this requirement,
4225	* whereas soft_rt_next_start is set to infinity for applications that do
4226	* not.
4227	*
4228	* Unfortunately, even a greedy (i.e., I/O-bound) application may
4229	* happen to meet, occasionally or systematically, both the above
4230	* bandwidth and isochrony requirements. This may happen at least in
4231	* the following circumstances. First, if the CPU load is high. The
4232	* application may stop issuing requests while the CPUs are busy
4233	* serving other processes, then restart, then stop again for a while,
4234	* and so on. The other circumstances are related to the storage
4235	* device: the storage device is highly loaded or reaches a low-enough
4236	* throughput with the I/O of the application (e.g., because the I/O
4237	* is random and/or the device is slow). In all these cases, the
4238	* I/O of the application may be simply slowed down enough to meet
4239	* the bandwidth and isochrony requirements. To reduce the probability
4240	* that greedy applications are deemed as soft real-time in these
4241	* corner cases, a further rule is used in the computation of
4242	* soft_rt_next_start: the return value of this function is forced to
4243	* be higher than the maximum between the following two quantities.
4244	*
4245	* (a) Current time plus: (1) the maximum time for which the arrival
4246	* of a request is waited for when a sync queue becomes idle,
4247	* namely bfqd->bfq_slice_idle, and (2) a few extra jiffies. We
4248	* postpone for a moment the reason for adding a few extra
4249	* jiffies; we get back to it after next item (b). Lower-bounding
4250	* the return value of this function with the current time plus
4251	* bfqd->bfq_slice_idle tends to filter out greedy applications,
4252	* because the latter issue their next request as soon as possible
4253	* after the last one has been completed. In contrast, a soft
4254	* real-time application spends some time processing data, after a
4255	* batch of its requests has been completed.
4256	*
4257	* (b) Current value of bfqq->soft_rt_next_start. As pointed out
4258	* above, greedy applications may happen to meet both the
4259	* bandwidth and isochrony requirements under heavy CPU or
4260	* storage-device load. In more detail, in these scenarios, these
4261	* applications happen, only for limited time periods, to do I/O
4262	* slowly enough to meet all the requirements described so far,
4263	* including the filtering in above item (a). These slow-speed
4264	* time intervals are usually interspersed between other time
4265	* intervals during which these applications do I/O at a very high
4266	* speed. Fortunately, exactly because of the high speed of the
4267	* I/O in the high-speed intervals, the values returned by this
4268	* function happen to be so high, near the end of any such
4269	* high-speed interval, to be likely to fall *after* the end of
4270	* the low-speed time interval that follows. These high values are
4271	* stored in bfqq->soft_rt_next_start after each invocation of
4272	* this function. As a consequence, if the last value of
4273	* bfqq->soft_rt_next_start is constantly used to lower-bound the
4274	* next value that this function may return, then, from the very
4275	* beginning of a low-speed interval, bfqq->soft_rt_next_start is
4276	* likely to be constantly kept so high that any I/O request
4277	* issued during the low-speed interval is considered as arriving
4278	* to soon for the application to be deemed as soft
4279	* real-time. Then, in the high-speed interval that follows, the
4280	* application will not be deemed as soft real-time, just because
4281	* it will do I/O at a high speed. And so on.
4282	*
4283	* Getting back to the filtering in item (a), in the following two
4284	* cases this filtering might be easily passed by a greedy
4285	* application, if the reference quantity was just
4286	* bfqd->bfq_slice_idle:
4287	* 1) HZ is so low that the duration of a jiffy is comparable to or
4288	* higher than bfqd->bfq_slice_idle. This happens, e.g., on slow
4289	* devices with HZ=100. The time granularity may be so coarse
4290	* that the approximation, in jiffies, of bfqd->bfq_slice_idle
4291	* is rather lower than the exact value.
4292	* 2) jiffies, instead of increasing at a constant rate, may stop increasing
4293	* for a while, then suddenly 'jump' by several units to recover the lost
4294	* increments. This seems to happen, e.g., inside virtual machines.
4295	* To address this issue, in the filtering in (a) we do not use as a
4296	* reference time interval just bfqd->bfq_slice_idle, but
4297	* bfqd->bfq_slice_idle plus a few jiffies. In particular, we add the
4298	* minimum number of jiffies for which the filter seems to be quite
4299	* precise also in embedded systems and KVM/QEMU virtual machines.
4300	*/
4301	static unsigned long bfq_bfqq_softrt_next_start(struct bfq_data *bfqd,
4302	struct bfq_queue *bfqq)
4303	{
4304	return max3(bfqq->soft_rt_next_start,
4305	bfqq->last_idle_bklogged +
4306	HZ * bfqq->service_from_backlogged /
4307	bfqd->bfq_wr_max_softrt_rate,
4308	jiffies + nsecs_to_jiffies(bfqq->bfqd->bfq_slice_idle) + 4);
4309	}
4310
4311	/**
4312	* bfq_bfqq_expire - expire a queue.
4313	* @bfqd: device owning the queue.
4314	* @bfqq: the queue to expire.
4315	* @compensate: if true, compensate for the time spent idling.
4316	* @reason: the reason causing the expiration.
4317	*
4318	* If the process associated with bfqq does slow I/O (e.g., because it
4319	* issues random requests), we charge bfqq with the time it has been
4320	* in service instead of the service it has received (see
4321	* bfq_bfqq_charge_time for details on how this goal is achieved). As
4322	* a consequence, bfqq will typically get higher timestamps upon
4323	* reactivation, and hence it will be rescheduled as if it had
4324	* received more service than what it has actually received. In the
4325	* end, bfqq receives less service in proportion to how slowly its
4326	* associated process consumes its budgets (and hence how seriously it
4327	* tends to lower the throughput). In addition, this time-charging
4328	* strategy guarantees time fairness among slow processes. In
4329	* contrast, if the process associated with bfqq is not slow, we
4330	* charge bfqq exactly with the service it has received.
4331	*
4332	* Charging time to the first type of queues and the exact service to
4333	* the other has the effect of using the WF2Q+ policy to schedule the
4334	* former on a timeslice basis, without violating service domain
4335	* guarantees among the latter.
4336	*/
4337	void bfq_bfqq_expire(struct bfq_data *bfqd,
4338	struct bfq_queue *bfqq,
4339	bool compensate,
4340	enum bfqq_expiration reason)
4341	{
4342	bool slow;
4343	unsigned long delta = 0;
4344	struct bfq_entity *entity = &bfqq->entity;
4345
4346	/*
4347	* Check whether the process is slow (see bfq_bfqq_is_slow).
4348	*/
4349	slow = bfq_bfqq_is_slow(bfqd, bfqq, compensate, delta_ms: &delta);
4350
4351	/*
4352	* As above explained, charge slow (typically seeky) and
4353	* timed-out queues with the time and not the service
4354	* received, to favor sequential workloads.
4355	*
4356	* Processes doing I/O in the slower disk zones will tend to
4357	* be slow(er) even if not seeky. Therefore, since the
4358	* estimated peak rate is actually an average over the disk
4359	* surface, these processes may timeout just for bad luck. To
4360	* avoid punishing them, do not charge time to processes that
4361	* succeeded in consuming at least 2/3 of their budget. This
4362	* allows BFQ to preserve enough elasticity to still perform
4363	* bandwidth, and not time, distribution with little unlucky
4364	* or quasi-sequential processes.
4365	*/
4366	if (bfqq->wr_coeff == 1 &&
4367	(slow ||
4368	(reason == BFQQE_BUDGET_TIMEOUT &&
4369	bfq_bfqq_budget_left(bfqq) >= entity->budget / 3)))
4370	bfq_bfqq_charge_time(bfqd, bfqq, time_ms: delta);
4371
4372	if (bfqd->low_latency && bfqq->wr_coeff == 1)
4373	bfqq->last_wr_start_finish = jiffies;
4374
4375	if (bfqd->low_latency && bfqd->bfq_wr_max_softrt_rate > 0 &&
4376	RB_EMPTY_ROOT(&bfqq->sort_list)) {
4377	/*
4378	* If we get here, and there are no outstanding
4379	* requests, then the request pattern is isochronous
4380	* (see the comments on the function
4381	* bfq_bfqq_softrt_next_start()). Therefore we can
4382	* compute soft_rt_next_start.
4383	*
4384	* If, instead, the queue still has outstanding
4385	* requests, then we have to wait for the completion
4386	* of all the outstanding requests to discover whether
4387	* the request pattern is actually isochronous.
4388	*/
4389	if (bfqq->dispatched == 0)
4390	bfqq->soft_rt_next_start =
4391	bfq_bfqq_softrt_next_start(bfqd, bfqq);
4392	else if (bfqq->dispatched > 0) {
4393	/*
4394	* Schedule an update of soft_rt_next_start to when
4395	* the task may be discovered to be isochronous.
4396	*/
4397	bfq_mark_bfqq_softrt_update(bfqq);
4398	}
4399	}
4400
4401	bfq_log_bfqq(bfqd, bfqq,
4402	"expire (%d, slow %d, num_disp %d, short_ttime %d)", reason,
4403	slow, bfqq->dispatched, bfq_bfqq_has_short_ttime(bfqq));
4404
4405	/*
4406	* bfqq expired, so no total service time needs to be computed
4407	* any longer: reset state machine for measuring total service
4408	* times.
4409	*/
4410	bfqd->rqs_injected = bfqd->wait_dispatch = false;
4411	bfqd->waited_rq = NULL;
4412
4413	/*
4414	* Increase, decrease or leave budget unchanged according to
4415	* reason.
4416	*/
4417	__bfq_bfqq_recalc_budget(bfqd, bfqq, reason);
4418	if (__bfq_bfqq_expire(bfqd, bfqq, reason))
4419	/* bfqq is gone, no more actions on it */
4420	return;
4421
4422	/* mark bfqq as waiting a request only if a bic still points to it */
4423	if (!bfq_bfqq_busy(bfqq) &&
4424	reason != BFQQE_BUDGET_TIMEOUT &&
4425	reason != BFQQE_BUDGET_EXHAUSTED) {
4426	bfq_mark_bfqq_non_blocking_wait_rq(bfqq);
4427	/*
4428	* Not setting service to 0, because, if the next rq
4429	* arrives in time, the queue will go on receiving
4430	* service with this same budget (as if it never expired)
4431	*/
4432	} else
4433	entity->service = 0;
4434
4435	/*
4436	* Reset the received-service counter for every parent entity.
4437	* Differently from what happens with bfqq->entity.service,
4438	* the resetting of this counter never needs to be postponed
4439	* for parent entities. In fact, in case bfqq may have a
4440	* chance to go on being served using the last, partially
4441	* consumed budget, bfqq->entity.service needs to be kept,
4442	* because if bfqq then actually goes on being served using
4443	* the same budget, the last value of bfqq->entity.service is
4444	* needed to properly decrement bfqq->entity.budget by the
4445	* portion already consumed. In contrast, it is not necessary
4446	* to keep entity->service for parent entities too, because
4447	* the bubble up of the new value of bfqq->entity.budget will
4448	* make sure that the budgets of parent entities are correct,
4449	* even in case bfqq and thus parent entities go on receiving
4450	* service with the same budget.
4451	*/
4452	entity = entity->parent;
4453	for_each_entity(entity)
4454	entity->service = 0;
4455	}
4456
4457	/*
4458	* Budget timeout is not implemented through a dedicated timer, but
4459	* just checked on request arrivals and completions, as well as on
4460	* idle timer expirations.
4461	*/
4462	static bool bfq_bfqq_budget_timeout(struct bfq_queue *bfqq)
4463	{
4464	return time_is_before_eq_jiffies(bfqq->budget_timeout);
4465	}
4466
4467	/*
4468	* If we expire a queue that is actively waiting (i.e., with the
4469	* device idled) for the arrival of a new request, then we may incur
4470	* the timestamp misalignment problem described in the body of the
4471	* function __bfq_activate_entity. Hence we return true only if this
4472	* condition does not hold, or if the queue is slow enough to deserve
4473	* only to be kicked off for preserving a high throughput.
4474	*/
4475	static bool bfq_may_expire_for_budg_timeout(struct bfq_queue *bfqq)
4476	{
4477	bfq_log_bfqq(bfqq->bfqd, bfqq,
4478	"may_budget_timeout: wait_request %d left %d timeout %d",
4479	bfq_bfqq_wait_request(bfqq),
4480	bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3,
4481	bfq_bfqq_budget_timeout(bfqq));
4482
4483	return (!bfq_bfqq_wait_request(bfqq) ||
4484	bfq_bfqq_budget_left(bfqq) >= bfqq->entity.budget / 3)
4485	&&
4486	bfq_bfqq_budget_timeout(bfqq);
4487	}
4488
4489	static bool idling_boosts_thr_without_issues(struct bfq_data *bfqd,
4490	struct bfq_queue *bfqq)
4491	{
4492	bool rot_without_queueing =
4493	!blk_queue_nonrot(bfqd->queue) && !bfqd->hw_tag,
4494	bfqq_sequential_and_IO_bound,
4495	idling_boosts_thr;
4496
4497	/* No point in idling for bfqq if it won't get requests any longer */
4498	if (unlikely(!bfqq_process_refs(bfqq)))
4499	return false;
4500
4501	bfqq_sequential_and_IO_bound = !BFQQ_SEEKY(bfqq) &&
4502	bfq_bfqq_IO_bound(bfqq) && bfq_bfqq_has_short_ttime(bfqq);
4503
4504	/*
4505	* The next variable takes into account the cases where idling
4506	* boosts the throughput.
4507	*
4508	* The value of the variable is computed considering, first, that
4509	* idling is virtually always beneficial for the throughput if:
4510	* (a) the device is not NCQ-capable and rotational, or
4511	* (b) regardless of the presence of NCQ, the device is rotational and
4512	* the request pattern for bfqq is I/O-bound and sequential, or
4513	* (c) regardless of whether it is rotational, the device is
4514	* not NCQ-capable and the request pattern for bfqq is
4515	* I/O-bound and sequential.
4516	*
4517	* Secondly, and in contrast to the above item (b), idling an
4518	* NCQ-capable flash-based device would not boost the
4519	* throughput even with sequential I/O; rather it would lower
4520	* the throughput in proportion to how fast the device
4521	* is. Accordingly, the next variable is true if any of the
4522	* above conditions (a), (b) or (c) is true, and, in
4523	* particular, happens to be false if bfqd is an NCQ-capable
4524	* flash-based device.
4525	*/
4526	idling_boosts_thr = rot_without_queueing ||
4527	((!blk_queue_nonrot(bfqd->queue) || !bfqd->hw_tag) &&
4528	bfqq_sequential_and_IO_bound);
4529
4530	/*
4531	* The return value of this function is equal to that of
4532	* idling_boosts_thr, unless a special case holds. In this
4533	* special case, described below, idling may cause problems to
4534	* weight-raised queues.
4535	*
4536	* When the request pool is saturated (e.g., in the presence
4537	* of write hogs), if the processes associated with
4538	* non-weight-raised queues ask for requests at a lower rate,
4539	* then processes associated with weight-raised queues have a
4540	* higher probability to get a request from the pool
4541	* immediately (or at least soon) when they need one. Thus
4542	* they have a higher probability to actually get a fraction
4543	* of the device throughput proportional to their high
4544	* weight. This is especially true with NCQ-capable drives,
4545	* which enqueue several requests in advance, and further
4546	* reorder internally-queued requests.
4547	*
4548	* For this reason, we force to false the return value if
4549	* there are weight-raised busy queues. In this case, and if
4550	* bfqq is not weight-raised, this guarantees that the device
4551	* is not idled for bfqq (if, instead, bfqq is weight-raised,
4552	* then idling will be guaranteed by another variable, see
4553	* below). Combined with the timestamping rules of BFQ (see
4554	* [1] for details), this behavior causes bfqq, and hence any
4555	* sync non-weight-raised queue, to get a lower number of
4556	* requests served, and thus to ask for a lower number of
4557	* requests from the request pool, before the busy
4558	* weight-raised queues get served again. This often mitigates
4559	* starvation problems in the presence of heavy write
4560	* workloads and NCQ, thereby guaranteeing a higher
4561	* application and system responsiveness in these hostile
4562	* scenarios.
4563	*/
4564	return idling_boosts_thr &&
4565	bfqd->wr_busy_queues == 0;
4566	}
4567
4568	/*
4569	* For a queue that becomes empty, device idling is allowed only if
4570	* this function returns true for that queue. As a consequence, since
4571	* device idling plays a critical role for both throughput boosting
4572	* and service guarantees, the return value of this function plays a
4573	* critical role as well.
4574	*
4575	* In a nutshell, this function returns true only if idling is
4576	* beneficial for throughput or, even if detrimental for throughput,
4577	* idling is however necessary to preserve service guarantees (low
4578	* latency, desired throughput distribution, ...). In particular, on
4579	* NCQ-capable devices, this function tries to return false, so as to
4580	* help keep the drives' internal queues full, whenever this helps the
4581	* device boost the throughput without causing any service-guarantee
4582	* issue.
4583	*
4584	* Most of the issues taken into account to get the return value of
4585	* this function are not trivial. We discuss these issues in the two
4586	* functions providing the main pieces of information needed by this
4587	* function.
4588	*/
4589	static bool bfq_better_to_idle(struct bfq_queue *bfqq)
4590	{
4591	struct bfq_data *bfqd = bfqq->bfqd;
4592	bool idling_boosts_thr_with_no_issue, idling_needed_for_service_guar;
4593
4594	/* No point in idling for bfqq if it won't get requests any longer */
4595	if (unlikely(!bfqq_process_refs(bfqq)))
4596	return false;
4597
4598	if (unlikely(bfqd->strict_guarantees))
4599	return true;
4600
4601	/*
4602	* Idling is performed only if slice_idle > 0. In addition, we
4603	* do not idle if
4604	* (a) bfqq is async
4605	* (b) bfqq is in the idle io prio class: in this case we do
4606	* not idle because we want to minimize the bandwidth that
4607	* queues in this class can steal to higher-priority queues
4608	*/
4609	if (bfqd->bfq_slice_idle == 0 || !bfq_bfqq_sync(bfqq) ||
4610	bfq_class_idle(bfqq))
4611	return false;
4612
4613	idling_boosts_thr_with_no_issue =
4614	idling_boosts_thr_without_issues(bfqd, bfqq);
4615
4616	idling_needed_for_service_guar =
4617	idling_needed_for_service_guarantees(bfqd, bfqq);
4618
4619	/*
4620	* We have now the two components we need to compute the
4621	* return value of the function, which is true only if idling
4622	* either boosts the throughput (without issues), or is
4623	* necessary to preserve service guarantees.
4624	*/
4625	return idling_boosts_thr_with_no_issue ||
4626	idling_needed_for_service_guar;
4627	}
4628
4629	/*
4630	* If the in-service queue is empty but the function bfq_better_to_idle
4631	* returns true, then:
4632	* 1) the queue must remain in service and cannot be expired, and
4633	* 2) the device must be idled to wait for the possible arrival of a new
4634	* request for the queue.
4635	* See the comments on the function bfq_better_to_idle for the reasons
4636	* why performing device idling is the best choice to boost the throughput
4637	* and preserve service guarantees when bfq_better_to_idle itself
4638	* returns true.
4639	*/
4640	static bool bfq_bfqq_must_idle(struct bfq_queue *bfqq)
4641	{
4642	return RB_EMPTY_ROOT(&bfqq->sort_list) && bfq_better_to_idle(bfqq);
4643	}
4644
4645	/*
4646	* This function chooses the queue from which to pick the next extra
4647	* I/O request to inject, if it finds a compatible queue. See the
4648	* comments on bfq_update_inject_limit() for details on the injection
4649	* mechanism, and for the definitions of the quantities mentioned
4650	* below.
4651	*/
4652	static struct bfq_queue *
4653	bfq_choose_bfqq_for_injection(struct bfq_data *bfqd)
4654	{
4655	struct bfq_queue *bfqq, *in_serv_bfqq = bfqd->in_service_queue;
4656	unsigned int limit = in_serv_bfqq->inject_limit;
4657	int i;
4658
4659	/*
4660	* If
4661	* - bfqq is not weight-raised and therefore does not carry
4662	* time-critical I/O,
4663	* or
4664	* - regardless of whether bfqq is weight-raised, bfqq has
4665	* however a long think time, during which it can absorb the
4666	* effect of an appropriate number of extra I/O requests
4667	* from other queues (see bfq_update_inject_limit for
4668	* details on the computation of this number);
4669	* then injection can be performed without restrictions.
4670	*/
4671	bool in_serv_always_inject = in_serv_bfqq->wr_coeff == 1 ||
4672	!bfq_bfqq_has_short_ttime(bfqq: in_serv_bfqq);
4673
4674	/*
4675	* If
4676	* - the baseline total service time could not be sampled yet,
4677	* so the inject limit happens to be still 0, and
4678	* - a lot of time has elapsed since the plugging of I/O
4679	* dispatching started, so drive speed is being wasted
4680	* significantly;
4681	* then temporarily raise inject limit to one request.
4682	*/
4683	if (limit == 0 && in_serv_bfqq->last_serv_time_ns == 0 &&
4684	bfq_bfqq_wait_request(bfqq: in_serv_bfqq) &&
4685	time_is_before_eq_jiffies(bfqd->last_idling_start_jiffies +
4686	bfqd->bfq_slice_idle)
4687	)
4688	limit = 1;
4689
4690	if (bfqd->tot_rq_in_driver >= limit)
4691	return NULL;
4692
4693	/*
4694	* Linear search of the source queue for injection; but, with
4695	* a high probability, very few steps are needed to find a
4696	* candidate queue, i.e., a queue with enough budget left for
4697	* its next request. In fact:
4698	* - BFQ dynamically updates the budget of every queue so as
4699	* to accommodate the expected backlog of the queue;
4700	* - if a queue gets all its requests dispatched as injected
4701	* service, then the queue is removed from the active list
4702	* (and re-added only if it gets new requests, but then it
4703	* is assigned again enough budget for its new backlog).
4704	*/
4705	for (i = 0; i < bfqd->num_actuators; i++) {
4706	list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
4707	if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4708	(in_serv_always_inject || bfqq->wr_coeff > 1) &&
4709	bfq_serv_to_charge(rq: bfqq->next_rq, bfqq) <=
4710	bfq_bfqq_budget_left(bfqq)) {
4711	/*
4712	* Allow for only one large in-flight request
4713	* on non-rotational devices, for the
4714	* following reason. On non-rotationl drives,
4715	* large requests take much longer than
4716	* smaller requests to be served. In addition,
4717	* the drive prefers to serve large requests
4718	* w.r.t. to small ones, if it can choose. So,
4719	* having more than one large requests queued
4720	* in the drive may easily make the next first
4721	* request of the in-service queue wait for so
4722	* long to break bfqq's service guarantees. On
4723	* the bright side, large requests let the
4724	* drive reach a very high throughput, even if
4725	* there is only one in-flight large request
4726	* at a time.
4727	*/
4728	if (blk_queue_nonrot(bfqd->queue) &&
4729	blk_rq_sectors(rq: bfqq->next_rq) >=
4730	BFQQ_SECT_THR_NONROT &&
4731	bfqd->tot_rq_in_driver >= 1)
4732	continue;
4733	else {
4734	bfqd->rqs_injected = true;
4735	return bfqq;
4736	}
4737	}
4738	}
4739
4740	return NULL;
4741	}
4742
4743	static struct bfq_queue *
4744	bfq_find_active_bfqq_for_actuator(struct bfq_data *bfqd, int idx)
4745	{
4746	struct bfq_queue *bfqq;
4747
4748	if (bfqd->in_service_queue &&
4749	bfqd->in_service_queue->actuator_idx == idx)
4750	return bfqd->in_service_queue;
4751
4752	list_for_each_entry(bfqq, &bfqd->active_list[idx], bfqq_list) {
4753	if (!RB_EMPTY_ROOT(&bfqq->sort_list) &&
4754	bfq_serv_to_charge(rq: bfqq->next_rq, bfqq) <=
4755	bfq_bfqq_budget_left(bfqq)) {
4756	return bfqq;
4757	}
4758	}
4759
4760	return NULL;
4761	}
4762
4763	/*
4764	* Perform a linear scan of each actuator, until an actuator is found
4765	* for which the following three conditions hold: the load of the
4766	* actuator is below the threshold (see comments on
4767	* actuator_load_threshold for details) and lower than that of the
4768	* next actuator (comments on this extra condition below), and there
4769	* is a queue that contains I/O for that actuator. On success, return
4770	* that queue.
4771	*
4772	* Performing a plain linear scan entails a prioritization among
4773	* actuators. The extra condition above breaks this prioritization and
4774	* tends to distribute injection uniformly across actuators.
4775	*/
4776	static struct bfq_queue *
4777	bfq_find_bfqq_for_underused_actuator(struct bfq_data *bfqd)
4778	{
4779	int i;
4780
4781	for (i = 0 ; i < bfqd->num_actuators; i++) {
4782	if (bfqd->rq_in_driver[i] < bfqd->actuator_load_threshold &&
4783	(i == bfqd->num_actuators - 1 ||
4784	bfqd->rq_in_driver[i] < bfqd->rq_in_driver[i+1])) {
4785	struct bfq_queue *bfqq =
4786	bfq_find_active_bfqq_for_actuator(bfqd, idx: i);
4787
4788	if (bfqq)
4789	return bfqq;
4790	}
4791	}
4792
4793	return NULL;
4794	}
4795
4796
4797	/*
4798	* Select a queue for service. If we have a current queue in service,
4799	* check whether to continue servicing it, or retrieve and set a new one.
4800	*/
4801	static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
4802	{
4803	struct bfq_queue *bfqq, *inject_bfqq;
4804	struct request *next_rq;
4805	enum bfqq_expiration reason = BFQQE_BUDGET_TIMEOUT;
4806
4807	bfqq = bfqd->in_service_queue;
4808	if (!bfqq)
4809	goto new_queue;
4810
4811	bfq_log_bfqq(bfqd, bfqq, "select_queue: already in-service queue");
4812
4813	/*
4814	* Do not expire bfqq for budget timeout if bfqq may be about
4815	* to enjoy device idling. The reason why, in this case, we
4816	* prevent bfqq from expiring is the same as in the comments
4817	* on the case where bfq_bfqq_must_idle() returns true, in
4818	* bfq_completed_request().
4819	*/
4820	if (bfq_may_expire_for_budg_timeout(bfqq) &&
4821	!bfq_bfqq_must_idle(bfqq))
4822	goto expire;
4823
4824	check_queue:
4825	/*
4826	* If some actuator is underutilized, but the in-service
4827	* queue does not contain I/O for that actuator, then try to
4828	* inject I/O for that actuator.
4829	*/
4830	inject_bfqq = bfq_find_bfqq_for_underused_actuator(bfqd);
4831	if (inject_bfqq && inject_bfqq != bfqq)
4832	return inject_bfqq;
4833
4834	/*
4835	* This loop is rarely executed more than once. Even when it
4836	* happens, it is much more convenient to re-execute this loop
4837	* than to return NULL and trigger a new dispatch to get a
4838	* request served.
4839	*/
4840	next_rq = bfqq->next_rq;
4841	/*
4842	* If bfqq has requests queued and it has enough budget left to
4843	* serve them, keep the queue, otherwise expire it.
4844	*/
4845	if (next_rq) {
4846	if (bfq_serv_to_charge(rq: next_rq, bfqq) >
4847	bfq_bfqq_budget_left(bfqq)) {
4848	/*
4849	* Expire the queue for budget exhaustion,
4850	* which makes sure that the next budget is
4851	* enough to serve the next request, even if
4852	* it comes from the fifo expired path.
4853	*/
4854	reason = BFQQE_BUDGET_EXHAUSTED;
4855	goto expire;
4856	} else {
4857	/*
4858	* The idle timer may be pending because we may
4859	* not disable disk idling even when a new request
4860	* arrives.
4861	*/
4862	if (bfq_bfqq_wait_request(bfqq)) {
4863	/*
4864	* If we get here: 1) at least a new request
4865	* has arrived but we have not disabled the
4866	* timer because the request was too small,
4867	* 2) then the block layer has unplugged
4868	* the device, causing the dispatch to be
4869	* invoked.
4870	*
4871	* Since the device is unplugged, now the
4872	* requests are probably large enough to
4873	* provide a reasonable throughput.
4874	* So we disable idling.
4875	*/
4876	bfq_clear_bfqq_wait_request(bfqq);
4877	hrtimer_try_to_cancel(timer: &bfqd->idle_slice_timer);
4878	}
4879	goto keep_queue;
4880	}
4881	}
4882
4883	/*
4884	* No requests pending. However, if the in-service queue is idling
4885	* for a new request, or has requests waiting for a completion and
4886	* may idle after their completion, then keep it anyway.
4887	*
4888	* Yet, inject service from other queues if it boosts
4889	* throughput and is possible.
4890	*/
4891	if (bfq_bfqq_wait_request(bfqq) ||
4892	(bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
4893	unsigned int act_idx = bfqq->actuator_idx;
4894	struct bfq_queue *async_bfqq = NULL;
4895	struct bfq_queue *blocked_bfqq =
4896	!hlist_empty(h: &bfqq->woken_list) ?
4897	container_of(bfqq->woken_list.first,
4898	struct bfq_queue,
4899	woken_list_node)
4900	: NULL;
4901
4902	if (bfqq->bic && bfqq->bic->bfqq[0][act_idx] &&
4903	bfq_bfqq_busy(bfqq: bfqq->bic->bfqq[0][act_idx]) &&
4904	bfqq->bic->bfqq[0][act_idx]->next_rq)
4905	async_bfqq = bfqq->bic->bfqq[0][act_idx];
4906	/*
4907	* The next four mutually-exclusive ifs decide
4908	* whether to try injection, and choose the queue to
4909	* pick an I/O request from.
4910	*
4911	* The first if checks whether the process associated
4912	* with bfqq has also async I/O pending. If so, it
4913	* injects such I/O unconditionally. Injecting async
4914	* I/O from the same process can cause no harm to the
4915	* process. On the contrary, it can only increase
4916	* bandwidth and reduce latency for the process.
4917	*
4918	* The second if checks whether there happens to be a
4919	* non-empty waker queue for bfqq, i.e., a queue whose
4920	* I/O needs to be completed for bfqq to receive new
4921	* I/O. This happens, e.g., if bfqq is associated with
4922	* a process that does some sync. A sync generates
4923	* extra blocking I/O, which must be completed before
4924	* the process associated with bfqq can go on with its
4925	* I/O. If the I/O of the waker queue is not served,
4926	* then bfqq remains empty, and no I/O is dispatched,
4927	* until the idle timeout fires for bfqq. This is
4928	* likely to result in lower bandwidth and higher
4929	* latencies for bfqq, and in a severe loss of total
4930	* throughput. The best action to take is therefore to
4931	* serve the waker queue as soon as possible. So do it
4932	* (without relying on the third alternative below for
4933	* eventually serving waker_bfqq's I/O; see the last
4934	* paragraph for further details). This systematic
4935	* injection of I/O from the waker queue does not
4936	* cause any delay to bfqq's I/O. On the contrary,
4937	* next bfqq's I/O is brought forward dramatically,
4938	* for it is not blocked for milliseconds.
4939	*
4940	* The third if checks whether there is a queue woken
4941	* by bfqq, and currently with pending I/O. Such a
4942	* woken queue does not steal bandwidth from bfqq,
4943	* because it remains soon without I/O if bfqq is not
4944	* served. So there is virtually no risk of loss of
4945	* bandwidth for bfqq if this woken queue has I/O
4946	* dispatched while bfqq is waiting for new I/O.
4947	*
4948	* The fourth if checks whether bfqq is a queue for
4949	* which it is better to avoid injection. It is so if
4950	* bfqq delivers more throughput when served without
4951	* any further I/O from other queues in the middle, or
4952	* if the service times of bfqq's I/O requests both
4953	* count more than overall throughput, and may be
4954	* easily increased by injection (this happens if bfqq
4955	* has a short think time). If none of these
4956	* conditions holds, then a candidate queue for
4957	* injection is looked for through
4958	* bfq_choose_bfqq_for_injection(). Note that the
4959	* latter may return NULL (for example if the inject
4960	* limit for bfqq is currently 0).
4961	*
4962	* NOTE: motivation for the second alternative
4963	*
4964	* Thanks to the way the inject limit is updated in
4965	* bfq_update_has_short_ttime(), it is rather likely
4966	* that, if I/O is being plugged for bfqq and the
4967	* waker queue has pending I/O requests that are
4968	* blocking bfqq's I/O, then the fourth alternative
4969	* above lets the waker queue get served before the
4970	* I/O-plugging timeout fires. So one may deem the
4971	* second alternative superfluous. It is not, because
4972	* the fourth alternative may be way less effective in
4973	* case of a synchronization. For two main
4974	* reasons. First, throughput may be low because the
4975	* inject limit may be too low to guarantee the same
4976	* amount of injected I/O, from the waker queue or
4977	* other queues, that the second alternative
4978	* guarantees (the second alternative unconditionally
4979	* injects a pending I/O request of the waker queue
4980	* for each bfq_dispatch_request()). Second, with the
4981	* fourth alternative, the duration of the plugging,
4982	* i.e., the time before bfqq finally receives new I/O,
4983	* may not be minimized, because the waker queue may
4984	* happen to be served only after other queues.
4985	*/
4986	if (async_bfqq &&
4987	icq_to_bic(icq: async_bfqq->next_rq->elv.icq) == bfqq->bic &&
4988	bfq_serv_to_charge(rq: async_bfqq->next_rq, bfqq: async_bfqq) <=
4989	bfq_bfqq_budget_left(bfqq: async_bfqq))
4990	bfqq = async_bfqq;
4991	else if (bfqq->waker_bfqq &&
4992	bfq_bfqq_busy(bfqq: bfqq->waker_bfqq) &&
4993	bfqq->waker_bfqq->next_rq &&
4994	bfq_serv_to_charge(rq: bfqq->waker_bfqq->next_rq,
4995	bfqq: bfqq->waker_bfqq) <=
4996	bfq_bfqq_budget_left(bfqq: bfqq->waker_bfqq)
4997	)
4998	bfqq = bfqq->waker_bfqq;
4999	else if (blocked_bfqq &&
5000	bfq_bfqq_busy(bfqq: blocked_bfqq) &&
5001	blocked_bfqq->next_rq &&
5002	bfq_serv_to_charge(rq: blocked_bfqq->next_rq,
5003	bfqq: blocked_bfqq) <=
5004	bfq_bfqq_budget_left(bfqq: blocked_bfqq)
5005	)
5006	bfqq = blocked_bfqq;
5007	else if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
5008	(bfqq->wr_coeff == 1 || bfqd->wr_busy_queues > 1 ||
5009	!bfq_bfqq_has_short_ttime(bfqq)))
5010	bfqq = bfq_choose_bfqq_for_injection(bfqd);
5011	else
5012	bfqq = NULL;
5013
5014	goto keep_queue;
5015	}
5016
5017	reason = BFQQE_NO_MORE_REQUESTS;
5018	expire:
5019	bfq_bfqq_expire(bfqd, bfqq, compensate: false, reason);
5020	new_queue:
5021	bfqq = bfq_set_in_service_queue(bfqd);
5022	if (bfqq) {
5023	bfq_log_bfqq(bfqd, bfqq, "select_queue: checking new queue");
5024	goto check_queue;
5025	}
5026	keep_queue:
5027	if (bfqq)
5028	bfq_log_bfqq(bfqd, bfqq, "select_queue: returned this queue");
5029	else
5030	bfq_log(bfqd, "select_queue: no queue returned");
5031
5032	return bfqq;
5033	}
5034
5035	static void bfq_update_wr_data(struct bfq_data *bfqd, struct bfq_queue *bfqq)
5036	{
5037	struct bfq_entity *entity = &bfqq->entity;
5038
5039	if (bfqq->wr_coeff > 1) { /* queue is being weight-raised */
5040	bfq_log_bfqq(bfqd, bfqq,
5041	"raising period dur %u/%u msec, old coeff %u, w %d(%d)",
5042	jiffies_to_msecs(jiffies - bfqq->last_wr_start_finish),
5043	jiffies_to_msecs(bfqq->wr_cur_max_time),
5044	bfqq->wr_coeff,
5045	bfqq->entity.weight, bfqq->entity.orig_weight);
5046
5047	if (entity->prio_changed)
5048	bfq_log_bfqq(bfqd, bfqq, "WARN: pending prio change");
5049
5050	/*
5051	* If the queue was activated in a burst, or too much
5052	* time has elapsed from the beginning of this
5053	* weight-raising period, then end weight raising.
5054	*/
5055	if (bfq_bfqq_in_large_burst(bfqq))
5056	bfq_bfqq_end_wr(bfqq);
5057	else if (time_is_before_jiffies(bfqq->last_wr_start_finish +
5058	bfqq->wr_cur_max_time)) {
5059	if (bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time ||
5060	time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
5061	bfq_wr_duration(bfqd))) {
5062	/*
5063	* Either in interactive weight
5064	* raising, or in soft_rt weight
5065	* raising with the
5066	* interactive-weight-raising period
5067	* elapsed (so no switch back to
5068	* interactive weight raising).
5069	*/
5070	bfq_bfqq_end_wr(bfqq);
5071	} else { /*
5072	* soft_rt finishing while still in
5073	* interactive period, switch back to
5074	* interactive weight raising
5075	*/
5076	switch_back_to_interactive_wr(bfqq, bfqd);
5077	bfqq->entity.prio_changed = 1;
5078	}
5079	}
5080	if (bfqq->wr_coeff > 1 &&
5081	bfqq->wr_cur_max_time != bfqd->bfq_wr_rt_max_time &&
5082	bfqq->service_from_wr > max_service_from_wr) {
5083	/* see comments on max_service_from_wr */
5084	bfq_bfqq_end_wr(bfqq);
5085	}
5086	}
5087	/*
5088	* To improve latency (for this or other queues), immediately
5089	* update weight both if it must be raised and if it must be
5090	* lowered. Since, entity may be on some active tree here, and
5091	* might have a pending change of its ioprio class, invoke
5092	* next function with the last parameter unset (see the
5093	* comments on the function).
5094	*/
5095	if ((entity->weight > entity->orig_weight) != (bfqq->wr_coeff > 1))
5096	__bfq_entity_update_weight_prio(old_st: bfq_entity_service_tree(entity),
5097	entity, update_class_too: false);
5098	}
5099
5100	/*
5101	* Dispatch next request from bfqq.
5102	*/
5103	static struct request *bfq_dispatch_rq_from_bfqq(struct bfq_data *bfqd,
5104	struct bfq_queue *bfqq)
5105	{
5106	struct request *rq = bfqq->next_rq;
5107	unsigned long service_to_charge;
5108
5109	service_to_charge = bfq_serv_to_charge(rq, bfqq);
5110
5111	bfq_bfqq_served(bfqq, served: service_to_charge);
5112
5113	if (bfqq == bfqd->in_service_queue && bfqd->wait_dispatch) {
5114	bfqd->wait_dispatch = false;
5115	bfqd->waited_rq = rq;
5116	}
5117
5118	bfq_dispatch_remove(q: bfqd->queue, rq);
5119
5120	if (bfqq != bfqd->in_service_queue)
5121	return rq;
5122
5123	/*
5124	* If weight raising has to terminate for bfqq, then next
5125	* function causes an immediate update of bfqq's weight,
5126	* without waiting for next activation. As a consequence, on
5127	* expiration, bfqq will be timestamped as if has never been
5128	* weight-raised during this service slot, even if it has
5129	* received part or even most of the service as a
5130	* weight-raised queue. This inflates bfqq's timestamps, which
5131	* is beneficial, as bfqq is then more willing to leave the
5132	* device immediately to possible other weight-raised queues.
5133	*/
5134	bfq_update_wr_data(bfqd, bfqq);
5135
5136	/*
5137	* Expire bfqq, pretending that its budget expired, if bfqq
5138	* belongs to CLASS_IDLE and other queues are waiting for
5139	* service.
5140	*/
5141	if (bfq_tot_busy_queues(bfqd) > 1 && bfq_class_idle(bfqq))
5142	bfq_bfqq_expire(bfqd, bfqq, compensate: false, reason: BFQQE_BUDGET_EXHAUSTED);
5143
5144	return rq;
5145	}
5146
5147	static bool bfq_has_work(struct blk_mq_hw_ctx *hctx)
5148	{
5149	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5150
5151	/*
5152	* Avoiding lock: a race on bfqd->queued should cause at
5153	* most a call to dispatch for nothing
5154	*/
5155	return !list_empty_careful(head: &bfqd->dispatch) ||
5156	READ_ONCE(bfqd->queued);
5157	}
5158
5159	static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5160	{
5161	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5162	struct request *rq = NULL;
5163	struct bfq_queue *bfqq = NULL;
5164
5165	if (!list_empty(head: &bfqd->dispatch)) {
5166	rq = list_first_entry(&bfqd->dispatch, struct request,
5167	queuelist);
5168	list_del_init(entry: &rq->queuelist);
5169
5170	bfqq = RQ_BFQQ(rq);
5171
5172	if (bfqq) {
5173	/*
5174	* Increment counters here, because this
5175	* dispatch does not follow the standard
5176	* dispatch flow (where counters are
5177	* incremented)
5178	*/
5179	bfqq->dispatched++;
5180
5181	goto inc_in_driver_start_rq;
5182	}
5183
5184	/*
5185	* We exploit the bfq_finish_requeue_request hook to
5186	* decrement tot_rq_in_driver, but
5187	* bfq_finish_requeue_request will not be invoked on
5188	* this request. So, to avoid unbalance, just start
5189	* this request, without incrementing tot_rq_in_driver. As
5190	* a negative consequence, tot_rq_in_driver is deceptively
5191	* lower than it should be while this request is in
5192	* service. This may cause bfq_schedule_dispatch to be
5193	* invoked uselessly.
5194	*
5195	* As for implementing an exact solution, the
5196	* bfq_finish_requeue_request hook, if defined, is
5197	* probably invoked also on this request. So, by
5198	* exploiting this hook, we could 1) increment
5199	* tot_rq_in_driver here, and 2) decrement it in
5200	* bfq_finish_requeue_request. Such a solution would
5201	* let the value of the counter be always accurate,
5202	* but it would entail using an extra interface
5203	* function. This cost seems higher than the benefit,
5204	* being the frequency of non-elevator-private
5205	* requests very low.
5206	*/
5207	goto start_rq;
5208	}
5209
5210	bfq_log(bfqd, "dispatch requests: %d busy queues",
5211	bfq_tot_busy_queues(bfqd));
5212
5213	if (bfq_tot_busy_queues(bfqd) == 0)
5214	goto exit;
5215
5216	/*
5217	* Force device to serve one request at a time if
5218	* strict_guarantees is true. Forcing this service scheme is
5219	* currently the ONLY way to guarantee that the request
5220	* service order enforced by the scheduler is respected by a
5221	* queueing device. Otherwise the device is free even to make
5222	* some unlucky request wait for as long as the device
5223	* wishes.
5224	*
5225	* Of course, serving one request at a time may cause loss of
5226	* throughput.
5227	*/
5228	if (bfqd->strict_guarantees && bfqd->tot_rq_in_driver > 0)
5229	goto exit;
5230
5231	bfqq = bfq_select_queue(bfqd);
5232	if (!bfqq)
5233	goto exit;
5234
5235	rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
5236
5237	if (rq) {
5238	inc_in_driver_start_rq:
5239	bfqd->rq_in_driver[bfqq->actuator_idx]++;
5240	bfqd->tot_rq_in_driver++;
5241	start_rq:
5242	rq->rq_flags |= RQF_STARTED;
5243	}
5244	exit:
5245	return rq;
5246	}
5247
5248	#ifdef CONFIG_BFQ_CGROUP_DEBUG
5249	static void bfq_update_dispatch_stats(struct request_queue *q,
5250	struct request *rq,
5251	struct bfq_queue *in_serv_queue,
5252	bool idle_timer_disabled)
5253	{
5254	struct bfq_queue *bfqq = rq ? RQ_BFQQ(rq) : NULL;
5255
5256	if (!idle_timer_disabled && !bfqq)
5257	return;
5258
5259	/*
5260	* rq and bfqq are guaranteed to exist until this function
5261	* ends, for the following reasons. First, rq can be
5262	* dispatched to the device, and then can be completed and
5263	* freed, only after this function ends. Second, rq cannot be
5264	* merged (and thus freed because of a merge) any longer,
5265	* because it has already started. Thus rq cannot be freed
5266	* before this function ends, and, since rq has a reference to
5267	* bfqq, the same guarantee holds for bfqq too.
5268	*
5269	* In addition, the following queue lock guarantees that
5270	* bfqq_group(bfqq) exists as well.
5271	*/
5272	spin_lock_irq(lock: &q->queue_lock);
5273	if (idle_timer_disabled)
5274	/*
5275	* Since the idle timer has been disabled,
5276	* in_serv_queue contained some request when
5277	* __bfq_dispatch_request was invoked above, which
5278	* implies that rq was picked exactly from
5279	* in_serv_queue. Thus in_serv_queue == bfqq, and is
5280	* therefore guaranteed to exist because of the above
5281	* arguments.
5282	*/
5283	bfqg_stats_update_idle_time(bfqg: bfqq_group(bfqq: in_serv_queue));
5284	if (bfqq) {
5285	struct bfq_group *bfqg = bfqq_group(bfqq);
5286
5287	bfqg_stats_update_avg_queue_size(bfqg);
5288	bfqg_stats_set_start_empty_time(bfqg);
5289	bfqg_stats_update_io_remove(bfqg, opf: rq->cmd_flags);
5290	}
5291	spin_unlock_irq(lock: &q->queue_lock);
5292	}
5293	#else
5294	static inline void bfq_update_dispatch_stats(struct request_queue *q,
5295	struct request *rq,
5296	struct bfq_queue *in_serv_queue,
5297	bool idle_timer_disabled) {}
5298	#endif /* CONFIG_BFQ_CGROUP_DEBUG */
5299
5300	static struct request *bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
5301	{
5302	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
5303	struct request *rq;
5304	struct bfq_queue *in_serv_queue;
5305	bool waiting_rq, idle_timer_disabled = false;
5306
5307	spin_lock_irq(lock: &bfqd->lock);
5308
5309	in_serv_queue = bfqd->in_service_queue;
5310	waiting_rq = in_serv_queue && bfq_bfqq_wait_request(bfqq: in_serv_queue);
5311
5312	rq = __bfq_dispatch_request(hctx);
5313	if (in_serv_queue == bfqd->in_service_queue) {
5314	idle_timer_disabled =
5315	waiting_rq && !bfq_bfqq_wait_request(bfqq: in_serv_queue);
5316	}
5317
5318	spin_unlock_irq(lock: &bfqd->lock);
5319	bfq_update_dispatch_stats(q: hctx->queue, rq,
5320	in_serv_queue: idle_timer_disabled ? in_serv_queue : NULL,
5321	idle_timer_disabled);
5322
5323	return rq;
5324	}
5325
5326	/*
5327	* Task holds one reference to the queue, dropped when task exits. Each rq
5328	* in-flight on this queue also holds a reference, dropped when rq is freed.
5329	*
5330	* Scheduler lock must be held here. Recall not to use bfqq after calling
5331	* this function on it.
5332	*/
5333	void bfq_put_queue(struct bfq_queue *bfqq)
5334	{
5335	struct bfq_queue *item;
5336	struct hlist_node *n;
5337	struct bfq_group *bfqg = bfqq_group(bfqq);
5338
5339	bfq_log_bfqq(bfqq->bfqd, bfqq, "put_queue: %p %d", bfqq, bfqq->ref);
5340
5341	bfqq->ref--;
5342	if (bfqq->ref)
5343	return;
5344
5345	if (!hlist_unhashed(h: &bfqq->burst_list_node)) {
5346	hlist_del_init(n: &bfqq->burst_list_node);
5347	/*
5348	* Decrement also burst size after the removal, if the
5349	* process associated with bfqq is exiting, and thus
5350	* does not contribute to the burst any longer. This
5351	* decrement helps filter out false positives of large
5352	* bursts, when some short-lived process (often due to
5353	* the execution of commands by some service) happens
5354	* to start and exit while a complex application is
5355	* starting, and thus spawning several processes that
5356	* do I/O (and that *must not* be treated as a large
5357	* burst, see comments on bfq_handle_burst).
5358	*
5359	* In particular, the decrement is performed only if:
5360	* 1) bfqq is not a merged queue, because, if it is,
5361	* then this free of bfqq is not triggered by the exit
5362	* of the process bfqq is associated with, but exactly
5363	* by the fact that bfqq has just been merged.
5364	* 2) burst_size is greater than 0, to handle
5365	* unbalanced decrements. Unbalanced decrements may
5366	* happen in te following case: bfqq is inserted into
5367	* the current burst list--without incrementing
5368	* bust_size--because of a split, but the current
5369	* burst list is not the burst list bfqq belonged to
5370	* (see comments on the case of a split in
5371	* bfq_set_request).
5372	*/
5373	if (bfqq->bic && bfqq->bfqd->burst_size > 0)
5374	bfqq->bfqd->burst_size--;
5375	}
5376
5377	/*
5378	* bfqq does not exist any longer, so it cannot be woken by
5379	* any other queue, and cannot wake any other queue. Then bfqq
5380	* must be removed from the woken list of its possible waker
5381	* queue, and all queues in the woken list of bfqq must stop
5382	* having a waker queue. Strictly speaking, these updates
5383	* should be performed when bfqq remains with no I/O source
5384	* attached to it, which happens before bfqq gets freed. In
5385	* particular, this happens when the last process associated
5386	* with bfqq exits or gets associated with a different
5387	* queue. However, both events lead to bfqq being freed soon,
5388	* and dangling references would come out only after bfqq gets
5389	* freed. So these updates are done here, as a simple and safe
5390	* way to handle all cases.
5391	*/
5392	/* remove bfqq from woken list */
5393	if (!hlist_unhashed(h: &bfqq->woken_list_node))
5394	hlist_del_init(n: &bfqq->woken_list_node);
5395
5396	/* reset waker for all queues in woken list */
5397	hlist_for_each_entry_safe(item, n, &bfqq->woken_list,
5398	woken_list_node) {
5399	item->waker_bfqq = NULL;
5400	hlist_del_init(n: &item->woken_list_node);
5401	}
5402
5403	if (bfqq->bfqd->last_completed_rq_bfqq == bfqq)
5404	bfqq->bfqd->last_completed_rq_bfqq = NULL;
5405
5406	WARN_ON_ONCE(!list_empty(&bfqq->fifo));
5407	WARN_ON_ONCE(!RB_EMPTY_ROOT(&bfqq->sort_list));
5408	WARN_ON_ONCE(bfqq->dispatched);
5409
5410	kmem_cache_free(s: bfq_pool, objp: bfqq);
5411	bfqg_and_blkg_put(bfqg);
5412	}
5413
5414	static void bfq_put_stable_ref(struct bfq_queue *bfqq)
5415	{
5416	bfqq->stable_ref--;
5417	bfq_put_queue(bfqq);
5418	}
5419
5420	void bfq_put_cooperator(struct bfq_queue *bfqq)
5421	{
5422	struct bfq_queue *__bfqq, *next;
5423
5424	/*
5425	* If this queue was scheduled to merge with another queue, be
5426	* sure to drop the reference taken on that queue (and others in
5427	* the merge chain). See bfq_setup_merge and bfq_merge_bfqqs.
5428	*/
5429	__bfqq = bfqq->new_bfqq;
5430	while (__bfqq) {
5431	next = __bfqq->new_bfqq;
5432	bfq_put_queue(bfqq: __bfqq);
5433	__bfqq = next;
5434	}
5435	}
5436
5437	static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
5438	{
5439	if (bfqq == bfqd->in_service_queue) {
5440	__bfq_bfqq_expire(bfqd, bfqq, reason: BFQQE_BUDGET_TIMEOUT);
5441	bfq_schedule_dispatch(bfqd);
5442	}
5443
5444	bfq_log_bfqq(bfqd, bfqq, "exit_bfqq: %p, %d", bfqq, bfqq->ref);
5445
5446	bfq_put_cooperator(bfqq);
5447
5448	bfq_release_process_ref(bfqd, bfqq);
5449	}
5450
5451	static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync,
5452	unsigned int actuator_idx)
5453	{
5454	struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, actuator_idx);
5455	struct bfq_data *bfqd;
5456
5457	if (bfqq)
5458	bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
5459
5460	if (bfqq && bfqd) {
5461	bic_set_bfqq(bic, NULL, is_sync, actuator_idx);
5462	bfq_exit_bfqq(bfqd, bfqq);
5463	}
5464	}
5465
5466	static void bfq_exit_icq(struct io_cq *icq)
5467	{
5468	struct bfq_io_cq *bic = icq_to_bic(icq);
5469	struct bfq_data *bfqd = bic_to_bfqd(bic);
5470	unsigned long flags;
5471	unsigned int act_idx;
5472	/*
5473	* If bfqd and thus bfqd->num_actuators is not available any
5474	* longer, then cycle over all possible per-actuator bfqqs in
5475	* next loop. We rely on bic being zeroed on creation, and
5476	* therefore on its unused per-actuator fields being NULL.
5477	*/
5478	unsigned int num_actuators = BFQ_MAX_ACTUATORS;
5479	struct bfq_iocq_bfqq_data *bfqq_data = bic->bfqq_data;
5480
5481	/*
5482	* bfqd is NULL if scheduler already exited, and in that case
5483	* this is the last time these queues are accessed.
5484	*/
5485	if (bfqd) {
5486	spin_lock_irqsave(&bfqd->lock, flags);
5487	num_actuators = bfqd->num_actuators;
5488	}
5489
5490	for (act_idx = 0; act_idx < num_actuators; act_idx++) {
5491	if (bfqq_data[act_idx].stable_merge_bfqq)
5492	bfq_put_stable_ref(bfqq: bfqq_data[act_idx].stable_merge_bfqq);
5493
5494	bfq_exit_icq_bfqq(bic, is_sync: true, actuator_idx: act_idx);
5495	bfq_exit_icq_bfqq(bic, is_sync: false, actuator_idx: act_idx);
5496	}
5497
5498	if (bfqd)
5499	spin_unlock_irqrestore(lock: &bfqd->lock, flags);
5500	}
5501
5502	/*
5503	* Update the entity prio values; note that the new values will not
5504	* be used until the next (re)activation.
5505	*/
5506	static void
5507	bfq_set_next_ioprio_data(struct bfq_queue *bfqq, struct bfq_io_cq *bic)
5508	{
5509	struct task_struct *tsk = current;
5510	int ioprio_class;
5511	struct bfq_data *bfqd = bfqq->bfqd;
5512
5513	if (!bfqd)
5514	return;
5515
5516	ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5517	switch (ioprio_class) {
5518	default:
5519	pr_err("bdi %s: bfq: bad prio class %d\n",
5520	bdi_dev_name(bfqq->bfqd->queue->disk->bdi),
5521	ioprio_class);
5522	fallthrough;
5523	case IOPRIO_CLASS_NONE:
5524	/*
5525	* No prio set, inherit CPU scheduling settings.
5526	*/
5527	bfqq->new_ioprio = task_nice_ioprio(task: tsk);
5528	bfqq->new_ioprio_class = task_nice_ioclass(task: tsk);
5529	break;
5530	case IOPRIO_CLASS_RT:
5531	bfqq->new_ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
5532	bfqq->new_ioprio_class = IOPRIO_CLASS_RT;
5533	break;
5534	case IOPRIO_CLASS_BE:
5535	bfqq->new_ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
5536	bfqq->new_ioprio_class = IOPRIO_CLASS_BE;
5537	break;
5538	case IOPRIO_CLASS_IDLE:
5539	bfqq->new_ioprio_class = IOPRIO_CLASS_IDLE;
5540	bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
5541	break;
5542	}
5543
5544	if (bfqq->new_ioprio >= IOPRIO_NR_LEVELS) {
5545	pr_crit("bfq_set_next_ioprio_data: new_ioprio %d\n",
5546	bfqq->new_ioprio);
5547	bfqq->new_ioprio = IOPRIO_NR_LEVELS - 1;
5548	}
5549
5550	bfqq->entity.new_weight = bfq_ioprio_to_weight(ioprio: bfqq->new_ioprio);
5551	bfq_log_bfqq(bfqd, bfqq, "new_ioprio %d new_weight %d",
5552	bfqq->new_ioprio, bfqq->entity.new_weight);
5553	bfqq->entity.prio_changed = 1;
5554	}
5555
5556	static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5557	struct bio *bio, bool is_sync,
5558	struct bfq_io_cq *bic,
5559	bool respawn);
5560
5561	static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
5562	{
5563	struct bfq_data *bfqd = bic_to_bfqd(bic);
5564	struct bfq_queue *bfqq;
5565	int ioprio = bic->icq.ioc->ioprio;
5566
5567	/*
5568	* This condition may trigger on a newly created bic, be sure to
5569	* drop the lock before returning.
5570	*/
5571	if (unlikely(!bfqd) || likely(bic->ioprio == ioprio))
5572	return;
5573
5574	bic->ioprio = ioprio;
5575
5576	bfqq = bic_to_bfqq(bic, is_sync: false, actuator_idx: bfq_actuator_index(bfqd, bio));
5577	if (bfqq) {
5578	struct bfq_queue *old_bfqq = bfqq;
5579
5580	bfqq = bfq_get_queue(bfqd, bio, is_sync: false, bic, respawn: true);
5581	bic_set_bfqq(bic, bfqq, is_sync: false, actuator_idx: bfq_actuator_index(bfqd, bio));
5582	bfq_release_process_ref(bfqd, bfqq: old_bfqq);
5583	}
5584
5585	bfqq = bic_to_bfqq(bic, is_sync: true, actuator_idx: bfq_actuator_index(bfqd, bio));
5586	if (bfqq)
5587	bfq_set_next_ioprio_data(bfqq, bic);
5588	}
5589
5590	static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5591	struct bfq_io_cq *bic, pid_t pid, int is_sync,
5592	unsigned int act_idx)
5593	{
5594	u64 now_ns = blk_time_get_ns();
5595
5596	bfqq->actuator_idx = act_idx;
5597	RB_CLEAR_NODE(&bfqq->entity.rb_node);
5598	INIT_LIST_HEAD(list: &bfqq->fifo);
5599	INIT_HLIST_NODE(h: &bfqq->burst_list_node);
5600	INIT_HLIST_NODE(h: &bfqq->woken_list_node);
5601	INIT_HLIST_HEAD(&bfqq->woken_list);
5602
5603	bfqq->ref = 0;
5604	bfqq->bfqd = bfqd;
5605
5606	if (bic)
5607	bfq_set_next_ioprio_data(bfqq, bic);
5608
5609	if (is_sync) {
5610	/*
5611	* No need to mark as has_short_ttime if in
5612	* idle_class, because no device idling is performed
5613	* for queues in idle class
5614	*/
5615	if (!bfq_class_idle(bfqq))
5616	/* tentatively mark as has_short_ttime */
5617	bfq_mark_bfqq_has_short_ttime(bfqq);
5618	bfq_mark_bfqq_sync(bfqq);
5619	bfq_mark_bfqq_just_created(bfqq);
5620	} else
5621	bfq_clear_bfqq_sync(bfqq);
5622
5623	/* set end request to minus infinity from now */
5624	bfqq->ttime.last_end_request = now_ns + 1;
5625
5626	bfqq->creation_time = jiffies;
5627
5628	bfqq->io_start_time = now_ns;
5629
5630	bfq_mark_bfqq_IO_bound(bfqq);
5631
5632	bfqq->pid = pid;
5633
5634	/* Tentative initial value to trade off between thr and lat */
5635	bfqq->max_budget = (2 * bfq_max_budget(bfqd)) / 3;
5636	bfqq->budget_timeout = bfq_smallest_from_now();
5637
5638	bfqq->wr_coeff = 1;
5639	bfqq->last_wr_start_finish = jiffies;
5640	bfqq->wr_start_at_switch_to_srt = bfq_smallest_from_now();
5641	bfqq->split_time = bfq_smallest_from_now();
5642
5643	/*
5644	* To not forget the possibly high bandwidth consumed by a
5645	* process/queue in the recent past,
5646	* bfq_bfqq_softrt_next_start() returns a value at least equal
5647	* to the current value of bfqq->soft_rt_next_start (see
5648	* comments on bfq_bfqq_softrt_next_start). Set
5649	* soft_rt_next_start to now, to mean that bfqq has consumed
5650	* no bandwidth so far.
5651	*/
5652	bfqq->soft_rt_next_start = jiffies;
5653
5654	/* first request is almost certainly seeky */
5655	bfqq->seek_history = 1;
5656
5657	bfqq->decrease_time_jif = jiffies;
5658	}
5659
5660	static struct bfq_queue **bfq_async_queue_prio(struct bfq_data *bfqd,
5661	struct bfq_group *bfqg,
5662	int ioprio_class, int ioprio, int act_idx)
5663	{
5664	switch (ioprio_class) {
5665	case IOPRIO_CLASS_RT:
5666	return &bfqg->async_bfqq[0][ioprio][act_idx];
5667	case IOPRIO_CLASS_NONE:
5668	ioprio = IOPRIO_BE_NORM;
5669	fallthrough;
5670	case IOPRIO_CLASS_BE:
5671	return &bfqg->async_bfqq[1][ioprio][act_idx];
5672	case IOPRIO_CLASS_IDLE:
5673	return &bfqg->async_idle_bfqq[act_idx];
5674	default:
5675	return NULL;
5676	}
5677	}
5678
5679	static struct bfq_queue *
5680	bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5681	struct bfq_io_cq *bic,
5682	struct bfq_queue *last_bfqq_created)
5683	{
5684	unsigned int a_idx = last_bfqq_created->actuator_idx;
5685	struct bfq_queue *new_bfqq =
5686	bfq_setup_merge(bfqq, new_bfqq: last_bfqq_created);
5687
5688	if (!new_bfqq)
5689	return bfqq;
5690
5691	if (new_bfqq->bic)
5692	new_bfqq->bic->bfqq_data[a_idx].stably_merged = true;
5693	bic->bfqq_data[a_idx].stably_merged = true;
5694
5695	/*
5696	* Reusing merge functions. This implies that
5697	* bfqq->bic must be set too, for
5698	* bfq_merge_bfqqs to correctly save bfqq's
5699	* state before killing it.
5700	*/
5701	bfqq->bic = bic;
5702	bfq_merge_bfqqs(bfqd, bic, bfqq, new_bfqq);
5703
5704	return new_bfqq;
5705	}
5706
5707	/*
5708	* Many throughput-sensitive workloads are made of several parallel
5709	* I/O flows, with all flows generated by the same application, or
5710	* more generically by the same task (e.g., system boot). The most
5711	* counterproductive action with these workloads is plugging I/O
5712	* dispatch when one of the bfq_queues associated with these flows
5713	* remains temporarily empty.
5714	*
5715	* To avoid this plugging, BFQ has been using a burst-handling
5716	* mechanism for years now. This mechanism has proven effective for
5717	* throughput, and not detrimental for service guarantees. The
5718	* following function pushes this mechanism a little bit further,
5719	* basing on the following two facts.
5720	*
5721	* First, all the I/O flows of a the same application or task
5722	* contribute to the execution/completion of that common application
5723	* or task. So the performance figures that matter are total
5724	* throughput of the flows and task-wide I/O latency. In particular,
5725	* these flows do not need to be protected from each other, in terms
5726	* of individual bandwidth or latency.
5727	*
5728	* Second, the above fact holds regardless of the number of flows.
5729	*
5730	* Putting these two facts together, this commits merges stably the
5731	* bfq_queues associated with these I/O flows, i.e., with the
5732	* processes that generate these IO/ flows, regardless of how many the
5733	* involved processes are.
5734	*
5735	* To decide whether a set of bfq_queues is actually associated with
5736	* the I/O flows of a common application or task, and to merge these
5737	* queues stably, this function operates as follows: given a bfq_queue,
5738	* say Q2, currently being created, and the last bfq_queue, say Q1,
5739	* created before Q2, Q2 is merged stably with Q1 if
5740	* - very little time has elapsed since when Q1 was created
5741	* - Q2 has the same ioprio as Q1
5742	* - Q2 belongs to the same group as Q1
5743	*
5744	* Merging bfq_queues also reduces scheduling overhead. A fio test
5745	* with ten random readers on /dev/nullb shows a throughput boost of
5746	* 40%, with a quadcore. Since BFQ's execution time amounts to ~50% of
5747	* the total per-request processing time, the above throughput boost
5748	* implies that BFQ's overhead is reduced by more than 50%.
5749	*
5750	* This new mechanism most certainly obsoletes the current
5751	* burst-handling heuristics. We keep those heuristics for the moment.
5752	*/
5753	static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
5754	struct bfq_queue *bfqq,
5755	struct bfq_io_cq *bic)
5756	{
5757	struct bfq_queue **source_bfqq = bfqq->entity.parent ?
5758	&bfqq->entity.parent->last_bfqq_created :
5759	&bfqd->last_bfqq_created;
5760
5761	struct bfq_queue *last_bfqq_created = *source_bfqq;
5762
5763	/*
5764	* If last_bfqq_created has not been set yet, then init it. If
5765	* it has been set already, but too long ago, then move it
5766	* forward to bfqq. Finally, move also if bfqq belongs to a
5767	* different group than last_bfqq_created, or if bfqq has a
5768	* different ioprio, ioprio_class or actuator_idx. If none of
5769	* these conditions holds true, then try an early stable merge
5770	* or schedule a delayed stable merge. As for the condition on
5771	* actuator_idx, the reason is that, if queues associated with
5772	* different actuators are merged, then control is lost on
5773	* each actuator. Therefore some actuator may be
5774	* underutilized, and throughput may decrease.
5775	*
5776	* A delayed merge is scheduled (instead of performing an
5777	* early merge), in case bfqq might soon prove to be more
5778	* throughput-beneficial if not merged. Currently this is
5779	* possible only if bfqd is rotational with no queueing. For
5780	* such a drive, not merging bfqq is better for throughput if
5781	* bfqq happens to contain sequential I/O. So, we wait a
5782	* little bit for enough I/O to flow through bfqq. After that,
5783	* if such an I/O is sequential, then the merge is
5784	* canceled. Otherwise the merge is finally performed.
5785	*/
5786	if (!last_bfqq_created ||
5787	time_before(last_bfqq_created->creation_time +
5788	msecs_to_jiffies(bfq_activation_stable_merging),
5789	bfqq->creation_time) ||
5790	bfqq->entity.parent != last_bfqq_created->entity.parent ||
5791	bfqq->ioprio != last_bfqq_created->ioprio ||
5792	bfqq->ioprio_class != last_bfqq_created->ioprio_class ||
5793	bfqq->actuator_idx != last_bfqq_created->actuator_idx)
5794	*source_bfqq = bfqq;
5795	else if (time_after_eq(last_bfqq_created->creation_time +
5796	bfqd->bfq_burst_interval,
5797	bfqq->creation_time)) {
5798	if (likely(bfqd->nonrot_with_queueing))
5799	/*
5800	* With this type of drive, leaving
5801	* bfqq alone may provide no
5802	* throughput benefits compared with
5803	* merging bfqq. So merge bfqq now.
5804	*/
5805	bfqq = bfq_do_early_stable_merge(bfqd, bfqq,
5806	bic,
5807	last_bfqq_created);
5808	else { /* schedule tentative stable merge */
5809	/*
5810	* get reference on last_bfqq_created,
5811	* to prevent it from being freed,
5812	* until we decide whether to merge
5813	*/
5814	last_bfqq_created->ref++;
5815	/*
5816	* need to keep track of stable refs, to
5817	* compute process refs correctly
5818	*/
5819	last_bfqq_created->stable_ref++;
5820	/*
5821	* Record the bfqq to merge to.
5822	*/
5823	bic->bfqq_data[last_bfqq_created->actuator_idx].stable_merge_bfqq =
5824	last_bfqq_created;
5825	}
5826	}
5827
5828	return bfqq;
5829	}
5830
5831
5832	static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
5833	struct bio *bio, bool is_sync,
5834	struct bfq_io_cq *bic,
5835	bool respawn)
5836	{
5837	const int ioprio = IOPRIO_PRIO_LEVEL(bic->ioprio);
5838	const int ioprio_class = IOPRIO_PRIO_CLASS(bic->ioprio);
5839	struct bfq_queue **async_bfqq = NULL;
5840	struct bfq_queue *bfqq;
5841	struct bfq_group *bfqg;
5842
5843	bfqg = bfq_bio_bfqg(bfqd, bio);
5844	if (!is_sync) {
5845	async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
5846	ioprio,
5847	act_idx: bfq_actuator_index(bfqd, bio));
5848	bfqq = *async_bfqq;
5849	if (bfqq)
5850	goto out;
5851	}
5852
5853	bfqq = kmem_cache_alloc_node(s: bfq_pool,
5854	GFP_NOWAIT | __GFP_ZERO | __GFP_NOWARN,
5855	node: bfqd->queue->node);
5856
5857	if (bfqq) {
5858	bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
5859	is_sync, act_idx: bfq_actuator_index(bfqd, bio));
5860	bfq_init_entity(entity: &bfqq->entity, bfqg);
5861	bfq_log_bfqq(bfqd, bfqq, "allocated");
5862	} else {
5863	bfqq = &bfqd->oom_bfqq;
5864	bfq_log_bfqq(bfqd, bfqq, "using oom bfqq");
5865	goto out;
5866	}
5867
5868	/*
5869	* Pin the queue now that it's allocated, scheduler exit will
5870	* prune it.
5871	*/
5872	if (async_bfqq) {
5873	bfqq->ref++; /*
5874	* Extra group reference, w.r.t. sync
5875	* queue. This extra reference is removed
5876	* only if bfqq->bfqg disappears, to
5877	* guarantee that this queue is not freed
5878	* until its group goes away.
5879	*/
5880	bfq_log_bfqq(bfqd, bfqq, "get_queue, bfqq not in async: %p, %d",
5881	bfqq, bfqq->ref);
5882	*async_bfqq = bfqq;
5883	}
5884
5885	out:
5886	bfqq->ref++; /* get a process reference to this queue */
5887
5888	if (bfqq != &bfqd->oom_bfqq && is_sync && !respawn)
5889	bfqq = bfq_do_or_sched_stable_merge(bfqd, bfqq, bic);
5890	return bfqq;
5891	}
5892
5893	static void bfq_update_io_thinktime(struct bfq_data *bfqd,
5894	struct bfq_queue *bfqq)
5895	{
5896	struct bfq_ttime *ttime = &bfqq->ttime;
5897	u64 elapsed;
5898
5899	/*
5900	* We are really interested in how long it takes for the queue to
5901	* become busy when there is no outstanding IO for this queue. So
5902	* ignore cases when the bfq queue has already IO queued.
5903	*/
5904	if (bfqq->dispatched || bfq_bfqq_busy(bfqq))
5905	return;
5906	elapsed = blk_time_get_ns() - bfqq->ttime.last_end_request;
5907	elapsed = min_t(u64, elapsed, 2ULL * bfqd->bfq_slice_idle);
5908
5909	ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
5910	ttime->ttime_total = div_u64(dividend: 7*ttime->ttime_total + 256*elapsed, divisor: 8);
5911	ttime->ttime_mean = div64_ul(ttime->ttime_total + 128,
5912	ttime->ttime_samples);
5913	}
5914
5915	static void
5916	bfq_update_io_seektime(struct bfq_data *bfqd, struct bfq_queue *bfqq,
5917	struct request *rq)
5918	{
5919	bfqq->seek_history <<= 1;
5920	bfqq->seek_history |= BFQ_RQ_SEEKY(bfqd, bfqq->last_request_pos, rq);
5921
5922	if (bfqq->wr_coeff > 1 &&
5923	bfqq->wr_cur_max_time == bfqd->bfq_wr_rt_max_time &&
5924	BFQQ_TOTALLY_SEEKY(bfqq)) {
5925	if (time_is_before_jiffies(bfqq->wr_start_at_switch_to_srt +
5926	bfq_wr_duration(bfqd))) {
5927	/*
5928	* In soft_rt weight raising with the
5929	* interactive-weight-raising period
5930	* elapsed (so no switch back to
5931	* interactive weight raising).
5932	*/
5933	bfq_bfqq_end_wr(bfqq);
5934	} else { /*
5935	* stopping soft_rt weight raising
5936	* while still in interactive period,
5937	* switch back to interactive weight
5938	* raising
5939	*/
5940	switch_back_to_interactive_wr(bfqq, bfqd);
5941	bfqq->entity.prio_changed = 1;
5942	}
5943	}
5944	}
5945
5946	static void bfq_update_has_short_ttime(struct bfq_data *bfqd,
5947	struct bfq_queue *bfqq,
5948	struct bfq_io_cq *bic)
5949	{
5950	bool has_short_ttime = true, state_changed;
5951
5952	/*
5953	* No need to update has_short_ttime if bfqq is async or in
5954	* idle io prio class, or if bfq_slice_idle is zero, because
5955	* no device idling is performed for bfqq in this case.
5956	*/
5957	if (!bfq_bfqq_sync(bfqq) || bfq_class_idle(bfqq) ||
5958	bfqd->bfq_slice_idle == 0)
5959	return;
5960
5961	/* Idle window just restored, statistics are meaningless. */
5962	if (time_is_after_eq_jiffies(bfqq->split_time +
5963	bfqd->bfq_wr_min_idle_time))
5964	return;
5965
5966	/* Think time is infinite if no process is linked to
5967	* bfqq. Otherwise check average think time to decide whether
5968	* to mark as has_short_ttime. To this goal, compare average
5969	* think time with half the I/O-plugging timeout.
5970	*/
5971	if (atomic_read(v: &bic->icq.ioc->active_ref) == 0 ||
5972	(bfq_sample_valid(bfqq->ttime.ttime_samples) &&
5973	bfqq->ttime.ttime_mean > bfqd->bfq_slice_idle>>1))
5974	has_short_ttime = false;
5975
5976	state_changed = has_short_ttime != bfq_bfqq_has_short_ttime(bfqq);
5977
5978	if (has_short_ttime)
5979	bfq_mark_bfqq_has_short_ttime(bfqq);
5980	else
5981	bfq_clear_bfqq_has_short_ttime(bfqq);
5982
5983	/*
5984	* Until the base value for the total service time gets
5985	* finally computed for bfqq, the inject limit does depend on
5986	* the think-time state (short|long). In particular, the limit
5987	* is 0 or 1 if the think time is deemed, respectively, as
5988	* short or long (details in the comments in
5989	* bfq_update_inject_limit()). Accordingly, the next
5990	* instructions reset the inject limit if the think-time state
5991	* has changed and the above base value is still to be
5992	* computed.
5993	*
5994	* However, the reset is performed only if more than 100 ms
5995	* have elapsed since the last update of the inject limit, or
5996	* (inclusive) if the change is from short to long think
5997	* time. The reason for this waiting is as follows.
5998	*
5999	* bfqq may have a long think time because of a
6000	* synchronization with some other queue, i.e., because the
6001	* I/O of some other queue may need to be completed for bfqq
6002	* to receive new I/O. Details in the comments on the choice
6003	* of the queue for injection in bfq_select_queue().
6004	*
6005	* As stressed in those comments, if such a synchronization is
6006	* actually in place, then, without injection on bfqq, the
6007	* blocking I/O cannot happen to served while bfqq is in
6008	* service. As a consequence, if bfqq is granted
6009	* I/O-dispatch-plugging, then bfqq remains empty, and no I/O
6010	* is dispatched, until the idle timeout fires. This is likely
6011	* to result in lower bandwidth and higher latencies for bfqq,
6012	* and in a severe loss of total throughput.
6013	*
6014	* On the opposite end, a non-zero inject limit may allow the
6015	* I/O that blocks bfqq to be executed soon, and therefore
6016	* bfqq to receive new I/O soon.
6017	*
6018	* But, if the blocking gets actually eliminated, then the
6019	* next think-time sample for bfqq may be very low. This in
6020	* turn may cause bfqq's think time to be deemed
6021	* short. Without the 100 ms barrier, this new state change
6022	* would cause the body of the next if to be executed
6023	* immediately. But this would set to 0 the inject
6024	* limit. Without injection, the blocking I/O would cause the
6025	* think time of bfqq to become long again, and therefore the
6026	* inject limit to be raised again, and so on. The only effect
6027	* of such a steady oscillation between the two think-time
6028	* states would be to prevent effective injection on bfqq.
6029	*
6030	* In contrast, if the inject limit is not reset during such a
6031	* long time interval as 100 ms, then the number of short
6032	* think time samples can grow significantly before the reset
6033	* is performed. As a consequence, the think time state can
6034	* become stable before the reset. Therefore there will be no
6035	* state change when the 100 ms elapse, and no reset of the
6036	* inject limit. The inject limit remains steadily equal to 1
6037	* both during and after the 100 ms. So injection can be
6038	* performed at all times, and throughput gets boosted.
6039	*
6040	* An inject limit equal to 1 is however in conflict, in
6041	* general, with the fact that the think time of bfqq is
6042	* short, because injection may be likely to delay bfqq's I/O
6043	* (as explained in the comments in
6044	* bfq_update_inject_limit()). But this does not happen in
6045	* this special case, because bfqq's low think time is due to
6046	* an effective handling of a synchronization, through
6047	* injection. In this special case, bfqq's I/O does not get
6048	* delayed by injection; on the contrary, bfqq's I/O is
6049	* brought forward, because it is not blocked for
6050	* milliseconds.
6051	*
6052	* In addition, serving the blocking I/O much sooner, and much
6053	* more frequently than once per I/O-plugging timeout, makes
6054	* it much quicker to detect a waker queue (the concept of
6055	* waker queue is defined in the comments in
6056	* bfq_add_request()). This makes it possible to start sooner
6057	* to boost throughput more effectively, by injecting the I/O
6058	* of the waker queue unconditionally on every
6059	* bfq_dispatch_request().
6060	*
6061	* One last, important benefit of not resetting the inject
6062	* limit before 100 ms is that, during this time interval, the
6063	* base value for the total service time is likely to get
6064	* finally computed for bfqq, freeing the inject limit from
6065	* its relation with the think time.
6066	*/
6067	if (state_changed && bfqq->last_serv_time_ns == 0 &&
6068	(time_is_before_eq_jiffies(bfqq->decrease_time_jif +
6069	msecs_to_jiffies(100)) ||
6070	!has_short_ttime))
6071	bfq_reset_inject_limit(bfqd, bfqq);
6072	}
6073
6074	/*
6075	* Called when a new fs request (rq) is added to bfqq. Check if there's
6076	* something we should do about it.
6077	*/
6078	static void bfq_rq_enqueued(struct bfq_data *bfqd, struct bfq_queue *bfqq,
6079	struct request *rq)
6080	{
6081	if (rq->cmd_flags & REQ_META)
6082	bfqq->meta_pending++;
6083
6084	bfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
6085
6086	if (bfqq == bfqd->in_service_queue && bfq_bfqq_wait_request(bfqq)) {
6087	bool small_req = bfqq->queued[rq_is_sync(rq)] == 1 &&
6088	blk_rq_sectors(rq) < 32;
6089	bool budget_timeout = bfq_bfqq_budget_timeout(bfqq);
6090
6091	/*
6092	* There is just this request queued: if
6093	* - the request is small, and
6094	* - we are idling to boost throughput, and
6095	* - the queue is not to be expired,
6096	* then just exit.
6097	*
6098	* In this way, if the device is being idled to wait
6099	* for a new request from the in-service queue, we
6100	* avoid unplugging the device and committing the
6101	* device to serve just a small request. In contrast
6102	* we wait for the block layer to decide when to
6103	* unplug the device: hopefully, new requests will be
6104	* merged to this one quickly, then the device will be
6105	* unplugged and larger requests will be dispatched.
6106	*/
6107	if (small_req && idling_boosts_thr_without_issues(bfqd, bfqq) &&
6108	!budget_timeout)
6109	return;
6110
6111	/*
6112	* A large enough request arrived, or idling is being
6113	* performed to preserve service guarantees, or
6114	* finally the queue is to be expired: in all these
6115	* cases disk idling is to be stopped, so clear
6116	* wait_request flag and reset timer.
6117	*/
6118	bfq_clear_bfqq_wait_request(bfqq);
6119	hrtimer_try_to_cancel(timer: &bfqd->idle_slice_timer);
6120
6121	/*
6122	* The queue is not empty, because a new request just
6123	* arrived. Hence we can safely expire the queue, in
6124	* case of budget timeout, without risking that the
6125	* timestamps of the queue are not updated correctly.
6126	* See [1] for more details.
6127	*/
6128	if (budget_timeout)
6129	bfq_bfqq_expire(bfqd, bfqq, compensate: false,
6130	reason: BFQQE_BUDGET_TIMEOUT);
6131	}
6132	}
6133
6134	static void bfqq_request_allocated(struct bfq_queue *bfqq)
6135	{
6136	struct bfq_entity *entity = &bfqq->entity;
6137
6138	for_each_entity(entity)
6139	entity->allocated++;
6140	}
6141
6142	static void bfqq_request_freed(struct bfq_queue *bfqq)
6143	{
6144	struct bfq_entity *entity = &bfqq->entity;
6145
6146	for_each_entity(entity)
6147	entity->allocated--;
6148	}
6149
6150	/* returns true if it causes the idle timer to be disabled */
6151	static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
6152	{
6153	struct bfq_queue *bfqq = RQ_BFQQ(rq),
6154	*new_bfqq = bfq_setup_cooperator(bfqd, bfqq, io_struct: rq, request: true,
6155	RQ_BIC(rq));
6156	bool waiting, idle_timer_disabled = false;
6157
6158	if (new_bfqq) {
6159	/*
6160	* Release the request's reference to the old bfqq
6161	* and make sure one is taken to the shared queue.
6162	*/
6163	bfqq_request_allocated(bfqq: new_bfqq);
6164	bfqq_request_freed(bfqq);
6165	new_bfqq->ref++;
6166	/*
6167	* If the bic associated with the process
6168	* issuing this request still points to bfqq
6169	* (and thus has not been already redirected
6170	* to new_bfqq or even some other bfq_queue),
6171	* then complete the merge and redirect it to
6172	* new_bfqq.
6173	*/
6174	if (bic_to_bfqq(RQ_BIC(rq), is_sync: true,
6175	actuator_idx: bfq_actuator_index(bfqd, bio: rq->bio)) == bfqq)
6176	bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
6177	bfqq, new_bfqq);
6178
6179	bfq_clear_bfqq_just_created(bfqq);
6180	/*
6181	* rq is about to be enqueued into new_bfqq,
6182	* release rq reference on bfqq
6183	*/
6184	bfq_put_queue(bfqq);
6185	rq->elv.priv[1] = new_bfqq;
6186	bfqq = new_bfqq;
6187	}
6188
6189	bfq_update_io_thinktime(bfqd, bfqq);
6190	bfq_update_has_short_ttime(bfqd, bfqq, RQ_BIC(rq));
6191	bfq_update_io_seektime(bfqd, bfqq, rq);
6192
6193	waiting = bfqq && bfq_bfqq_wait_request(bfqq);
6194	bfq_add_request(rq);
6195	idle_timer_disabled = waiting && !bfq_bfqq_wait_request(bfqq);
6196
6197	rq->fifo_time = blk_time_get_ns() + bfqd->bfq_fifo_expire[rq_is_sync(rq)];
6198	list_add_tail(new: &rq->queuelist, head: &bfqq->fifo);
6199
6200	bfq_rq_enqueued(bfqd, bfqq, rq);
6201
6202	return idle_timer_disabled;
6203	}
6204
6205	#ifdef CONFIG_BFQ_CGROUP_DEBUG
6206	static void bfq_update_insert_stats(struct request_queue *q,
6207	struct bfq_queue *bfqq,
6208	bool idle_timer_disabled,
6209	blk_opf_t cmd_flags)
6210	{
6211	if (!bfqq)
6212	return;
6213
6214	/*
6215	* bfqq still exists, because it can disappear only after
6216	* either it is merged with another queue, or the process it
6217	* is associated with exits. But both actions must be taken by
6218	* the same process currently executing this flow of
6219	* instructions.
6220	*
6221	* In addition, the following queue lock guarantees that
6222	* bfqq_group(bfqq) exists as well.
6223	*/
6224	spin_lock_irq(lock: &q->queue_lock);
6225	bfqg_stats_update_io_add(bfqg: bfqq_group(bfqq), bfqq, opf: cmd_flags);
6226	if (idle_timer_disabled)
6227	bfqg_stats_update_idle_time(bfqg: bfqq_group(bfqq));
6228	spin_unlock_irq(lock: &q->queue_lock);
6229	}
6230	#else
6231	static inline void bfq_update_insert_stats(struct request_queue *q,
6232	struct bfq_queue *bfqq,
6233	bool idle_timer_disabled,
6234	blk_opf_t cmd_flags) {}
6235	#endif /* CONFIG_BFQ_CGROUP_DEBUG */
6236
6237	static struct bfq_queue *bfq_init_rq(struct request *rq);
6238
6239	static void bfq_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
6240	blk_insert_t flags)
6241	{
6242	struct request_queue *q = hctx->queue;
6243	struct bfq_data *bfqd = q->elevator->elevator_data;
6244	struct bfq_queue *bfqq;
6245	bool idle_timer_disabled = false;
6246	blk_opf_t cmd_flags;
6247	LIST_HEAD(free);
6248
6249	#ifdef CONFIG_BFQ_GROUP_IOSCHED
6250	if (!cgroup_subsys_on_dfl(io_cgrp_subsys) && rq->bio)
6251	bfqg_stats_update_legacy_io(q, rq);
6252	#endif
6253	spin_lock_irq(lock: &bfqd->lock);
6254	bfqq = bfq_init_rq(rq);
6255	if (blk_mq_sched_try_insert_merge(q, rq, free: &free)) {
6256	spin_unlock_irq(lock: &bfqd->lock);
6257	blk_mq_free_requests(list: &free);
6258	return;
6259	}
6260
6261	trace_block_rq_insert(rq);
6262
6263	if (flags & BLK_MQ_INSERT_AT_HEAD) {
6264	list_add(new: &rq->queuelist, head: &bfqd->dispatch);
6265	} else if (!bfqq) {
6266	list_add_tail(new: &rq->queuelist, head: &bfqd->dispatch);
6267	} else {
6268	idle_timer_disabled = __bfq_insert_request(bfqd, rq);
6269	/*
6270	* Update bfqq, because, if a queue merge has occurred
6271	* in __bfq_insert_request, then rq has been
6272	* redirected into a new queue.
6273	*/
6274	bfqq = RQ_BFQQ(rq);
6275
6276	if (rq_mergeable(rq)) {
6277	elv_rqhash_add(q, rq);
6278	if (!q->last_merge)
6279	q->last_merge = rq;
6280	}
6281	}
6282
6283	/*
6284	* Cache cmd_flags before releasing scheduler lock, because rq
6285	* may disappear afterwards (for example, because of a request
6286	* merge).
6287	*/
6288	cmd_flags = rq->cmd_flags;
6289	spin_unlock_irq(lock: &bfqd->lock);
6290
6291	bfq_update_insert_stats(q, bfqq, idle_timer_disabled,
6292	cmd_flags);
6293	}
6294
6295	static void bfq_insert_requests(struct blk_mq_hw_ctx *hctx,
6296	struct list_head *list,
6297	blk_insert_t flags)
6298	{
6299	while (!list_empty(head: list)) {
6300	struct request *rq;
6301
6302	rq = list_first_entry(list, struct request, queuelist);
6303	list_del_init(entry: &rq->queuelist);
6304	bfq_insert_request(hctx, rq, flags);
6305	}
6306	}
6307
6308	static void bfq_update_hw_tag(struct bfq_data *bfqd)
6309	{
6310	struct bfq_queue *bfqq = bfqd->in_service_queue;
6311
6312	bfqd->max_rq_in_driver = max_t(int, bfqd->max_rq_in_driver,
6313	bfqd->tot_rq_in_driver);
6314
6315	if (bfqd->hw_tag == 1)
6316	return;
6317
6318	/*
6319	* This sample is valid if the number of outstanding requests
6320	* is large enough to allow a queueing behavior. Note that the
6321	* sum is not exact, as it's not taking into account deactivated
6322	* requests.
6323	*/
6324	if (bfqd->tot_rq_in_driver + bfqd->queued <= BFQ_HW_QUEUE_THRESHOLD)
6325	return;
6326
6327	/*
6328	* If active queue hasn't enough requests and can idle, bfq might not
6329	* dispatch sufficient requests to hardware. Don't zero hw_tag in this
6330	* case
6331	*/
6332	if (bfqq && bfq_bfqq_has_short_ttime(bfqq) &&
6333	bfqq->dispatched + bfqq->queued[0] + bfqq->queued[1] <
6334	BFQ_HW_QUEUE_THRESHOLD &&
6335	bfqd->tot_rq_in_driver < BFQ_HW_QUEUE_THRESHOLD)
6336	return;
6337
6338	if (bfqd->hw_tag_samples++ < BFQ_HW_QUEUE_SAMPLES)
6339	return;
6340
6341	bfqd->hw_tag = bfqd->max_rq_in_driver > BFQ_HW_QUEUE_THRESHOLD;
6342	bfqd->max_rq_in_driver = 0;
6343	bfqd->hw_tag_samples = 0;
6344
6345	bfqd->nonrot_with_queueing =
6346	blk_queue_nonrot(bfqd->queue) && bfqd->hw_tag;
6347	}
6348
6349	static void bfq_completed_request(struct bfq_queue *bfqq, struct bfq_data *bfqd)
6350	{
6351	u64 now_ns;
6352	u32 delta_us;
6353
6354	bfq_update_hw_tag(bfqd);
6355
6356	bfqd->rq_in_driver[bfqq->actuator_idx]--;
6357	bfqd->tot_rq_in_driver--;
6358	bfqq->dispatched--;
6359
6360	if (!bfqq->dispatched && !bfq_bfqq_busy(bfqq)) {
6361	/*
6362	* Set budget_timeout (which we overload to store the
6363	* time at which the queue remains with no backlog and
6364	* no outstanding request; used by the weight-raising
6365	* mechanism).
6366	*/
6367	bfqq->budget_timeout = jiffies;
6368
6369	bfq_del_bfqq_in_groups_with_pending_reqs(bfqq);
6370	bfq_weights_tree_remove(bfqq);
6371	}
6372
6373	now_ns = blk_time_get_ns();
6374
6375	bfqq->ttime.last_end_request = now_ns;
6376
6377	/*
6378	* Using us instead of ns, to get a reasonable precision in
6379	* computing rate in next check.
6380	*/
6381	delta_us = div_u64(dividend: now_ns - bfqd->last_completion, NSEC_PER_USEC);
6382
6383	/*
6384	* If the request took rather long to complete, and, according
6385	* to the maximum request size recorded, this completion latency
6386	* implies that the request was certainly served at a very low
6387	* rate (less than 1M sectors/sec), then the whole observation
6388	* interval that lasts up to this time instant cannot be a
6389	* valid time interval for computing a new peak rate. Invoke
6390	* bfq_update_rate_reset to have the following three steps
6391	* taken:
6392	* - close the observation interval at the last (previous)
6393	* request dispatch or completion
6394	* - compute rate, if possible, for that observation interval
6395	* - reset to zero samples, which will trigger a proper
6396	* re-initialization of the observation interval on next
6397	* dispatch
6398	*/
6399	if (delta_us > BFQ_MIN_TT/NSEC_PER_USEC &&
6400	(bfqd->last_rq_max_size<<BFQ_RATE_SHIFT)/delta_us <
6401	1UL<<(BFQ_RATE_SHIFT - 10))
6402	bfq_update_rate_reset(bfqd, NULL);
6403	bfqd->last_completion = now_ns;
6404	/*
6405	* Shared queues are likely to receive I/O at a high
6406	* rate. This may deceptively let them be considered as wakers
6407	* of other queues. But a false waker will unjustly steal
6408	* bandwidth to its supposedly woken queue. So considering
6409	* also shared queues in the waking mechanism may cause more
6410	* control troubles than throughput benefits. Then reset
6411	* last_completed_rq_bfqq if bfqq is a shared queue.
6412	*/
6413	if (!bfq_bfqq_coop(bfqq))
6414	bfqd->last_completed_rq_bfqq = bfqq;
6415	else
6416	bfqd->last_completed_rq_bfqq = NULL;
6417
6418	/*
6419	* If we are waiting to discover whether the request pattern
6420	* of the task associated with the queue is actually
6421	* isochronous, and both requisites for this condition to hold
6422	* are now satisfied, then compute soft_rt_next_start (see the
6423	* comments on the function bfq_bfqq_softrt_next_start()). We
6424	* do not compute soft_rt_next_start if bfqq is in interactive
6425	* weight raising (see the comments in bfq_bfqq_expire() for
6426	* an explanation). We schedule this delayed update when bfqq
6427	* expires, if it still has in-flight requests.
6428	*/
6429	if (bfq_bfqq_softrt_update(bfqq) && bfqq->dispatched == 0 &&
6430	RB_EMPTY_ROOT(&bfqq->sort_list) &&
6431	bfqq->wr_coeff != bfqd->bfq_wr_coeff)
6432	bfqq->soft_rt_next_start =
6433	bfq_bfqq_softrt_next_start(bfqd, bfqq);
6434
6435	/*
6436	* If this is the in-service queue, check if it needs to be expired,
6437	* or if we want to idle in case it has no pending requests.
6438	*/
6439	if (bfqd->in_service_queue == bfqq) {
6440	if (bfq_bfqq_must_idle(bfqq)) {
6441	if (bfqq->dispatched == 0)
6442	bfq_arm_slice_timer(bfqd);
6443	/*
6444	* If we get here, we do not expire bfqq, even
6445	* if bfqq was in budget timeout or had no
6446	* more requests (as controlled in the next
6447	* conditional instructions). The reason for
6448	* not expiring bfqq is as follows.
6449	*
6450	* Here bfqq->dispatched > 0 holds, but
6451	* bfq_bfqq_must_idle() returned true. This
6452	* implies that, even if no request arrives
6453	* for bfqq before bfqq->dispatched reaches 0,
6454	* bfqq will, however, not be expired on the
6455	* completion event that causes bfqq->dispatch
6456	* to reach zero. In contrast, on this event,
6457	* bfqq will start enjoying device idling
6458	* (I/O-dispatch plugging).
6459	*
6460	* But, if we expired bfqq here, bfqq would
6461	* not have the chance to enjoy device idling
6462	* when bfqq->dispatched finally reaches
6463	* zero. This would expose bfqq to violation
6464	* of its reserved service guarantees.
6465	*/
6466	return;
6467	} else if (bfq_may_expire_for_budg_timeout(bfqq))
6468	bfq_bfqq_expire(bfqd, bfqq, compensate: false,
6469	reason: BFQQE_BUDGET_TIMEOUT);
6470	else if (RB_EMPTY_ROOT(&bfqq->sort_list) &&
6471	(bfqq->dispatched == 0 ||
6472	!bfq_better_to_idle(bfqq)))
6473	bfq_bfqq_expire(bfqd, bfqq, compensate: false,
6474	reason: BFQQE_NO_MORE_REQUESTS);
6475	}
6476
6477	if (!bfqd->tot_rq_in_driver)
6478	bfq_schedule_dispatch(bfqd);
6479	}
6480
6481	/*
6482	* The processes associated with bfqq may happen to generate their
6483	* cumulative I/O at a lower rate than the rate at which the device
6484	* could serve the same I/O. This is rather probable, e.g., if only
6485	* one process is associated with bfqq and the device is an SSD. It
6486	* results in bfqq becoming often empty while in service. In this
6487	* respect, if BFQ is allowed to switch to another queue when bfqq
6488	* remains empty, then the device goes on being fed with I/O requests,
6489	* and the throughput is not affected. In contrast, if BFQ is not
6490	* allowed to switch to another queue---because bfqq is sync and
6491	* I/O-dispatch needs to be plugged while bfqq is temporarily
6492	* empty---then, during the service of bfqq, there will be frequent
6493	* "service holes", i.e., time intervals during which bfqq gets empty
6494	* and the device can only consume the I/O already queued in its
6495	* hardware queues. During service holes, the device may even get to
6496	* remaining idle. In the end, during the service of bfqq, the device
6497	* is driven at a lower speed than the one it can reach with the kind
6498	* of I/O flowing through bfqq.
6499	*
6500	* To counter this loss of throughput, BFQ implements a "request
6501	* injection mechanism", which tries to fill the above service holes
6502	* with I/O requests taken from other queues. The hard part in this
6503	* mechanism is finding the right amount of I/O to inject, so as to
6504	* both boost throughput and not break bfqq's bandwidth and latency
6505	* guarantees. In this respect, the mechanism maintains a per-queue
6506	* inject limit, computed as below. While bfqq is empty, the injection
6507	* mechanism dispatches extra I/O requests only until the total number
6508	* of I/O requests in flight---i.e., already dispatched but not yet
6509	* completed---remains lower than this limit.
6510	*
6511	* A first definition comes in handy to introduce the algorithm by
6512	* which the inject limit is computed. We define as first request for
6513	* bfqq, an I/O request for bfqq that arrives while bfqq is in
6514	* service, and causes bfqq to switch from empty to non-empty. The
6515	* algorithm updates the limit as a function of the effect of
6516	* injection on the service times of only the first requests of
6517	* bfqq. The reason for this restriction is that these are the
6518	* requests whose service time is affected most, because they are the
6519	* first to arrive after injection possibly occurred.
6520	*
6521	* To evaluate the effect of injection, the algorithm measures the
6522	* "total service time" of first requests. We define as total service
6523	* time of an I/O request, the time that elapses since when the
6524	* request is enqueued into bfqq, to when it is completed. This
6525	* quantity allows the whole effect of injection to be measured. It is
6526	* easy to see why. Suppose that some requests of other queues are
6527	* actually injected while bfqq is empty, and that a new request R
6528	* then arrives for bfqq. If the device does start to serve all or
6529	* part of the injected requests during the service hole, then,
6530	* because of this extra service, it may delay the next invocation of
6531	* the dispatch hook of BFQ. Then, even after R gets eventually
6532	* dispatched, the device may delay the actual service of R if it is
6533	* still busy serving the extra requests, or if it decides to serve,
6534	* before R, some extra request still present in its queues. As a
6535	* conclusion, the cumulative extra delay caused by injection can be
6536	* easily evaluated by just comparing the total service time of first
6537	* requests with and without injection.
6538	*
6539	* The limit-update algorithm works as follows. On the arrival of a
6540	* first request of bfqq, the algorithm measures the total time of the
6541	* request only if one of the three cases below holds, and, for each
6542	* case, it updates the limit as described below:
6543	*
6544	* (1) If there is no in-flight request. This gives a baseline for the
6545	* total service time of the requests of bfqq. If the baseline has
6546	* not been computed yet, then, after computing it, the limit is
6547	* set to 1, to start boosting throughput, and to prepare the
6548	* ground for the next case. If the baseline has already been
6549	* computed, then it is updated, in case it results to be lower
6550	* than the previous value.
6551	*
6552	* (2) If the limit is higher than 0 and there are in-flight
6553	* requests. By comparing the total service time in this case with
6554	* the above baseline, it is possible to know at which extent the
6555	* current value of the limit is inflating the total service
6556	* time. If the inflation is below a certain threshold, then bfqq
6557	* is assumed to be suffering from no perceivable loss of its
6558	* service guarantees, and the limit is even tentatively
6559	* increased. If the inflation is above the threshold, then the
6560	* limit is decreased. Due to the lack of any hysteresis, this
6561	* logic makes the limit oscillate even in steady workload
6562	* conditions. Yet we opted for it, because it is fast in reaching
6563	* the best value for the limit, as a function of the current I/O
6564	* workload. To reduce oscillations, this step is disabled for a
6565	* short time interval after the limit happens to be decreased.
6566	*
6567	* (3) Periodically, after resetting the limit, to make sure that the
6568	* limit eventually drops in case the workload changes. This is
6569	* needed because, after the limit has gone safely up for a
6570	* certain workload, it is impossible to guess whether the
6571	* baseline total service time may have changed, without measuring
6572	* it again without injection. A more effective version of this
6573	* step might be to just sample the baseline, by interrupting
6574	* injection only once, and then to reset/lower the limit only if
6575	* the total service time with the current limit does happen to be
6576	* too large.
6577	*
6578	* More details on each step are provided in the comments on the
6579	* pieces of code that implement these steps: the branch handling the
6580	* transition from empty to non empty in bfq_add_request(), the branch
6581	* handling injection in bfq_select_queue(), and the function
6582	* bfq_choose_bfqq_for_injection(). These comments also explain some
6583	* exceptions, made by the injection mechanism in some special cases.
6584	*/
6585	static void bfq_update_inject_limit(struct bfq_data *bfqd,
6586	struct bfq_queue *bfqq)
6587	{
6588	u64 tot_time_ns = blk_time_get_ns() - bfqd->last_empty_occupied_ns;
6589	unsigned int old_limit = bfqq->inject_limit;
6590
6591	if (bfqq->last_serv_time_ns > 0 && bfqd->rqs_injected) {
6592	u64 threshold = (bfqq->last_serv_time_ns * 3)>>1;
6593
6594	if (tot_time_ns >= threshold && old_limit > 0) {
6595	bfqq->inject_limit--;
6596	bfqq->decrease_time_jif = jiffies;
6597	} else if (tot_time_ns < threshold &&
6598	old_limit <= bfqd->max_rq_in_driver)
6599	bfqq->inject_limit++;
6600	}
6601
6602	/*
6603	* Either we still have to compute the base value for the
6604	* total service time, and there seem to be the right
6605	* conditions to do it, or we can lower the last base value
6606	* computed.
6607	*
6608	* NOTE: (bfqd->tot_rq_in_driver == 1) means that there is no I/O
6609	* request in flight, because this function is in the code
6610	* path that handles the completion of a request of bfqq, and,
6611	* in particular, this function is executed before
6612	* bfqd->tot_rq_in_driver is decremented in such a code path.
6613	*/
6614	if ((bfqq->last_serv_time_ns == 0 && bfqd->tot_rq_in_driver == 1) ||
6615	tot_time_ns < bfqq->last_serv_time_ns) {
6616	if (bfqq->last_serv_time_ns == 0) {
6617	/*
6618	* Now we certainly have a base value: make sure we
6619	* start trying injection.
6620	*/
6621	bfqq->inject_limit = max_t(unsigned int, 1, old_limit);
6622	}
6623	bfqq->last_serv_time_ns = tot_time_ns;
6624	} else if (!bfqd->rqs_injected && bfqd->tot_rq_in_driver == 1)
6625	/*
6626	* No I/O injected and no request still in service in
6627	* the drive: these are the exact conditions for
6628	* computing the base value of the total service time
6629	* for bfqq. So let's update this value, because it is
6630	* rather variable. For example, it varies if the size
6631	* or the spatial locality of the I/O requests in bfqq
6632	* change.
6633	*/
6634	bfqq->last_serv_time_ns = tot_time_ns;
6635
6636
6637	/* update complete, not waiting for any request completion any longer */
6638	bfqd->waited_rq = NULL;
6639	bfqd->rqs_injected = false;
6640	}
6641
6642	/*
6643	* Handle either a requeue or a finish for rq. The things to do are
6644	* the same in both cases: all references to rq are to be dropped. In
6645	* particular, rq is considered completed from the point of view of
6646	* the scheduler.
6647	*/
6648	static void bfq_finish_requeue_request(struct request *rq)
6649	{
6650	struct bfq_queue *bfqq = RQ_BFQQ(rq);
6651	struct bfq_data *bfqd;
6652	unsigned long flags;
6653
6654	/*
6655	* rq either is not associated with any icq, or is an already
6656	* requeued request that has not (yet) been re-inserted into
6657	* a bfq_queue.
6658	*/
6659	if (!rq->elv.icq || !bfqq)
6660	return;
6661
6662	bfqd = bfqq->bfqd;
6663
6664	if (rq->rq_flags & RQF_STARTED)
6665	bfqg_stats_update_completion(bfqg: bfqq_group(bfqq),
6666	start_time_ns: rq->start_time_ns,
6667	io_start_time_ns: rq->io_start_time_ns,
6668	opf: rq->cmd_flags);
6669
6670	spin_lock_irqsave(&bfqd->lock, flags);
6671	if (likely(rq->rq_flags & RQF_STARTED)) {
6672	if (rq == bfqd->waited_rq)
6673	bfq_update_inject_limit(bfqd, bfqq);
6674
6675	bfq_completed_request(bfqq, bfqd);
6676	}
6677	bfqq_request_freed(bfqq);
6678	bfq_put_queue(bfqq);
6679	RQ_BIC(rq)->requests--;
6680	spin_unlock_irqrestore(lock: &bfqd->lock, flags);
6681
6682	/*
6683	* Reset private fields. In case of a requeue, this allows
6684	* this function to correctly do nothing if it is spuriously
6685	* invoked again on this same request (see the check at the
6686	* beginning of the function). Probably, a better general
6687	* design would be to prevent blk-mq from invoking the requeue
6688	* or finish hooks of an elevator, for a request that is not
6689	* referred by that elevator.
6690	*
6691	* Resetting the following fields would break the
6692	* request-insertion logic if rq is re-inserted into a bfq
6693	* internal queue, without a re-preparation. Here we assume
6694	* that re-insertions of requeued requests, without
6695	* re-preparation, can happen only for pass_through or at_head
6696	* requests (which are not re-inserted into bfq internal
6697	* queues).
6698	*/
6699	rq->elv.priv[0] = NULL;
6700	rq->elv.priv[1] = NULL;
6701	}
6702
6703	static void bfq_finish_request(struct request *rq)
6704	{
6705	bfq_finish_requeue_request(rq);
6706
6707	if (rq->elv.icq) {
6708	put_io_context(ioc: rq->elv.icq->ioc);
6709	rq->elv.icq = NULL;
6710	}
6711	}
6712
6713	/*
6714	* Removes the association between the current task and bfqq, assuming
6715	* that bic points to the bfq iocontext of the task.
6716	* Returns NULL if a new bfqq should be allocated, or the old bfqq if this
6717	* was the last process referring to that bfqq.
6718	*/
6719	static struct bfq_queue *
6720	bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
6721	{
6722	bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue");
6723
6724	if (bfqq_process_refs(bfqq) == 1) {
6725	bfqq->pid = current->pid;
6726	bfq_clear_bfqq_coop(bfqq);
6727	bfq_clear_bfqq_split_coop(bfqq);
6728	return bfqq;
6729	}
6730
6731	bic_set_bfqq(bic, NULL, is_sync: true, actuator_idx: bfqq->actuator_idx);
6732
6733	bfq_put_cooperator(bfqq);
6734
6735	bfq_release_process_ref(bfqd: bfqq->bfqd, bfqq);
6736	return NULL;
6737	}
6738
6739	static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
6740	struct bfq_io_cq *bic,
6741	struct bio *bio,
6742	bool split, bool is_sync,
6743	bool *new_queue)
6744	{
6745	unsigned int act_idx = bfq_actuator_index(bfqd, bio);
6746	struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, actuator_idx: act_idx);
6747	struct bfq_iocq_bfqq_data *bfqq_data = &bic->bfqq_data[act_idx];
6748
6749	if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
6750	return bfqq;
6751
6752	if (new_queue)
6753	*new_queue = true;
6754
6755	if (bfqq)
6756	bfq_put_queue(bfqq);
6757	bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, respawn: split);
6758
6759	bic_set_bfqq(bic, bfqq, is_sync, actuator_idx: act_idx);
6760	if (split && is_sync) {
6761	if ((bfqq_data->was_in_burst_list && bfqd->large_burst) ||
6762	bfqq_data->saved_in_large_burst)
6763	bfq_mark_bfqq_in_large_burst(bfqq);
6764	else {
6765	bfq_clear_bfqq_in_large_burst(bfqq);
6766	if (bfqq_data->was_in_burst_list)
6767	/*
6768	* If bfqq was in the current
6769	* burst list before being
6770	* merged, then we have to add
6771	* it back. And we do not need
6772	* to increase burst_size, as
6773	* we did not decrement
6774	* burst_size when we removed
6775	* bfqq from the burst list as
6776	* a consequence of a merge
6777	* (see comments in
6778	* bfq_put_queue). In this
6779	* respect, it would be rather
6780	* costly to know whether the
6781	* current burst list is still
6782	* the same burst list from
6783	* which bfqq was removed on
6784	* the merge. To avoid this
6785	* cost, if bfqq was in a
6786	* burst list, then we add
6787	* bfqq to the current burst
6788	* list without any further
6789	* check. This can cause
6790	* inappropriate insertions,
6791	* but rarely enough to not
6792	* harm the detection of large
6793	* bursts significantly.
6794	*/
6795	hlist_add_head(n: &bfqq->burst_list_node,
6796	h: &bfqd->burst_list);
6797	}
6798	bfqq->split_time = jiffies;
6799	}
6800
6801	return bfqq;
6802	}
6803
6804	/*
6805	* Only reset private fields. The actual request preparation will be
6806	* performed by bfq_init_rq, when rq is either inserted or merged. See
6807	* comments on bfq_init_rq for the reason behind this delayed
6808	* preparation.
6809	*/
6810	static void bfq_prepare_request(struct request *rq)
6811	{
6812	rq->elv.icq = ioc_find_get_icq(q: rq->q);
6813
6814	/*
6815	* Regardless of whether we have an icq attached, we have to
6816	* clear the scheduler pointers, as they might point to
6817	* previously allocated bic/bfqq structs.
6818	*/
6819	rq->elv.priv[0] = rq->elv.priv[1] = NULL;
6820	}
6821
6822	/*
6823	* If needed, init rq, allocate bfq data structures associated with
6824	* rq, and increment reference counters in the destination bfq_queue
6825	* for rq. Return the destination bfq_queue for rq, or NULL is rq is
6826	* not associated with any bfq_queue.
6827	*
6828	* This function is invoked by the functions that perform rq insertion
6829	* or merging. One may have expected the above preparation operations
6830	* to be performed in bfq_prepare_request, and not delayed to when rq
6831	* is inserted or merged. The rationale behind this delayed
6832	* preparation is that, after the prepare_request hook is invoked for
6833	* rq, rq may still be transformed into a request with no icq, i.e., a
6834	* request not associated with any queue. No bfq hook is invoked to
6835	* signal this transformation. As a consequence, should these
6836	* preparation operations be performed when the prepare_request hook
6837	* is invoked, and should rq be transformed one moment later, bfq
6838	* would end up in an inconsistent state, because it would have
6839	* incremented some queue counters for an rq destined to
6840	* transformation, without any chance to correctly lower these
6841	* counters back. In contrast, no transformation can still happen for
6842	* rq after rq has been inserted or merged. So, it is safe to execute
6843	* these preparation operations when rq is finally inserted or merged.
6844	*/
6845	static struct bfq_queue *bfq_init_rq(struct request *rq)
6846	{
6847	struct request_queue *q = rq->q;
6848	struct bio *bio = rq->bio;
6849	struct bfq_data *bfqd = q->elevator->elevator_data;
6850	struct bfq_io_cq *bic;
6851	const int is_sync = rq_is_sync(rq);
6852	struct bfq_queue *bfqq;
6853	bool new_queue = false;
6854	bool bfqq_already_existing = false, split = false;
6855	unsigned int a_idx = bfq_actuator_index(bfqd, bio);
6856
6857	if (unlikely(!rq->elv.icq))
6858	return NULL;
6859
6860	/*
6861	* Assuming that RQ_BFQQ(rq) is set only if everything is set
6862	* for this rq. This holds true, because this function is
6863	* invoked only for insertion or merging, and, after such
6864	* events, a request cannot be manipulated any longer before
6865	* being removed from bfq.
6866	*/
6867	if (RQ_BFQQ(rq))
6868	return RQ_BFQQ(rq);
6869
6870	bic = icq_to_bic(icq: rq->elv.icq);
6871
6872	bfq_check_ioprio_change(bic, bio);
6873
6874	bfq_bic_update_cgroup(bic, bio);
6875
6876	bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio, split: false, is_sync,
6877	new_queue: &new_queue);
6878
6879	if (likely(!new_queue)) {
6880	/* If the queue was seeky for too long, break it apart. */
6881	if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
6882	!bic->bfqq_data[a_idx].stably_merged) {
6883	struct bfq_queue *old_bfqq = bfqq;
6884
6885	/* Update bic before losing reference to bfqq */
6886	if (bfq_bfqq_in_large_burst(bfqq))
6887	bic->bfqq_data[a_idx].saved_in_large_burst =
6888	true;
6889
6890	bfqq = bfq_split_bfqq(bic, bfqq);
6891	split = true;
6892
6893	if (!bfqq) {
6894	bfqq = bfq_get_bfqq_handle_split(bfqd, bic, bio,
6895	split: true, is_sync,
6896	NULL);
6897	if (unlikely(bfqq == &bfqd->oom_bfqq))
6898	bfqq_already_existing = true;
6899	} else
6900	bfqq_already_existing = true;
6901
6902	if (!bfqq_already_existing) {
6903	bfqq->waker_bfqq = old_bfqq->waker_bfqq;
6904	bfqq->tentative_waker_bfqq = NULL;
6905
6906	/*
6907	* If the waker queue disappears, then
6908	* new_bfqq->waker_bfqq must be
6909	* reset. So insert new_bfqq into the
6910	* woken_list of the waker. See
6911	* bfq_check_waker for details.
6912	*/
6913	if (bfqq->waker_bfqq)
6914	hlist_add_head(n: &bfqq->woken_list_node,
6915	h: &bfqq->waker_bfqq->woken_list);
6916	}
6917	}
6918	}
6919
6920	bfqq_request_allocated(bfqq);
6921	bfqq->ref++;
6922	bic->requests++;
6923	bfq_log_bfqq(bfqd, bfqq, "get_request %p: bfqq %p, %d",
6924	rq, bfqq, bfqq->ref);
6925
6926	rq->elv.priv[0] = bic;
6927	rq->elv.priv[1] = bfqq;
6928
6929	/*
6930	* If a bfq_queue has only one process reference, it is owned
6931	* by only this bic: we can then set bfqq->bic = bic. in
6932	* addition, if the queue has also just been split, we have to
6933	* resume its state.
6934	*/
6935	if (likely(bfqq != &bfqd->oom_bfqq) && bfqq_process_refs(bfqq) == 1) {
6936	bfqq->bic = bic;
6937	if (split) {
6938	/*
6939	* The queue has just been split from a shared
6940	* queue: restore the idle window and the
6941	* possible weight raising period.
6942	*/
6943	bfq_bfqq_resume_state(bfqq, bfqd, bic,
6944	bfq_already_existing: bfqq_already_existing);
6945	}
6946	}
6947
6948	/*
6949	* Consider bfqq as possibly belonging to a burst of newly
6950	* created queues only if:
6951	* 1) A burst is actually happening (bfqd->burst_size > 0)
6952	* or
6953	* 2) There is no other active queue. In fact, if, in
6954	* contrast, there are active queues not belonging to the
6955	* possible burst bfqq may belong to, then there is no gain
6956	* in considering bfqq as belonging to a burst, and
6957	* therefore in not weight-raising bfqq. See comments on
6958	* bfq_handle_burst().
6959	*
6960	* This filtering also helps eliminating false positives,
6961	* occurring when bfqq does not belong to an actual large
6962	* burst, but some background task (e.g., a service) happens
6963	* to trigger the creation of new queues very close to when
6964	* bfqq and its possible companion queues are created. See
6965	* comments on bfq_handle_burst() for further details also on
6966	* this issue.
6967	*/
6968	if (unlikely(bfq_bfqq_just_created(bfqq) &&
6969	(bfqd->burst_size > 0 ||
6970	bfq_tot_busy_queues(bfqd) == 0)))
6971	bfq_handle_burst(bfqd, bfqq);
6972
6973	return bfqq;
6974	}
6975
6976	static void
6977	bfq_idle_slice_timer_body(struct bfq_data *bfqd, struct bfq_queue *bfqq)
6978	{
6979	enum bfqq_expiration reason;
6980	unsigned long flags;
6981
6982	spin_lock_irqsave(&bfqd->lock, flags);
6983
6984	/*
6985	* Considering that bfqq may be in race, we should firstly check
6986	* whether bfqq is in service before doing something on it. If
6987	* the bfqq in race is not in service, it has already been expired
6988	* through __bfq_bfqq_expire func and its wait_request flags has
6989	* been cleared in __bfq_bfqd_reset_in_service func.
6990	*/
6991	if (bfqq != bfqd->in_service_queue) {
6992	spin_unlock_irqrestore(lock: &bfqd->lock, flags);
6993	return;
6994	}
6995
6996	bfq_clear_bfqq_wait_request(bfqq);
6997
6998	if (bfq_bfqq_budget_timeout(bfqq))
6999	/*
7000	* Also here the queue can be safely expired
7001	* for budget timeout without wasting
7002	* guarantees
7003	*/
7004	reason = BFQQE_BUDGET_TIMEOUT;
7005	else if (bfqq->queued[0] == 0 && bfqq->queued[1] == 0)
7006	/*
7007	* The queue may not be empty upon timer expiration,
7008	* because we may not disable the timer when the
7009	* first request of the in-service queue arrives
7010	* during disk idling.
7011	*/
7012	reason = BFQQE_TOO_IDLE;
7013	else
7014	goto schedule_dispatch;
7015
7016	bfq_bfqq_expire(bfqd, bfqq, compensate: true, reason);
7017
7018	schedule_dispatch:
7019	bfq_schedule_dispatch(bfqd);
7020	spin_unlock_irqrestore(lock: &bfqd->lock, flags);
7021	}
7022
7023	/*
7024	* Handler of the expiration of the timer running if the in-service queue
7025	* is idling inside its time slice.
7026	*/
7027	static enum hrtimer_restart bfq_idle_slice_timer(struct hrtimer *timer)
7028	{
7029	struct bfq_data *bfqd = container_of(timer, struct bfq_data,
7030	idle_slice_timer);
7031	struct bfq_queue *bfqq = bfqd->in_service_queue;
7032
7033	/*
7034	* Theoretical race here: the in-service queue can be NULL or
7035	* different from the queue that was idling if a new request
7036	* arrives for the current queue and there is a full dispatch
7037	* cycle that changes the in-service queue. This can hardly
7038	* happen, but in the worst case we just expire a queue too
7039	* early.
7040	*/
7041	if (bfqq)
7042	bfq_idle_slice_timer_body(bfqd, bfqq);
7043
7044	return HRTIMER_NORESTART;
7045	}
7046
7047	static void __bfq_put_async_bfqq(struct bfq_data *bfqd,
7048	struct bfq_queue **bfqq_ptr)
7049	{
7050	struct bfq_queue *bfqq = *bfqq_ptr;
7051
7052	bfq_log(bfqd, "put_async_bfqq: %p", bfqq);
7053	if (bfqq) {
7054	bfq_bfqq_move(bfqd, bfqq, bfqg: bfqd->root_group);
7055
7056	bfq_log_bfqq(bfqd, bfqq, "put_async_bfqq: putting %p, %d",
7057	bfqq, bfqq->ref);
7058	bfq_put_queue(bfqq);
7059	*bfqq_ptr = NULL;
7060	}
7061	}
7062
7063	/*
7064	* Release all the bfqg references to its async queues. If we are
7065	* deallocating the group these queues may still contain requests, so
7066	* we reparent them to the root cgroup (i.e., the only one that will
7067	* exist for sure until all the requests on a device are gone).
7068	*/
7069	void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
7070	{
7071	int i, j, k;
7072
7073	for (k = 0; k < bfqd->num_actuators; k++) {
7074	for (i = 0; i < 2; i++)
7075	for (j = 0; j < IOPRIO_NR_LEVELS; j++)
7076	__bfq_put_async_bfqq(bfqd, bfqq_ptr: &bfqg->async_bfqq[i][j][k]);
7077
7078	__bfq_put_async_bfqq(bfqd, bfqq_ptr: &bfqg->async_idle_bfqq[k]);
7079	}
7080	}
7081
7082	/*
7083	* See the comments on bfq_limit_depth for the purpose of
7084	* the depths set in the function. Return minimum shallow depth we'll use.
7085	*/
7086	static void bfq_update_depths(struct bfq_data *bfqd, struct sbitmap_queue *bt)
7087	{
7088	unsigned int depth = 1U << bt->sb.shift;
7089
7090	bfqd->full_depth_shift = bt->sb.shift;
7091	/*
7092	* In-word depths if no bfq_queue is being weight-raised:
7093	* leaving 25% of tags only for sync reads.
7094	*
7095	* In next formulas, right-shift the value
7096	* (1U<<bt->sb.shift), instead of computing directly
7097	* (1U<<(bt->sb.shift - something)), to be robust against
7098	* any possible value of bt->sb.shift, without having to
7099	* limit 'something'.
7100	*/
7101	/* no more than 50% of tags for async I/O */
7102	bfqd->word_depths[0][0] = max(depth >> 1, 1U);
7103	/*
7104	* no more than 75% of tags for sync writes (25% extra tags
7105	* w.r.t. async I/O, to prevent async I/O from starving sync
7106	* writes)
7107	*/
7108	bfqd->word_depths[0][1] = max((depth * 3) >> 2, 1U);
7109
7110	/*
7111	* In-word depths in case some bfq_queue is being weight-
7112	* raised: leaving ~63% of tags for sync reads. This is the
7113	* highest percentage for which, in our tests, application
7114	* start-up times didn't suffer from any regression due to tag
7115	* shortage.
7116	*/
7117	/* no more than ~18% of tags for async I/O */
7118	bfqd->word_depths[1][0] = max((depth * 3) >> 4, 1U);
7119	/* no more than ~37% of tags for sync writes (~20% extra tags) */
7120	bfqd->word_depths[1][1] = max((depth * 6) >> 4, 1U);
7121	}
7122
7123	static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
7124	{
7125	struct bfq_data *bfqd = hctx->queue->elevator->elevator_data;
7126	struct blk_mq_tags *tags = hctx->sched_tags;
7127
7128	bfq_update_depths(bfqd, bt: &tags->bitmap_tags);
7129	sbitmap_queue_min_shallow_depth(sbq: &tags->bitmap_tags, min_shallow_depth: 1);
7130	}
7131
7132	static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
7133	{
7134	bfq_depth_updated(hctx);
7135	return 0;
7136	}
7137
7138	static void bfq_exit_queue(struct elevator_queue *e)
7139	{
7140	struct bfq_data *bfqd = e->elevator_data;
7141	struct bfq_queue *bfqq, *n;
7142	unsigned int actuator;
7143
7144	hrtimer_cancel(timer: &bfqd->idle_slice_timer);
7145
7146	spin_lock_irq(lock: &bfqd->lock);
7147	list_for_each_entry_safe(bfqq, n, &bfqd->idle_list, bfqq_list)
7148	bfq_deactivate_bfqq(bfqd, bfqq, ins_into_idle_tree: false, expiration: false);
7149	spin_unlock_irq(lock: &bfqd->lock);
7150
7151	for (actuator = 0; actuator < bfqd->num_actuators; actuator++)
7152	WARN_ON_ONCE(bfqd->rq_in_driver[actuator]);
7153	WARN_ON_ONCE(bfqd->tot_rq_in_driver);
7154
7155	hrtimer_cancel(timer: &bfqd->idle_slice_timer);
7156
7157	/* release oom-queue reference to root group */
7158	bfqg_and_blkg_put(bfqg: bfqd->root_group);
7159
7160	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7161	blkcg_deactivate_policy(disk: bfqd->queue->disk, pol: &blkcg_policy_bfq);
7162	#else
7163	spin_lock_irq(&bfqd->lock);
7164	bfq_put_async_queues(bfqd, bfqd->root_group);
7165	kfree(bfqd->root_group);
7166	spin_unlock_irq(&bfqd->lock);
7167	#endif
7168
7169	blk_stat_disable_accounting(q: bfqd->queue);
7170	clear_bit(ELEVATOR_FLAG_DISABLE_WBT, addr: &e->flags);
7171	wbt_enable_default(disk: bfqd->queue->disk);
7172
7173	kfree(objp: bfqd);
7174	}
7175
7176	static void bfq_init_root_group(struct bfq_group *root_group,
7177	struct bfq_data *bfqd)
7178	{
7179	int i;
7180
7181	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7182	root_group->entity.parent = NULL;
7183	root_group->my_entity = NULL;
7184	root_group->bfqd = bfqd;
7185	#endif
7186	root_group->rq_pos_tree = RB_ROOT;
7187	for (i = 0; i < BFQ_IOPRIO_CLASSES; i++)
7188	root_group->sched_data.service_tree[i] = BFQ_SERVICE_TREE_INIT;
7189	root_group->sched_data.bfq_class_idle_last_service = jiffies;
7190	}
7191
7192	static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
7193	{
7194	struct bfq_data *bfqd;
7195	struct elevator_queue *eq;
7196	unsigned int i;
7197	struct blk_independent_access_ranges *ia_ranges = q->disk->ia_ranges;
7198
7199	eq = elevator_alloc(q, e);
7200	if (!eq)
7201	return -ENOMEM;
7202
7203	bfqd = kzalloc_node(size: sizeof(*bfqd), GFP_KERNEL, node: q->node);
7204	if (!bfqd) {
7205	kobject_put(kobj: &eq->kobj);
7206	return -ENOMEM;
7207	}
7208	eq->elevator_data = bfqd;
7209
7210	spin_lock_irq(lock: &q->queue_lock);
7211	q->elevator = eq;
7212	spin_unlock_irq(lock: &q->queue_lock);
7213
7214	/*
7215	* Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
7216	* Grab a permanent reference to it, so that the normal code flow
7217	* will not attempt to free it.
7218	* Set zero as actuator index: we will pretend that
7219	* all I/O requests are for the same actuator.
7220	*/
7221	bfq_init_bfqq(bfqd, bfqq: &bfqd->oom_bfqq, NULL, pid: 1, is_sync: 0, act_idx: 0);
7222	bfqd->oom_bfqq.ref++;
7223	bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
7224	bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
7225	bfqd->oom_bfqq.entity.new_weight =
7226	bfq_ioprio_to_weight(ioprio: bfqd->oom_bfqq.new_ioprio);
7227
7228	/* oom_bfqq does not participate to bursts */
7229	bfq_clear_bfqq_just_created(bfqq: &bfqd->oom_bfqq);
7230
7231	/*
7232	* Trigger weight initialization, according to ioprio, at the
7233	* oom_bfqq's first activation. The oom_bfqq's ioprio and ioprio
7234	* class won't be changed any more.
7235	*/
7236	bfqd->oom_bfqq.entity.prio_changed = 1;
7237
7238	bfqd->queue = q;
7239
7240	bfqd->num_actuators = 1;
7241	/*
7242	* If the disk supports multiple actuators, copy independent
7243	* access ranges from the request queue structure.
7244	*/
7245	spin_lock_irq(lock: &q->queue_lock);
7246	if (ia_ranges) {
7247	/*
7248	* Check if the disk ia_ranges size exceeds the current bfq
7249	* actuator limit.
7250	*/
7251	if (ia_ranges->nr_ia_ranges > BFQ_MAX_ACTUATORS) {
7252	pr_crit("nr_ia_ranges higher than act limit: iars=%d, max=%d.\n",
7253	ia_ranges->nr_ia_ranges, BFQ_MAX_ACTUATORS);
7254	pr_crit("Falling back to single actuator mode.\n");
7255	} else {
7256	bfqd->num_actuators = ia_ranges->nr_ia_ranges;
7257
7258	for (i = 0; i < bfqd->num_actuators; i++) {
7259	bfqd->sector[i] = ia_ranges->ia_range[i].sector;
7260	bfqd->nr_sectors[i] =
7261	ia_ranges->ia_range[i].nr_sectors;
7262	}
7263	}
7264	}
7265
7266	/* Otherwise use single-actuator dev info */
7267	if (bfqd->num_actuators == 1) {
7268	bfqd->sector[0] = 0;
7269	bfqd->nr_sectors[0] = get_capacity(disk: q->disk);
7270	}
7271	spin_unlock_irq(lock: &q->queue_lock);
7272
7273	INIT_LIST_HEAD(list: &bfqd->dispatch);
7274
7275	hrtimer_init(timer: &bfqd->idle_slice_timer, CLOCK_MONOTONIC,
7276	mode: HRTIMER_MODE_REL);
7277	bfqd->idle_slice_timer.function = bfq_idle_slice_timer;
7278
7279	bfqd->queue_weights_tree = RB_ROOT_CACHED;
7280	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7281	bfqd->num_groups_with_pending_reqs = 0;
7282	#endif
7283
7284	INIT_LIST_HEAD(list: &bfqd->active_list[0]);
7285	INIT_LIST_HEAD(list: &bfqd->active_list[1]);
7286	INIT_LIST_HEAD(list: &bfqd->idle_list);
7287	INIT_HLIST_HEAD(&bfqd->burst_list);
7288
7289	bfqd->hw_tag = -1;
7290	bfqd->nonrot_with_queueing = blk_queue_nonrot(bfqd->queue);
7291
7292	bfqd->bfq_max_budget = bfq_default_max_budget;
7293
7294	bfqd->bfq_fifo_expire[0] = bfq_fifo_expire[0];
7295	bfqd->bfq_fifo_expire[1] = bfq_fifo_expire[1];
7296	bfqd->bfq_back_max = bfq_back_max;
7297	bfqd->bfq_back_penalty = bfq_back_penalty;
7298	bfqd->bfq_slice_idle = bfq_slice_idle;
7299	bfqd->bfq_timeout = bfq_timeout;
7300
7301	bfqd->bfq_large_burst_thresh = 8;
7302	bfqd->bfq_burst_interval = msecs_to_jiffies(m: 180);
7303
7304	bfqd->low_latency = true;
7305
7306	/*
7307	* Trade-off between responsiveness and fairness.
7308	*/
7309	bfqd->bfq_wr_coeff = 30;
7310	bfqd->bfq_wr_rt_max_time = msecs_to_jiffies(m: 300);
7311	bfqd->bfq_wr_min_idle_time = msecs_to_jiffies(m: 2000);
7312	bfqd->bfq_wr_min_inter_arr_async = msecs_to_jiffies(m: 500);
7313	bfqd->bfq_wr_max_softrt_rate = 7000; /*
7314	* Approximate rate required
7315	* to playback or record a
7316	* high-definition compressed
7317	* video.
7318	*/
7319	bfqd->wr_busy_queues = 0;
7320
7321	/*
7322	* Begin by assuming, optimistically, that the device peak
7323	* rate is equal to 2/3 of the highest reference rate.
7324	*/
7325	bfqd->rate_dur_prod = ref_rate[blk_queue_nonrot(bfqd->queue)] *
7326	ref_wr_duration[blk_queue_nonrot(bfqd->queue)];
7327	bfqd->peak_rate = ref_rate[blk_queue_nonrot(bfqd->queue)] * 2 / 3;
7328
7329	/* see comments on the definition of next field inside bfq_data */
7330	bfqd->actuator_load_threshold = 4;
7331
7332	spin_lock_init(&bfqd->lock);
7333
7334	/*
7335	* The invocation of the next bfq_create_group_hierarchy
7336	* function is the head of a chain of function calls
7337	* (bfq_create_group_hierarchy->blkcg_activate_policy->
7338	* blk_mq_freeze_queue) that may lead to the invocation of the
7339	* has_work hook function. For this reason,
7340	* bfq_create_group_hierarchy is invoked only after all
7341	* scheduler data has been initialized, apart from the fields
7342	* that can be initialized only after invoking
7343	* bfq_create_group_hierarchy. This, in particular, enables
7344	* has_work to correctly return false. Of course, to avoid
7345	* other inconsistencies, the blk-mq stack must then refrain
7346	* from invoking further scheduler hooks before this init
7347	* function is finished.
7348	*/
7349	bfqd->root_group = bfq_create_group_hierarchy(bfqd, node: q->node);
7350	if (!bfqd->root_group)
7351	goto out_free;
7352	bfq_init_root_group(root_group: bfqd->root_group, bfqd);
7353	bfq_init_entity(entity: &bfqd->oom_bfqq.entity, bfqg: bfqd->root_group);
7354
7355	/* We dispatch from request queue wide instead of hw queue */
7356	blk_queue_flag_set(QUEUE_FLAG_SQ_SCHED, q);
7357
7358	set_bit(ELEVATOR_FLAG_DISABLE_WBT, addr: &eq->flags);
7359	wbt_disable_default(disk: q->disk);
7360	blk_stat_enable_accounting(q);
7361
7362	return 0;
7363
7364	out_free:
7365	kfree(objp: bfqd);
7366	kobject_put(kobj: &eq->kobj);
7367	return -ENOMEM;
7368	}
7369
7370	static void bfq_slab_kill(void)
7371	{
7372	kmem_cache_destroy(s: bfq_pool);
7373	}
7374
7375	static int __init bfq_slab_setup(void)
7376	{
7377	bfq_pool = KMEM_CACHE(bfq_queue, 0);
7378	if (!bfq_pool)
7379	return -ENOMEM;
7380	return 0;
7381	}
7382
7383	static ssize_t bfq_var_show(unsigned int var, char *page)
7384	{
7385	return sprintf(buf: page, fmt: "%u\n", var);
7386	}
7387
7388	static int bfq_var_store(unsigned long *var, const char *page)
7389	{
7390	unsigned long new_val;
7391	int ret = kstrtoul(s: page, base: 10, res: &new_val);
7392
7393	if (ret)
7394	return ret;
7395	*var = new_val;
7396	return 0;
7397	}
7398
7399	#define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
7400	static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7401	{ \
7402	struct bfq_data *bfqd = e->elevator_data; \
7403	u64 __data = __VAR; \
7404	if (__CONV == 1) \
7405	__data = jiffies_to_msecs(__data); \
7406	else if (__CONV == 2) \
7407	__data = div_u64(__data, NSEC_PER_MSEC); \
7408	return bfq_var_show(__data, (page)); \
7409	}
7410	SHOW_FUNCTION(bfq_fifo_expire_sync_show, bfqd->bfq_fifo_expire[1], 2);
7411	SHOW_FUNCTION(bfq_fifo_expire_async_show, bfqd->bfq_fifo_expire[0], 2);
7412	SHOW_FUNCTION(bfq_back_seek_max_show, bfqd->bfq_back_max, 0);
7413	SHOW_FUNCTION(bfq_back_seek_penalty_show, bfqd->bfq_back_penalty, 0);
7414	SHOW_FUNCTION(bfq_slice_idle_show, bfqd->bfq_slice_idle, 2);
7415	SHOW_FUNCTION(bfq_max_budget_show, bfqd->bfq_user_max_budget, 0);
7416	SHOW_FUNCTION(bfq_timeout_sync_show, bfqd->bfq_timeout, 1);
7417	SHOW_FUNCTION(bfq_strict_guarantees_show, bfqd->strict_guarantees, 0);
7418	SHOW_FUNCTION(bfq_low_latency_show, bfqd->low_latency, 0);
7419	#undef SHOW_FUNCTION
7420
7421	#define USEC_SHOW_FUNCTION(__FUNC, __VAR) \
7422	static ssize_t __FUNC(struct elevator_queue *e, char *page) \
7423	{ \
7424	struct bfq_data *bfqd = e->elevator_data; \
7425	u64 __data = __VAR; \
7426	__data = div_u64(__data, NSEC_PER_USEC); \
7427	return bfq_var_show(__data, (page)); \
7428	}
7429	USEC_SHOW_FUNCTION(bfq_slice_idle_us_show, bfqd->bfq_slice_idle);
7430	#undef USEC_SHOW_FUNCTION
7431
7432	#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
7433	static ssize_t \
7434	__FUNC(struct elevator_queue *e, const char *page, size_t count) \
7435	{ \
7436	struct bfq_data *bfqd = e->elevator_data; \
7437	unsigned long __data, __min = (MIN), __max = (MAX); \
7438	int ret; \
7439	\
7440	ret = bfq_var_store(&__data, (page)); \
7441	if (ret) \
7442	return ret; \
7443	if (__data < __min) \
7444	__data = __min; \
7445	else if (__data > __max) \
7446	__data = __max; \
7447	if (__CONV == 1) \
7448	*(__PTR) = msecs_to_jiffies(__data); \
7449	else if (__CONV == 2) \
7450	*(__PTR) = (u64)__data * NSEC_PER_MSEC; \
7451	else \
7452	*(__PTR) = __data; \
7453	return count; \
7454	}
7455	STORE_FUNCTION(bfq_fifo_expire_sync_store, &bfqd->bfq_fifo_expire[1], 1,
7456	INT_MAX, 2);
7457	STORE_FUNCTION(bfq_fifo_expire_async_store, &bfqd->bfq_fifo_expire[0], 1,
7458	INT_MAX, 2);
7459	STORE_FUNCTION(bfq_back_seek_max_store, &bfqd->bfq_back_max, 0, INT_MAX, 0);
7460	STORE_FUNCTION(bfq_back_seek_penalty_store, &bfqd->bfq_back_penalty, 1,
7461	INT_MAX, 0);
7462	STORE_FUNCTION(bfq_slice_idle_store, &bfqd->bfq_slice_idle, 0, INT_MAX, 2);
7463	#undef STORE_FUNCTION
7464
7465	#define USEC_STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
7466	static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count)\
7467	{ \
7468	struct bfq_data *bfqd = e->elevator_data; \
7469	unsigned long __data, __min = (MIN), __max = (MAX); \
7470	int ret; \
7471	\
7472	ret = bfq_var_store(&__data, (page)); \
7473	if (ret) \
7474	return ret; \
7475	if (__data < __min) \
7476	__data = __min; \
7477	else if (__data > __max) \
7478	__data = __max; \
7479	*(__PTR) = (u64)__data * NSEC_PER_USEC; \
7480	return count; \
7481	}
7482	USEC_STORE_FUNCTION(bfq_slice_idle_us_store, &bfqd->bfq_slice_idle, 0,
7483	UINT_MAX);
7484	#undef USEC_STORE_FUNCTION
7485
7486	static ssize_t bfq_max_budget_store(struct elevator_queue *e,
7487	const char *page, size_t count)
7488	{
7489	struct bfq_data *bfqd = e->elevator_data;
7490	unsigned long __data;
7491	int ret;
7492
7493	ret = bfq_var_store(var: &__data, (page));
7494	if (ret)
7495	return ret;
7496
7497	if (__data == 0)
7498	bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7499	else {
7500	if (__data > INT_MAX)
7501	__data = INT_MAX;
7502	bfqd->bfq_max_budget = __data;
7503	}
7504
7505	bfqd->bfq_user_max_budget = __data;
7506
7507	return count;
7508	}
7509
7510	/*
7511	* Leaving this name to preserve name compatibility with cfq
7512	* parameters, but this timeout is used for both sync and async.
7513	*/
7514	static ssize_t bfq_timeout_sync_store(struct elevator_queue *e,
7515	const char *page, size_t count)
7516	{
7517	struct bfq_data *bfqd = e->elevator_data;
7518	unsigned long __data;
7519	int ret;
7520
7521	ret = bfq_var_store(var: &__data, (page));
7522	if (ret)
7523	return ret;
7524
7525	if (__data < 1)
7526	__data = 1;
7527	else if (__data > INT_MAX)
7528	__data = INT_MAX;
7529
7530	bfqd->bfq_timeout = msecs_to_jiffies(m: __data);
7531	if (bfqd->bfq_user_max_budget == 0)
7532	bfqd->bfq_max_budget = bfq_calc_max_budget(bfqd);
7533
7534	return count;
7535	}
7536
7537	static ssize_t bfq_strict_guarantees_store(struct elevator_queue *e,
7538	const char *page, size_t count)
7539	{
7540	struct bfq_data *bfqd = e->elevator_data;
7541	unsigned long __data;
7542	int ret;
7543
7544	ret = bfq_var_store(var: &__data, (page));
7545	if (ret)
7546	return ret;
7547
7548	if (__data > 1)
7549	__data = 1;
7550	if (!bfqd->strict_guarantees && __data == 1
7551	&& bfqd->bfq_slice_idle < 8 * NSEC_PER_MSEC)
7552	bfqd->bfq_slice_idle = 8 * NSEC_PER_MSEC;
7553
7554	bfqd->strict_guarantees = __data;
7555
7556	return count;
7557	}
7558
7559	static ssize_t bfq_low_latency_store(struct elevator_queue *e,
7560	const char *page, size_t count)
7561	{
7562	struct bfq_data *bfqd = e->elevator_data;
7563	unsigned long __data;
7564	int ret;
7565
7566	ret = bfq_var_store(var: &__data, (page));
7567	if (ret)
7568	return ret;
7569
7570	if (__data > 1)
7571	__data = 1;
7572	if (__data == 0 && bfqd->low_latency != 0)
7573	bfq_end_wr(bfqd);
7574	bfqd->low_latency = __data;
7575
7576	return count;
7577	}
7578
7579	#define BFQ_ATTR(name) \
7580	__ATTR(name, 0644, bfq_##name##_show, bfq_##name##_store)
7581
7582	static struct elv_fs_entry bfq_attrs[] = {
7583	BFQ_ATTR(fifo_expire_sync),
7584	BFQ_ATTR(fifo_expire_async),
7585	BFQ_ATTR(back_seek_max),
7586	BFQ_ATTR(back_seek_penalty),
7587	BFQ_ATTR(slice_idle),
7588	BFQ_ATTR(slice_idle_us),
7589	BFQ_ATTR(max_budget),
7590	BFQ_ATTR(timeout_sync),
7591	BFQ_ATTR(strict_guarantees),
7592	BFQ_ATTR(low_latency),
7593	__ATTR_NULL
7594	};
7595
7596	static struct elevator_type iosched_bfq_mq = {
7597	.ops = {
7598	.limit_depth = bfq_limit_depth,
7599	.prepare_request = bfq_prepare_request,
7600	.requeue_request = bfq_finish_requeue_request,
7601	.finish_request = bfq_finish_request,
7602	.exit_icq = bfq_exit_icq,
7603	.insert_requests = bfq_insert_requests,
7604	.dispatch_request = bfq_dispatch_request,
7605	.next_request = elv_rb_latter_request,
7606	.former_request = elv_rb_former_request,
7607	.allow_merge = bfq_allow_bio_merge,
7608	.bio_merge = bfq_bio_merge,
7609	.request_merge = bfq_request_merge,
7610	.requests_merged = bfq_requests_merged,
7611	.request_merged = bfq_request_merged,
7612	.has_work = bfq_has_work,
7613	.depth_updated = bfq_depth_updated,
7614	.init_hctx = bfq_init_hctx,
7615	.init_sched = bfq_init_queue,
7616	.exit_sched = bfq_exit_queue,
7617	},
7618
7619	.icq_size = sizeof(struct bfq_io_cq),
7620	.icq_align = __alignof__(struct bfq_io_cq),
7621	.elevator_attrs = bfq_attrs,
7622	.elevator_name = "bfq",
7623	.elevator_owner = THIS_MODULE,
7624	};
7625	MODULE_ALIAS("bfq-iosched");
7626
7627	static int __init bfq_init(void)
7628	{
7629	int ret;
7630
7631	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7632	ret = blkcg_policy_register(pol: &blkcg_policy_bfq);
7633	if (ret)
7634	return ret;
7635	#endif
7636
7637	ret = -ENOMEM;
7638	if (bfq_slab_setup())
7639	goto err_pol_unreg;
7640
7641	/*
7642	* Times to load large popular applications for the typical
7643	* systems installed on the reference devices (see the
7644	* comments before the definition of the next
7645	* array). Actually, we use slightly lower values, as the
7646	* estimated peak rate tends to be smaller than the actual
7647	* peak rate. The reason for this last fact is that estimates
7648	* are computed over much shorter time intervals than the long
7649	* intervals typically used for benchmarking. Why? First, to
7650	* adapt more quickly to variations. Second, because an I/O
7651	* scheduler cannot rely on a peak-rate-evaluation workload to
7652	* be run for a long time.
7653	*/
7654	ref_wr_duration[0] = msecs_to_jiffies(m: 7000); /* actually 8 sec */
7655	ref_wr_duration[1] = msecs_to_jiffies(m: 2500); /* actually 3 sec */
7656
7657	ret = elv_register(&iosched_bfq_mq);
7658	if (ret)
7659	goto slab_kill;
7660
7661	return 0;
7662
7663	slab_kill:
7664	bfq_slab_kill();
7665	err_pol_unreg:
7666	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7667	blkcg_policy_unregister(pol: &blkcg_policy_bfq);
7668	#endif
7669	return ret;
7670	}
7671
7672	static void __exit bfq_exit(void)
7673	{
7674	elv_unregister(&iosched_bfq_mq);
7675	#ifdef CONFIG_BFQ_GROUP_IOSCHED
7676	blkcg_policy_unregister(pol: &blkcg_policy_bfq);
7677	#endif
7678	bfq_slab_kill();
7679	}
7680
7681	module_init(bfq_init);
7682	module_exit(bfq_exit);
7683
7684	MODULE_AUTHOR("Paolo Valente");
7685	MODULE_LICENSE("GPL");
7686	MODULE_DESCRIPTION("MQ Budget Fair Queueing I/O Scheduler");
7687