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