1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (C) 2013 Cisco Systems, Inc, 2013.
3 *
4 * Author: Vijay Subramanian <vijaynsu@cisco.com>
5 * Author: Mythili Prabhu <mysuryan@cisco.com>
6 *
7 * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
8 * University of Oslo, Norway.
9 *
10 * References:
11 * RFC 8033: https://tools.ietf.org/html/rfc8033
12 */
13
14#include <linux/module.h>
15#include <linux/slab.h>
16#include <linux/types.h>
17#include <linux/kernel.h>
18#include <linux/errno.h>
19#include <linux/skbuff.h>
20#include <net/pkt_sched.h>
21#include <net/inet_ecn.h>
22#include <net/pie.h>
23
24/* private data for the Qdisc */
25struct pie_sched_data {
26 struct pie_vars vars;
27 struct pie_params params;
28 struct pie_stats stats;
29 struct timer_list adapt_timer;
30 struct Qdisc *sch;
31};
32
33bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
34 struct pie_vars *vars, u32 backlog, u32 packet_size)
35{
36 u64 rnd;
37 u64 local_prob = vars->prob;
38 u32 mtu = psched_mtu(dev: qdisc_dev(qdisc: sch));
39
40 /* If there is still burst allowance left skip random early drop */
41 if (vars->burst_time > 0)
42 return false;
43
44 /* If current delay is less than half of target, and
45 * if drop prob is low already, disable early_drop
46 */
47 if ((vars->qdelay < params->target / 2) &&
48 (vars->prob < MAX_PROB / 5))
49 return false;
50
51 /* If we have fewer than 2 mtu-sized packets, disable pie_drop_early,
52 * similar to min_th in RED
53 */
54 if (backlog < 2 * mtu)
55 return false;
56
57 /* If bytemode is turned on, use packet size to compute new
58 * probablity. Smaller packets will have lower drop prob in this case
59 */
60 if (params->bytemode && packet_size <= mtu)
61 local_prob = (u64)packet_size * div_u64(dividend: local_prob, divisor: mtu);
62 else
63 local_prob = vars->prob;
64
65 if (local_prob == 0)
66 vars->accu_prob = 0;
67 else
68 vars->accu_prob += local_prob;
69
70 if (vars->accu_prob < (MAX_PROB / 100) * 85)
71 return false;
72 if (vars->accu_prob >= (MAX_PROB / 2) * 17)
73 return true;
74
75 get_random_bytes(buf: &rnd, len: 8);
76 if ((rnd >> BITS_PER_BYTE) < local_prob) {
77 vars->accu_prob = 0;
78 return true;
79 }
80
81 return false;
82}
83EXPORT_SYMBOL_GPL(pie_drop_early);
84
85static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
86 struct sk_buff **to_free)
87{
88 enum skb_drop_reason reason = SKB_DROP_REASON_QDISC_OVERLIMIT;
89 struct pie_sched_data *q = qdisc_priv(sch);
90 bool enqueue = false;
91
92 if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
93 q->stats.overlimit++;
94 goto out;
95 }
96
97 reason = SKB_DROP_REASON_QDISC_CONGESTED;
98
99 if (!pie_drop_early(sch, &q->params, &q->vars, sch->qstats.backlog,
100 skb->len)) {
101 enqueue = true;
102 } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
103 INET_ECN_set_ce(skb)) {
104 /* If packet is ecn capable, mark it if drop probability
105 * is lower than 10%, else drop it.
106 */
107 q->stats.ecn_mark++;
108 enqueue = true;
109 }
110
111 /* we can enqueue the packet */
112 if (enqueue) {
113 /* Set enqueue time only when dq_rate_estimator is disabled. */
114 if (!q->params.dq_rate_estimator)
115 pie_set_enqueue_time(skb);
116
117 q->stats.packets_in++;
118 if (qdisc_qlen(q: sch) > q->stats.maxq)
119 q->stats.maxq = qdisc_qlen(q: sch);
120
121 return qdisc_enqueue_tail(skb, sch);
122 }
123
124out:
125 q->stats.dropped++;
126 q->vars.accu_prob = 0;
127 return qdisc_drop_reason(skb, sch, to_free, reason);
128}
129
130static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
131 [TCA_PIE_TARGET] = {.type = NLA_U32},
132 [TCA_PIE_LIMIT] = {.type = NLA_U32},
133 [TCA_PIE_TUPDATE] = {.type = NLA_U32},
134 [TCA_PIE_ALPHA] = {.type = NLA_U32},
135 [TCA_PIE_BETA] = {.type = NLA_U32},
136 [TCA_PIE_ECN] = {.type = NLA_U32},
137 [TCA_PIE_BYTEMODE] = {.type = NLA_U32},
138 [TCA_PIE_DQ_RATE_ESTIMATOR] = {.type = NLA_U32},
139};
140
141static int pie_change(struct Qdisc *sch, struct nlattr *opt,
142 struct netlink_ext_ack *extack)
143{
144 unsigned int dropped_pkts = 0, dropped_bytes = 0;
145 struct pie_sched_data *q = qdisc_priv(sch);
146 struct nlattr *tb[TCA_PIE_MAX + 1];
147 int err;
148
149 err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, nla: opt, policy: pie_policy,
150 NULL);
151 if (err < 0)
152 return err;
153
154 sch_tree_lock(q: sch);
155
156 /* convert from microseconds to pschedtime */
157 if (tb[TCA_PIE_TARGET]) {
158 /* target is in us */
159 u32 target = nla_get_u32(nla: tb[TCA_PIE_TARGET]);
160
161 /* convert to pschedtime */
162 WRITE_ONCE(q->params.target,
163 PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC));
164 }
165
166 /* tupdate is in jiffies */
167 if (tb[TCA_PIE_TUPDATE])
168 WRITE_ONCE(q->params.tupdate,
169 usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE])));
170
171 if (tb[TCA_PIE_LIMIT]) {
172 u32 limit = nla_get_u32(nla: tb[TCA_PIE_LIMIT]);
173
174 WRITE_ONCE(q->params.limit, limit);
175 WRITE_ONCE(sch->limit, limit);
176 }
177
178 if (tb[TCA_PIE_ALPHA])
179 WRITE_ONCE(q->params.alpha, nla_get_u32(tb[TCA_PIE_ALPHA]));
180
181 if (tb[TCA_PIE_BETA])
182 WRITE_ONCE(q->params.beta, nla_get_u32(tb[TCA_PIE_BETA]));
183
184 if (tb[TCA_PIE_ECN])
185 WRITE_ONCE(q->params.ecn, nla_get_u32(tb[TCA_PIE_ECN]));
186
187 if (tb[TCA_PIE_BYTEMODE])
188 WRITE_ONCE(q->params.bytemode,
189 nla_get_u32(tb[TCA_PIE_BYTEMODE]));
190
191 if (tb[TCA_PIE_DQ_RATE_ESTIMATOR])
192 WRITE_ONCE(q->params.dq_rate_estimator,
193 nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]));
194
195 /* Drop excess packets if new limit is lower */
196 while (sch->q.qlen > sch->limit) {
197 struct sk_buff *skb = qdisc_dequeue_internal(sch, direct: true);
198
199 if (!skb)
200 break;
201
202 dropped_pkts++;
203 dropped_bytes += qdisc_pkt_len(skb);
204 rtnl_qdisc_drop(skb, sch);
205 }
206 qdisc_tree_reduce_backlog(qdisc: sch, n: dropped_pkts, len: dropped_bytes);
207
208 sch_tree_unlock(q: sch);
209 return 0;
210}
211
212void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
213 struct pie_vars *vars, u32 backlog)
214{
215 psched_time_t now = psched_get_time();
216 u32 dtime = 0;
217
218 /* If dq_rate_estimator is disabled, calculate qdelay using the
219 * packet timestamp.
220 */
221 if (!params->dq_rate_estimator) {
222 vars->qdelay = now - pie_get_enqueue_time(skb);
223
224 if (vars->dq_tstamp != DTIME_INVALID)
225 dtime = now - vars->dq_tstamp;
226
227 vars->dq_tstamp = now;
228
229 if (backlog == 0)
230 vars->qdelay = 0;
231
232 if (dtime == 0)
233 return;
234
235 goto burst_allowance_reduction;
236 }
237
238 /* If current queue is about 10 packets or more and dq_count is unset
239 * we have enough packets to calculate the drain rate. Save
240 * current time as dq_tstamp and start measurement cycle.
241 */
242 if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
243 vars->dq_tstamp = psched_get_time();
244 vars->dq_count = 0;
245 }
246
247 /* Calculate the average drain rate from this value. If queue length
248 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset
249 * the dq_count to -1 as we don't have enough packets to calculate the
250 * drain rate anymore. The following if block is entered only when we
251 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
252 * and we calculate the drain rate for the threshold here. dq_count is
253 * in bytes, time difference in psched_time, hence rate is in
254 * bytes/psched_time.
255 */
256 if (vars->dq_count != DQCOUNT_INVALID) {
257 vars->dq_count += skb->len;
258
259 if (vars->dq_count >= QUEUE_THRESHOLD) {
260 u32 count = vars->dq_count << PIE_SCALE;
261
262 dtime = now - vars->dq_tstamp;
263
264 if (dtime == 0)
265 return;
266
267 count = count / dtime;
268
269 if (vars->avg_dq_rate == 0)
270 vars->avg_dq_rate = count;
271 else
272 vars->avg_dq_rate =
273 (vars->avg_dq_rate -
274 (vars->avg_dq_rate >> 3)) + (count >> 3);
275
276 /* If the queue has receded below the threshold, we hold
277 * on to the last drain rate calculated, else we reset
278 * dq_count to 0 to re-enter the if block when the next
279 * packet is dequeued
280 */
281 if (backlog < QUEUE_THRESHOLD) {
282 vars->dq_count = DQCOUNT_INVALID;
283 } else {
284 vars->dq_count = 0;
285 vars->dq_tstamp = psched_get_time();
286 }
287
288 goto burst_allowance_reduction;
289 }
290 }
291
292 return;
293
294burst_allowance_reduction:
295 if (vars->burst_time > 0) {
296 if (vars->burst_time > dtime)
297 vars->burst_time -= dtime;
298 else
299 vars->burst_time = 0;
300 }
301}
302EXPORT_SYMBOL_GPL(pie_process_dequeue);
303
304void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
305 u32 backlog)
306{
307 psched_time_t qdelay = 0; /* in pschedtime */
308 psched_time_t qdelay_old = 0; /* in pschedtime */
309 s64 delta = 0; /* determines the change in probability */
310 u64 oldprob;
311 u64 alpha, beta;
312 u32 power;
313 bool update_prob = true;
314
315 if (params->dq_rate_estimator) {
316 qdelay_old = vars->qdelay;
317 vars->qdelay_old = vars->qdelay;
318
319 if (vars->avg_dq_rate > 0)
320 qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate;
321 else
322 qdelay = 0;
323 } else {
324 qdelay = vars->qdelay;
325 qdelay_old = vars->qdelay_old;
326 }
327
328 /* If qdelay is zero and backlog is not, it means backlog is very small,
329 * so we do not update probability in this round.
330 */
331 if (qdelay == 0 && backlog != 0)
332 update_prob = false;
333
334 /* In the algorithm, alpha and beta are between 0 and 2 with typical
335 * value for alpha as 0.125. In this implementation, we use values 0-32
336 * passed from user space to represent this. Also, alpha and beta have
337 * unit of HZ and need to be scaled before they can used to update
338 * probability. alpha/beta are updated locally below by scaling down
339 * by 16 to come to 0-2 range.
340 */
341 alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
342 beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
343
344 /* We scale alpha and beta differently depending on how heavy the
345 * congestion is. Please see RFC 8033 for details.
346 */
347 if (vars->prob < MAX_PROB / 10) {
348 alpha >>= 1;
349 beta >>= 1;
350
351 power = 100;
352 while (vars->prob < div_u64(MAX_PROB, divisor: power) &&
353 power <= 1000000) {
354 alpha >>= 2;
355 beta >>= 2;
356 power *= 10;
357 }
358 }
359
360 /* alpha and beta should be between 0 and 32, in multiples of 1/16 */
361 delta += alpha * (qdelay - params->target);
362 delta += beta * (qdelay - qdelay_old);
363
364 oldprob = vars->prob;
365
366 /* to ensure we increase probability in steps of no more than 2% */
367 if (delta > (s64)(MAX_PROB / (100 / 2)) &&
368 vars->prob >= MAX_PROB / 10)
369 delta = (MAX_PROB / 100) * 2;
370
371 /* Non-linear drop:
372 * Tune drop probability to increase quickly for high delays(>= 250ms)
373 * 250ms is derived through experiments and provides error protection
374 */
375
376 if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
377 delta += MAX_PROB / (100 / 2);
378
379 vars->prob += delta;
380
381 if (delta > 0) {
382 /* prevent overflow */
383 if (vars->prob < oldprob) {
384 vars->prob = MAX_PROB;
385 /* Prevent normalization error. If probability is at
386 * maximum value already, we normalize it here, and
387 * skip the check to do a non-linear drop in the next
388 * section.
389 */
390 update_prob = false;
391 }
392 } else {
393 /* prevent underflow */
394 if (vars->prob > oldprob)
395 vars->prob = 0;
396 }
397
398 /* Non-linear drop in probability: Reduce drop probability quickly if
399 * delay is 0 for 2 consecutive Tupdate periods.
400 */
401
402 if (qdelay == 0 && qdelay_old == 0 && update_prob)
403 /* Reduce drop probability to 98.4% */
404 vars->prob -= vars->prob / 64;
405
406 vars->qdelay = qdelay;
407 vars->backlog_old = backlog;
408
409 /* We restart the measurement cycle if the following conditions are met
410 * 1. If the delay has been low for 2 consecutive Tupdate periods
411 * 2. Calculated drop probability is zero
412 * 3. If average dq_rate_estimator is enabled, we have at least one
413 * estimate for the avg_dq_rate ie., is a non-zero value
414 */
415 if ((vars->qdelay < params->target / 2) &&
416 (vars->qdelay_old < params->target / 2) &&
417 vars->prob == 0 &&
418 (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) {
419 pie_vars_init(vars);
420 }
421
422 if (!params->dq_rate_estimator)
423 vars->qdelay_old = qdelay;
424}
425EXPORT_SYMBOL_GPL(pie_calculate_probability);
426
427static void pie_timer(struct timer_list *t)
428{
429 struct pie_sched_data *q = timer_container_of(q, t, adapt_timer);
430 struct Qdisc *sch = q->sch;
431 spinlock_t *root_lock;
432
433 rcu_read_lock();
434 root_lock = qdisc_lock(qdisc: qdisc_root_sleeping(qdisc: sch));
435 spin_lock(lock: root_lock);
436 pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog);
437
438 /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
439 if (q->params.tupdate)
440 mod_timer(timer: &q->adapt_timer, expires: jiffies + q->params.tupdate);
441 spin_unlock(lock: root_lock);
442 rcu_read_unlock();
443}
444
445static int pie_init(struct Qdisc *sch, struct nlattr *opt,
446 struct netlink_ext_ack *extack)
447{
448 struct pie_sched_data *q = qdisc_priv(sch);
449
450 pie_params_init(params: &q->params);
451 pie_vars_init(vars: &q->vars);
452 sch->limit = q->params.limit;
453
454 q->sch = sch;
455 timer_setup(&q->adapt_timer, pie_timer, 0);
456
457 if (opt) {
458 int err = pie_change(sch, opt, extack);
459
460 if (err)
461 return err;
462 }
463
464 mod_timer(timer: &q->adapt_timer, expires: jiffies + HZ / 2);
465 return 0;
466}
467
468static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
469{
470 struct pie_sched_data *q = qdisc_priv(sch);
471 struct nlattr *opts;
472
473 opts = nla_nest_start_noflag(skb, attrtype: TCA_OPTIONS);
474 if (!opts)
475 goto nla_put_failure;
476
477 /* convert target from pschedtime to us */
478 if (nla_put_u32(skb, attrtype: TCA_PIE_TARGET,
479 value: ((u32)PSCHED_TICKS2NS(READ_ONCE(q->params.target))) /
480 NSEC_PER_USEC) ||
481 nla_put_u32(skb, attrtype: TCA_PIE_LIMIT, READ_ONCE(sch->limit)) ||
482 nla_put_u32(skb, attrtype: TCA_PIE_TUPDATE,
483 value: jiffies_to_usecs(READ_ONCE(q->params.tupdate))) ||
484 nla_put_u32(skb, attrtype: TCA_PIE_ALPHA, READ_ONCE(q->params.alpha)) ||
485 nla_put_u32(skb, attrtype: TCA_PIE_BETA, READ_ONCE(q->params.beta)) ||
486 nla_put_u32(skb, attrtype: TCA_PIE_ECN, value: q->params.ecn) ||
487 nla_put_u32(skb, attrtype: TCA_PIE_BYTEMODE,
488 READ_ONCE(q->params.bytemode)) ||
489 nla_put_u32(skb, attrtype: TCA_PIE_DQ_RATE_ESTIMATOR,
490 READ_ONCE(q->params.dq_rate_estimator)))
491 goto nla_put_failure;
492
493 return nla_nest_end(skb, start: opts);
494
495nla_put_failure:
496 nla_nest_cancel(skb, start: opts);
497 return -1;
498}
499
500static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
501{
502 struct pie_sched_data *q = qdisc_priv(sch);
503 struct tc_pie_xstats st = {
504 .prob = q->vars.prob << BITS_PER_BYTE,
505 .delay = ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) /
506 NSEC_PER_USEC,
507 .packets_in = q->stats.packets_in,
508 .overlimit = q->stats.overlimit,
509 .maxq = q->stats.maxq,
510 .dropped = q->stats.dropped,
511 .ecn_mark = q->stats.ecn_mark,
512 };
513
514 /* avg_dq_rate is only valid if dq_rate_estimator is enabled */
515 st.dq_rate_estimating = q->params.dq_rate_estimator;
516
517 /* unscale and return dq_rate in bytes per sec */
518 if (q->params.dq_rate_estimator)
519 st.avg_dq_rate = q->vars.avg_dq_rate *
520 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE;
521
522 return gnet_stats_copy_app(d, st: &st, len: sizeof(st));
523}
524
525static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
526{
527 struct pie_sched_data *q = qdisc_priv(sch);
528 struct sk_buff *skb = qdisc_dequeue_head(sch);
529
530 if (!skb)
531 return NULL;
532
533 pie_process_dequeue(skb, &q->params, &q->vars, sch->qstats.backlog);
534 return skb;
535}
536
537static void pie_reset(struct Qdisc *sch)
538{
539 struct pie_sched_data *q = qdisc_priv(sch);
540
541 qdisc_reset_queue(sch);
542 pie_vars_init(vars: &q->vars);
543}
544
545static void pie_destroy(struct Qdisc *sch)
546{
547 struct pie_sched_data *q = qdisc_priv(sch);
548
549 q->params.tupdate = 0;
550 timer_delete_sync(timer: &q->adapt_timer);
551}
552
553static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
554 .id = "pie",
555 .priv_size = sizeof(struct pie_sched_data),
556 .enqueue = pie_qdisc_enqueue,
557 .dequeue = pie_qdisc_dequeue,
558 .peek = qdisc_peek_dequeued,
559 .init = pie_init,
560 .destroy = pie_destroy,
561 .reset = pie_reset,
562 .change = pie_change,
563 .dump = pie_dump,
564 .dump_stats = pie_dump_stats,
565 .owner = THIS_MODULE,
566};
567MODULE_ALIAS_NET_SCH("pie");
568
569static int __init pie_module_init(void)
570{
571 return register_qdisc(qops: &pie_qdisc_ops);
572}
573
574static void __exit pie_module_exit(void)
575{
576 unregister_qdisc(qops: &pie_qdisc_ops);
577}
578
579module_init(pie_module_init);
580module_exit(pie_module_exit);
581
582MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
583MODULE_AUTHOR("Vijay Subramanian");
584MODULE_AUTHOR("Mythili Prabhu");
585MODULE_LICENSE("GPL");
586

source code of linux/net/sched/sch_pie.c