1// SPDX-License-Identifier: GPL-2.0
2/*
3 * blk-mq scheduling framework
4 *
5 * Copyright (C) 2016 Jens Axboe
6 */
7#include <linux/kernel.h>
8#include <linux/module.h>
9#include <linux/list_sort.h>
10
11#include <trace/events/block.h>
12
13#include "blk.h"
14#include "blk-mq.h"
15#include "blk-mq-debugfs.h"
16#include "blk-mq-sched.h"
17#include "blk-wbt.h"
18
19/*
20 * Mark a hardware queue as needing a restart.
21 */
22void blk_mq_sched_mark_restart_hctx(struct blk_mq_hw_ctx *hctx)
23{
24 if (test_bit(BLK_MQ_S_SCHED_RESTART, &hctx->state))
25 return;
26
27 set_bit(nr: BLK_MQ_S_SCHED_RESTART, addr: &hctx->state);
28}
29EXPORT_SYMBOL_GPL(blk_mq_sched_mark_restart_hctx);
30
31void __blk_mq_sched_restart(struct blk_mq_hw_ctx *hctx)
32{
33 clear_bit(nr: BLK_MQ_S_SCHED_RESTART, addr: &hctx->state);
34
35 /*
36 * Order clearing SCHED_RESTART and list_empty_careful(&hctx->dispatch)
37 * in blk_mq_run_hw_queue(). Its pair is the barrier in
38 * blk_mq_dispatch_rq_list(). So dispatch code won't see SCHED_RESTART,
39 * meantime new request added to hctx->dispatch is missed to check in
40 * blk_mq_run_hw_queue().
41 */
42 smp_mb();
43
44 blk_mq_run_hw_queue(hctx, async: true);
45}
46
47static int sched_rq_cmp(void *priv, const struct list_head *a,
48 const struct list_head *b)
49{
50 struct request *rqa = container_of(a, struct request, queuelist);
51 struct request *rqb = container_of(b, struct request, queuelist);
52
53 return rqa->mq_hctx > rqb->mq_hctx;
54}
55
56static bool blk_mq_dispatch_hctx_list(struct list_head *rq_list)
57{
58 struct blk_mq_hw_ctx *hctx =
59 list_first_entry(rq_list, struct request, queuelist)->mq_hctx;
60 struct request *rq;
61 LIST_HEAD(hctx_list);
62 unsigned int count = 0;
63
64 list_for_each_entry(rq, rq_list, queuelist) {
65 if (rq->mq_hctx != hctx) {
66 list_cut_before(list: &hctx_list, head: rq_list, entry: &rq->queuelist);
67 goto dispatch;
68 }
69 count++;
70 }
71 list_splice_tail_init(list: rq_list, head: &hctx_list);
72
73dispatch:
74 return blk_mq_dispatch_rq_list(hctx, &hctx_list, count);
75}
76
77#define BLK_MQ_BUDGET_DELAY 3 /* ms units */
78
79/*
80 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
81 * its queue by itself in its completion handler, so we don't need to
82 * restart queue if .get_budget() fails to get the budget.
83 *
84 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
85 * be run again. This is necessary to avoid starving flushes.
86 */
87static int __blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
88{
89 struct request_queue *q = hctx->queue;
90 struct elevator_queue *e = q->elevator;
91 bool multi_hctxs = false, run_queue = false;
92 bool dispatched = false, busy = false;
93 unsigned int max_dispatch;
94 LIST_HEAD(rq_list);
95 int count = 0;
96
97 if (hctx->dispatch_busy)
98 max_dispatch = 1;
99 else
100 max_dispatch = hctx->queue->nr_requests;
101
102 do {
103 struct request *rq;
104 int budget_token;
105
106 if (e->type->ops.has_work && !e->type->ops.has_work(hctx))
107 break;
108
109 if (!list_empty_careful(head: &hctx->dispatch)) {
110 busy = true;
111 break;
112 }
113
114 budget_token = blk_mq_get_dispatch_budget(q);
115 if (budget_token < 0)
116 break;
117
118 rq = e->type->ops.dispatch_request(hctx);
119 if (!rq) {
120 blk_mq_put_dispatch_budget(q, budget_token);
121 /*
122 * We're releasing without dispatching. Holding the
123 * budget could have blocked any "hctx"s with the
124 * same queue and if we didn't dispatch then there's
125 * no guarantee anyone will kick the queue. Kick it
126 * ourselves.
127 */
128 run_queue = true;
129 break;
130 }
131
132 blk_mq_set_rq_budget_token(rq, token: budget_token);
133
134 /*
135 * Now this rq owns the budget which has to be released
136 * if this rq won't be queued to driver via .queue_rq()
137 * in blk_mq_dispatch_rq_list().
138 */
139 list_add_tail(new: &rq->queuelist, head: &rq_list);
140 count++;
141 if (rq->mq_hctx != hctx)
142 multi_hctxs = true;
143
144 /*
145 * If we cannot get tag for the request, stop dequeueing
146 * requests from the IO scheduler. We are unlikely to be able
147 * to submit them anyway and it creates false impression for
148 * scheduling heuristics that the device can take more IO.
149 */
150 if (!blk_mq_get_driver_tag(rq))
151 break;
152 } while (count < max_dispatch);
153
154 if (!count) {
155 if (run_queue)
156 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
157 } else if (multi_hctxs) {
158 /*
159 * Requests from different hctx may be dequeued from some
160 * schedulers, such as bfq and deadline.
161 *
162 * Sort the requests in the list according to their hctx,
163 * dispatch batching requests from same hctx at a time.
164 */
165 list_sort(NULL, head: &rq_list, cmp: sched_rq_cmp);
166 do {
167 dispatched |= blk_mq_dispatch_hctx_list(rq_list: &rq_list);
168 } while (!list_empty(head: &rq_list));
169 } else {
170 dispatched = blk_mq_dispatch_rq_list(hctx, &rq_list, count);
171 }
172
173 if (busy)
174 return -EAGAIN;
175 return !!dispatched;
176}
177
178static int blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
179{
180 unsigned long end = jiffies + HZ;
181 int ret;
182
183 do {
184 ret = __blk_mq_do_dispatch_sched(hctx);
185 if (ret != 1)
186 break;
187 if (need_resched() || time_is_before_jiffies(end)) {
188 blk_mq_delay_run_hw_queue(hctx, msecs: 0);
189 break;
190 }
191 } while (1);
192
193 return ret;
194}
195
196static struct blk_mq_ctx *blk_mq_next_ctx(struct blk_mq_hw_ctx *hctx,
197 struct blk_mq_ctx *ctx)
198{
199 unsigned short idx = ctx->index_hw[hctx->type];
200
201 if (++idx == hctx->nr_ctx)
202 idx = 0;
203
204 return hctx->ctxs[idx];
205}
206
207/*
208 * Only SCSI implements .get_budget and .put_budget, and SCSI restarts
209 * its queue by itself in its completion handler, so we don't need to
210 * restart queue if .get_budget() fails to get the budget.
211 *
212 * Returns -EAGAIN if hctx->dispatch was found non-empty and run_work has to
213 * be run again. This is necessary to avoid starving flushes.
214 */
215static int blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
216{
217 struct request_queue *q = hctx->queue;
218 LIST_HEAD(rq_list);
219 struct blk_mq_ctx *ctx = READ_ONCE(hctx->dispatch_from);
220 int ret = 0;
221 struct request *rq;
222
223 do {
224 int budget_token;
225
226 if (!list_empty_careful(head: &hctx->dispatch)) {
227 ret = -EAGAIN;
228 break;
229 }
230
231 if (!sbitmap_any_bit_set(sb: &hctx->ctx_map))
232 break;
233
234 budget_token = blk_mq_get_dispatch_budget(q);
235 if (budget_token < 0)
236 break;
237
238 rq = blk_mq_dequeue_from_ctx(hctx, start: ctx);
239 if (!rq) {
240 blk_mq_put_dispatch_budget(q, budget_token);
241 /*
242 * We're releasing without dispatching. Holding the
243 * budget could have blocked any "hctx"s with the
244 * same queue and if we didn't dispatch then there's
245 * no guarantee anyone will kick the queue. Kick it
246 * ourselves.
247 */
248 blk_mq_delay_run_hw_queues(q, BLK_MQ_BUDGET_DELAY);
249 break;
250 }
251
252 blk_mq_set_rq_budget_token(rq, token: budget_token);
253
254 /*
255 * Now this rq owns the budget which has to be released
256 * if this rq won't be queued to driver via .queue_rq()
257 * in blk_mq_dispatch_rq_list().
258 */
259 list_add(new: &rq->queuelist, head: &rq_list);
260
261 /* round robin for fair dispatch */
262 ctx = blk_mq_next_ctx(hctx, ctx: rq->mq_ctx);
263
264 } while (blk_mq_dispatch_rq_list(hctx: rq->mq_hctx, &rq_list, 1));
265
266 WRITE_ONCE(hctx->dispatch_from, ctx);
267 return ret;
268}
269
270static int __blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
271{
272 bool need_dispatch = false;
273 LIST_HEAD(rq_list);
274
275 /*
276 * If we have previous entries on our dispatch list, grab them first for
277 * more fair dispatch.
278 */
279 if (!list_empty_careful(head: &hctx->dispatch)) {
280 spin_lock(lock: &hctx->lock);
281 if (!list_empty(head: &hctx->dispatch))
282 list_splice_init(list: &hctx->dispatch, head: &rq_list);
283 spin_unlock(lock: &hctx->lock);
284 }
285
286 /*
287 * Only ask the scheduler for requests, if we didn't have residual
288 * requests from the dispatch list. This is to avoid the case where
289 * we only ever dispatch a fraction of the requests available because
290 * of low device queue depth. Once we pull requests out of the IO
291 * scheduler, we can no longer merge or sort them. So it's best to
292 * leave them there for as long as we can. Mark the hw queue as
293 * needing a restart in that case.
294 *
295 * We want to dispatch from the scheduler if there was nothing
296 * on the dispatch list or we were able to dispatch from the
297 * dispatch list.
298 */
299 if (!list_empty(head: &rq_list)) {
300 blk_mq_sched_mark_restart_hctx(hctx);
301 if (!blk_mq_dispatch_rq_list(hctx, &rq_list, 0))
302 return 0;
303 need_dispatch = true;
304 } else {
305 need_dispatch = hctx->dispatch_busy;
306 }
307
308 if (hctx->queue->elevator)
309 return blk_mq_do_dispatch_sched(hctx);
310
311 /* dequeue request one by one from sw queue if queue is busy */
312 if (need_dispatch)
313 return blk_mq_do_dispatch_ctx(hctx);
314 blk_mq_flush_busy_ctxs(hctx, list: &rq_list);
315 blk_mq_dispatch_rq_list(hctx, &rq_list, 0);
316 return 0;
317}
318
319void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
320{
321 struct request_queue *q = hctx->queue;
322
323 /* RCU or SRCU read lock is needed before checking quiesced flag */
324 if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
325 return;
326
327 hctx->run++;
328
329 /*
330 * A return of -EAGAIN is an indication that hctx->dispatch is not
331 * empty and we must run again in order to avoid starving flushes.
332 */
333 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN) {
334 if (__blk_mq_sched_dispatch_requests(hctx) == -EAGAIN)
335 blk_mq_run_hw_queue(hctx, async: true);
336 }
337}
338
339bool blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio,
340 unsigned int nr_segs)
341{
342 struct elevator_queue *e = q->elevator;
343 struct blk_mq_ctx *ctx;
344 struct blk_mq_hw_ctx *hctx;
345 bool ret = false;
346 enum hctx_type type;
347
348 if (e && e->type->ops.bio_merge) {
349 ret = e->type->ops.bio_merge(q, bio, nr_segs);
350 goto out_put;
351 }
352
353 ctx = blk_mq_get_ctx(q);
354 hctx = blk_mq_map_queue(q, opf: bio->bi_opf, ctx);
355 type = hctx->type;
356 if (!(hctx->flags & BLK_MQ_F_SHOULD_MERGE) ||
357 list_empty_careful(head: &ctx->rq_lists[type]))
358 goto out_put;
359
360 /* default per sw-queue merge */
361 spin_lock(lock: &ctx->lock);
362 /*
363 * Reverse check our software queue for entries that we could
364 * potentially merge with. Currently includes a hand-wavy stop
365 * count of 8, to not spend too much time checking for merges.
366 */
367 if (blk_bio_list_merge(q, list: &ctx->rq_lists[type], bio, nr_segs))
368 ret = true;
369
370 spin_unlock(lock: &ctx->lock);
371out_put:
372 return ret;
373}
374
375bool blk_mq_sched_try_insert_merge(struct request_queue *q, struct request *rq,
376 struct list_head *free)
377{
378 return rq_mergeable(rq) && elv_attempt_insert_merge(q, rq, free);
379}
380EXPORT_SYMBOL_GPL(blk_mq_sched_try_insert_merge);
381
382static int blk_mq_sched_alloc_map_and_rqs(struct request_queue *q,
383 struct blk_mq_hw_ctx *hctx,
384 unsigned int hctx_idx)
385{
386 if (blk_mq_is_shared_tags(flags: q->tag_set->flags)) {
387 hctx->sched_tags = q->sched_shared_tags;
388 return 0;
389 }
390
391 hctx->sched_tags = blk_mq_alloc_map_and_rqs(set: q->tag_set, hctx_idx,
392 depth: q->nr_requests);
393
394 if (!hctx->sched_tags)
395 return -ENOMEM;
396 return 0;
397}
398
399static void blk_mq_exit_sched_shared_tags(struct request_queue *queue)
400{
401 blk_mq_free_rq_map(tags: queue->sched_shared_tags);
402 queue->sched_shared_tags = NULL;
403}
404
405/* called in queue's release handler, tagset has gone away */
406static void blk_mq_sched_tags_teardown(struct request_queue *q, unsigned int flags)
407{
408 struct blk_mq_hw_ctx *hctx;
409 unsigned long i;
410
411 queue_for_each_hw_ctx(q, hctx, i) {
412 if (hctx->sched_tags) {
413 if (!blk_mq_is_shared_tags(flags))
414 blk_mq_free_rq_map(tags: hctx->sched_tags);
415 hctx->sched_tags = NULL;
416 }
417 }
418
419 if (blk_mq_is_shared_tags(flags))
420 blk_mq_exit_sched_shared_tags(queue: q);
421}
422
423static int blk_mq_init_sched_shared_tags(struct request_queue *queue)
424{
425 struct blk_mq_tag_set *set = queue->tag_set;
426
427 /*
428 * Set initial depth at max so that we don't need to reallocate for
429 * updating nr_requests.
430 */
431 queue->sched_shared_tags = blk_mq_alloc_map_and_rqs(set,
432 BLK_MQ_NO_HCTX_IDX,
433 MAX_SCHED_RQ);
434 if (!queue->sched_shared_tags)
435 return -ENOMEM;
436
437 blk_mq_tag_update_sched_shared_tags(q: queue);
438
439 return 0;
440}
441
442/* caller must have a reference to @e, will grab another one if successful */
443int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
444{
445 unsigned int flags = q->tag_set->flags;
446 struct blk_mq_hw_ctx *hctx;
447 struct elevator_queue *eq;
448 unsigned long i;
449 int ret;
450
451 /*
452 * Default to double of smaller one between hw queue_depth and 128,
453 * since we don't split into sync/async like the old code did.
454 * Additionally, this is a per-hw queue depth.
455 */
456 q->nr_requests = 2 * min_t(unsigned int, q->tag_set->queue_depth,
457 BLKDEV_DEFAULT_RQ);
458
459 if (blk_mq_is_shared_tags(flags)) {
460 ret = blk_mq_init_sched_shared_tags(queue: q);
461 if (ret)
462 return ret;
463 }
464
465 queue_for_each_hw_ctx(q, hctx, i) {
466 ret = blk_mq_sched_alloc_map_and_rqs(q, hctx, hctx_idx: i);
467 if (ret)
468 goto err_free_map_and_rqs;
469 }
470
471 ret = e->ops.init_sched(q, e);
472 if (ret)
473 goto err_free_map_and_rqs;
474
475 mutex_lock(&q->debugfs_mutex);
476 blk_mq_debugfs_register_sched(q);
477 mutex_unlock(lock: &q->debugfs_mutex);
478
479 queue_for_each_hw_ctx(q, hctx, i) {
480 if (e->ops.init_hctx) {
481 ret = e->ops.init_hctx(hctx, i);
482 if (ret) {
483 eq = q->elevator;
484 blk_mq_sched_free_rqs(q);
485 blk_mq_exit_sched(q, e: eq);
486 kobject_put(kobj: &eq->kobj);
487 return ret;
488 }
489 }
490 mutex_lock(&q->debugfs_mutex);
491 blk_mq_debugfs_register_sched_hctx(q, hctx);
492 mutex_unlock(lock: &q->debugfs_mutex);
493 }
494
495 return 0;
496
497err_free_map_and_rqs:
498 blk_mq_sched_free_rqs(q);
499 blk_mq_sched_tags_teardown(q, flags);
500
501 q->elevator = NULL;
502 return ret;
503}
504
505/*
506 * called in either blk_queue_cleanup or elevator_switch, tagset
507 * is required for freeing requests
508 */
509void blk_mq_sched_free_rqs(struct request_queue *q)
510{
511 struct blk_mq_hw_ctx *hctx;
512 unsigned long i;
513
514 if (blk_mq_is_shared_tags(flags: q->tag_set->flags)) {
515 blk_mq_free_rqs(set: q->tag_set, tags: q->sched_shared_tags,
516 BLK_MQ_NO_HCTX_IDX);
517 } else {
518 queue_for_each_hw_ctx(q, hctx, i) {
519 if (hctx->sched_tags)
520 blk_mq_free_rqs(set: q->tag_set,
521 tags: hctx->sched_tags, hctx_idx: i);
522 }
523 }
524}
525
526void blk_mq_exit_sched(struct request_queue *q, struct elevator_queue *e)
527{
528 struct blk_mq_hw_ctx *hctx;
529 unsigned long i;
530 unsigned int flags = 0;
531
532 queue_for_each_hw_ctx(q, hctx, i) {
533 mutex_lock(&q->debugfs_mutex);
534 blk_mq_debugfs_unregister_sched_hctx(hctx);
535 mutex_unlock(lock: &q->debugfs_mutex);
536
537 if (e->type->ops.exit_hctx && hctx->sched_data) {
538 e->type->ops.exit_hctx(hctx, i);
539 hctx->sched_data = NULL;
540 }
541 flags = hctx->flags;
542 }
543
544 mutex_lock(&q->debugfs_mutex);
545 blk_mq_debugfs_unregister_sched(q);
546 mutex_unlock(lock: &q->debugfs_mutex);
547
548 if (e->type->ops.exit_sched)
549 e->type->ops.exit_sched(e);
550 blk_mq_sched_tags_teardown(q, flags);
551 q->elevator = NULL;
552}
553

source code of linux/block/blk-mq-sched.c