xref: /linux/net/sched/sch_pie.c (revision f86fd32d) 
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 */
25 struct 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 
33 bool pie_drop_early(struct Qdisc *sch, struct pie_params *params,
34 		    struct pie_vars *vars, u32 qlen, 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 (qlen < 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 		vars->accu_prob_overflows = 0;
68 	}
69 
70 	if (local_prob > MAX_PROB - vars->accu_prob)
71 		vars->accu_prob_overflows++;
72 
73 	vars->accu_prob += local_prob;
74 
75 	if (vars->accu_prob_overflows == 0 &&
76 	    vars->accu_prob < (MAX_PROB / 100) * 85)
77 		return false;
78 	if (vars->accu_prob_overflows == 8 &&
79 	    vars->accu_prob >= MAX_PROB / 2)
80 		return true;
81 
82 	prandom_bytes(&rnd, 8);
83 	if (rnd < local_prob) {
84 		vars->accu_prob = 0;
85 		vars->accu_prob_overflows = 0;
86 		return true;
87 	}
88 
89 	return false;
90 }
91 EXPORT_SYMBOL_GPL(pie_drop_early);
92 
93 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
94 			     struct sk_buff **to_free)
95 {
96 	struct pie_sched_data *q = qdisc_priv(sch);
97 	bool enqueue = false;
98 
99 	if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
100 		q->stats.overlimit++;
101 		goto out;
102 	}
103 
104 	if (!pie_drop_early(sch, &q->params, &q->vars, sch->qstats.backlog,
105 			    skb->len)) {
106 		enqueue = true;
107 	} else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
108 		   INET_ECN_set_ce(skb)) {
109 		/* If packet is ecn capable, mark it if drop probability
110 		 * is lower than 10%, else drop it.
111 		 */
112 		q->stats.ecn_mark++;
113 		enqueue = true;
114 	}
115 
116 	/* we can enqueue the packet */
117 	if (enqueue) {
118 		/* Set enqueue time only when dq_rate_estimator is disabled. */
119 		if (!q->params.dq_rate_estimator)
120 			pie_set_enqueue_time(skb);
121 
122 		q->stats.packets_in++;
123 		if (qdisc_qlen(sch) > q->stats.maxq)
124 			q->stats.maxq = qdisc_qlen(sch);
125 
126 		return qdisc_enqueue_tail(skb, sch);
127 	}
128 
129 out:
130 	q->stats.dropped++;
131 	q->vars.accu_prob = 0;
132 	q->vars.accu_prob_overflows = 0;
133 	return qdisc_drop(skb, sch, to_free);
134 }
135 
136 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
137 	[TCA_PIE_TARGET]		= {.type = NLA_U32},
138 	[TCA_PIE_LIMIT]			= {.type = NLA_U32},
139 	[TCA_PIE_TUPDATE]		= {.type = NLA_U32},
140 	[TCA_PIE_ALPHA]			= {.type = NLA_U32},
141 	[TCA_PIE_BETA]			= {.type = NLA_U32},
142 	[TCA_PIE_ECN]			= {.type = NLA_U32},
143 	[TCA_PIE_BYTEMODE]		= {.type = NLA_U32},
144 	[TCA_PIE_DQ_RATE_ESTIMATOR]	= {.type = NLA_U32},
145 };
146 
147 static int pie_change(struct Qdisc *sch, struct nlattr *opt,
148 		      struct netlink_ext_ack *extack)
149 {
150 	struct pie_sched_data *q = qdisc_priv(sch);
151 	struct nlattr *tb[TCA_PIE_MAX + 1];
152 	unsigned int qlen, dropped = 0;
153 	int err;
154 
155 	if (!opt)
156 		return -EINVAL;
157 
158 	err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, opt, pie_policy,
159 					  NULL);
160 	if (err < 0)
161 		return err;
162 
163 	sch_tree_lock(sch);
164 
165 	/* convert from microseconds to pschedtime */
166 	if (tb[TCA_PIE_TARGET]) {
167 		/* target is in us */
168 		u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
169 
170 		/* convert to pschedtime */
171 		q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
172 	}
173 
174 	/* tupdate is in jiffies */
175 	if (tb[TCA_PIE_TUPDATE])
176 		q->params.tupdate =
177 			usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
178 
179 	if (tb[TCA_PIE_LIMIT]) {
180 		u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
181 
182 		q->params.limit = limit;
183 		sch->limit = limit;
184 	}
185 
186 	if (tb[TCA_PIE_ALPHA])
187 		q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
188 
189 	if (tb[TCA_PIE_BETA])
190 		q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
191 
192 	if (tb[TCA_PIE_ECN])
193 		q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
194 
195 	if (tb[TCA_PIE_BYTEMODE])
196 		q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
197 
198 	if (tb[TCA_PIE_DQ_RATE_ESTIMATOR])
199 		q->params.dq_rate_estimator =
200 				nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]);
201 
202 	/* Drop excess packets if new limit is lower */
203 	qlen = sch->q.qlen;
204 	while (sch->q.qlen > sch->limit) {
205 		struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
206 
207 		dropped += qdisc_pkt_len(skb);
208 		qdisc_qstats_backlog_dec(sch, skb);
209 		rtnl_qdisc_drop(skb, sch);
210 	}
211 	qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
212 
213 	sch_tree_unlock(sch);
214 	return 0;
215 }
216 
217 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
218 			 struct pie_vars *vars, u32 qlen)
219 {
220 	psched_time_t now = psched_get_time();
221 	u32 dtime = 0;
222 
223 	/* If dq_rate_estimator is disabled, calculate qdelay using the
224 	 * packet timestamp.
225 	 */
226 	if (!params->dq_rate_estimator) {
227 		vars->qdelay = now - pie_get_enqueue_time(skb);
228 
229 		if (vars->dq_tstamp != DTIME_INVALID)
230 			dtime = now - vars->dq_tstamp;
231 
232 		vars->dq_tstamp = now;
233 
234 		if (qlen == 0)
235 			vars->qdelay = 0;
236 
237 		if (dtime == 0)
238 			return;
239 
240 		goto burst_allowance_reduction;
241 	}
242 
243 	/* If current queue is about 10 packets or more and dq_count is unset
244 	 * we have enough packets to calculate the drain rate. Save
245 	 * current time as dq_tstamp and start measurement cycle.
246 	 */
247 	if (qlen >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
248 		vars->dq_tstamp = psched_get_time();
249 		vars->dq_count = 0;
250 	}
251 
252 	/* Calculate the average drain rate from this value. If queue length
253 	 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset
254 	 * the dq_count to -1 as we don't have enough packets to calculate the
255 	 * drain rate anymore. The following if block is entered only when we
256 	 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
257 	 * and we calculate the drain rate for the threshold here.  dq_count is
258 	 * in bytes, time difference in psched_time, hence rate is in
259 	 * bytes/psched_time.
260 	 */
261 	if (vars->dq_count != DQCOUNT_INVALID) {
262 		vars->dq_count += skb->len;
263 
264 		if (vars->dq_count >= QUEUE_THRESHOLD) {
265 			u32 count = vars->dq_count << PIE_SCALE;
266 
267 			dtime = now - vars->dq_tstamp;
268 
269 			if (dtime == 0)
270 				return;
271 
272 			count = count / dtime;
273 
274 			if (vars->avg_dq_rate == 0)
275 				vars->avg_dq_rate = count;
276 			else
277 				vars->avg_dq_rate =
278 				    (vars->avg_dq_rate -
279 				     (vars->avg_dq_rate >> 3)) + (count >> 3);
280 
281 			/* If the queue has receded below the threshold, we hold
282 			 * on to the last drain rate calculated, else we reset
283 			 * dq_count to 0 to re-enter the if block when the next
284 			 * packet is dequeued
285 			 */
286 			if (qlen < QUEUE_THRESHOLD) {
287 				vars->dq_count = DQCOUNT_INVALID;
288 			} else {
289 				vars->dq_count = 0;
290 				vars->dq_tstamp = psched_get_time();
291 			}
292 
293 			goto burst_allowance_reduction;
294 		}
295 	}
296 
297 	return;
298 
299 burst_allowance_reduction:
300 	if (vars->burst_time > 0) {
301 		if (vars->burst_time > dtime)
302 			vars->burst_time -= dtime;
303 		else
304 			vars->burst_time = 0;
305 	}
306 }
307 EXPORT_SYMBOL_GPL(pie_process_dequeue);
308 
309 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
310 			       u32 qlen)
311 {
312 	psched_time_t qdelay = 0;	/* in pschedtime */
313 	psched_time_t qdelay_old = 0;	/* in pschedtime */
314 	s64 delta = 0;		/* determines the change in probability */
315 	u64 oldprob;
316 	u64 alpha, beta;
317 	u32 power;
318 	bool update_prob = true;
319 
320 	if (params->dq_rate_estimator) {
321 		qdelay_old = vars->qdelay;
322 		vars->qdelay_old = vars->qdelay;
323 
324 		if (vars->avg_dq_rate > 0)
325 			qdelay = (qlen << PIE_SCALE) / vars->avg_dq_rate;
326 		else
327 			qdelay = 0;
328 	} else {
329 		qdelay = vars->qdelay;
330 		qdelay_old = vars->qdelay_old;
331 	}
332 
333 	/* If qdelay is zero and qlen is not, it means qlen is very small,
334 	 * so we do not update probabilty in this round.
335 	 */
336 	if (qdelay == 0 && qlen != 0)
337 		update_prob = false;
338 
339 	/* In the algorithm, alpha and beta are between 0 and 2 with typical
340 	 * value for alpha as 0.125. In this implementation, we use values 0-32
341 	 * passed from user space to represent this. Also, alpha and beta have
342 	 * unit of HZ and need to be scaled before they can used to update
343 	 * probability. alpha/beta are updated locally below by scaling down
344 	 * by 16 to come to 0-2 range.
345 	 */
346 	alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
347 	beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
348 
349 	/* We scale alpha and beta differently depending on how heavy the
350 	 * congestion is. Please see RFC 8033 for details.
351 	 */
352 	if (vars->prob < MAX_PROB / 10) {
353 		alpha >>= 1;
354 		beta >>= 1;
355 
356 		power = 100;
357 		while (vars->prob < div_u64(MAX_PROB, power) &&
358 		       power <= 1000000) {
359 			alpha >>= 2;
360 			beta >>= 2;
361 			power *= 10;
362 		}
363 	}
364 
365 	/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
366 	delta += alpha * (u64)(qdelay - params->target);
367 	delta += beta * (u64)(qdelay - qdelay_old);
368 
369 	oldprob = vars->prob;
370 
371 	/* to ensure we increase probability in steps of no more than 2% */
372 	if (delta > (s64)(MAX_PROB / (100 / 2)) &&
373 	    vars->prob >= MAX_PROB / 10)
374 		delta = (MAX_PROB / 100) * 2;
375 
376 	/* Non-linear drop:
377 	 * Tune drop probability to increase quickly for high delays(>= 250ms)
378 	 * 250ms is derived through experiments and provides error protection
379 	 */
380 
381 	if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
382 		delta += MAX_PROB / (100 / 2);
383 
384 	vars->prob += delta;
385 
386 	if (delta > 0) {
387 		/* prevent overflow */
388 		if (vars->prob < oldprob) {
389 			vars->prob = MAX_PROB;
390 			/* Prevent normalization error. If probability is at
391 			 * maximum value already, we normalize it here, and
392 			 * skip the check to do a non-linear drop in the next
393 			 * section.
394 			 */
395 			update_prob = false;
396 		}
397 	} else {
398 		/* prevent underflow */
399 		if (vars->prob > oldprob)
400 			vars->prob = 0;
401 	}
402 
403 	/* Non-linear drop in probability: Reduce drop probability quickly if
404 	 * delay is 0 for 2 consecutive Tupdate periods.
405 	 */
406 
407 	if (qdelay == 0 && qdelay_old == 0 && update_prob)
408 		/* Reduce drop probability to 98.4% */
409 		vars->prob -= vars->prob / 64;
410 
411 	vars->qdelay = qdelay;
412 	vars->qlen_old = qlen;
413 
414 	/* We restart the measurement cycle if the following conditions are met
415 	 * 1. If the delay has been low for 2 consecutive Tupdate periods
416 	 * 2. Calculated drop probability is zero
417 	 * 3. If average dq_rate_estimator is enabled, we have atleast one
418 	 *    estimate for the avg_dq_rate ie., is a non-zero value
419 	 */
420 	if ((vars->qdelay < params->target / 2) &&
421 	    (vars->qdelay_old < params->target / 2) &&
422 	    vars->prob == 0 &&
423 	    (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) {
424 		pie_vars_init(vars);
425 	}
426 
427 	if (!params->dq_rate_estimator)
428 		vars->qdelay_old = qdelay;
429 }
430 EXPORT_SYMBOL_GPL(pie_calculate_probability);
431 
432 static void pie_timer(struct timer_list *t)
433 {
434 	struct pie_sched_data *q = from_timer(q, t, adapt_timer);
435 	struct Qdisc *sch = q->sch;
436 	spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
437 
438 	spin_lock(root_lock);
439 	pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog);
440 
441 	/* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
442 	if (q->params.tupdate)
443 		mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
444 	spin_unlock(root_lock);
445 }
446 
447 static int pie_init(struct Qdisc *sch, struct nlattr *opt,
448 		    struct netlink_ext_ack *extack)
449 {
450 	struct pie_sched_data *q = qdisc_priv(sch);
451 
452 	pie_params_init(&q->params);
453 	pie_vars_init(&q->vars);
454 	sch->limit = q->params.limit;
455 
456 	q->sch = sch;
457 	timer_setup(&q->adapt_timer, pie_timer, 0);
458 
459 	if (opt) {
460 		int err = pie_change(sch, opt, extack);
461 
462 		if (err)
463 			return err;
464 	}
465 
466 	mod_timer(&q->adapt_timer, jiffies + HZ / 2);
467 	return 0;
468 }
469 
470 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
471 {
472 	struct pie_sched_data *q = qdisc_priv(sch);
473 	struct nlattr *opts;
474 
475 	opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
476 	if (!opts)
477 		goto nla_put_failure;
478 
479 	/* convert target from pschedtime to us */
480 	if (nla_put_u32(skb, TCA_PIE_TARGET,
481 			((u32)PSCHED_TICKS2NS(q->params.target)) /
482 			NSEC_PER_USEC) ||
483 	    nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
484 	    nla_put_u32(skb, TCA_PIE_TUPDATE,
485 			jiffies_to_usecs(q->params.tupdate)) ||
486 	    nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
487 	    nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
488 	    nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
489 	    nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode) ||
490 	    nla_put_u32(skb, TCA_PIE_DQ_RATE_ESTIMATOR,
491 			q->params.dq_rate_estimator))
492 		goto nla_put_failure;
493 
494 	return nla_nest_end(skb, opts);
495 
496 nla_put_failure:
497 	nla_nest_cancel(skb, opts);
498 	return -1;
499 }
500 
501 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
502 {
503 	struct pie_sched_data *q = qdisc_priv(sch);
504 	struct tc_pie_xstats st = {
505 		.prob		= q->vars.prob,
506 		.delay		= ((u32)PSCHED_TICKS2NS(q->vars.qdelay)) /
507 				   NSEC_PER_USEC,
508 		.packets_in	= q->stats.packets_in,
509 		.overlimit	= q->stats.overlimit,
510 		.maxq		= q->stats.maxq,
511 		.dropped	= q->stats.dropped,
512 		.ecn_mark	= q->stats.ecn_mark,
513 	};
514 
515 	/* avg_dq_rate is only valid if dq_rate_estimator is enabled */
516 	st.dq_rate_estimating = q->params.dq_rate_estimator;
517 
518 	/* unscale and return dq_rate in bytes per sec */
519 	if (q->params.dq_rate_estimator)
520 		st.avg_dq_rate = q->vars.avg_dq_rate *
521 				 (PSCHED_TICKS_PER_SEC) >> PIE_SCALE;
522 
523 	return gnet_stats_copy_app(d, &st, sizeof(st));
524 }
525 
526 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
527 {
528 	struct pie_sched_data *q = qdisc_priv(sch);
529 	struct sk_buff *skb = qdisc_dequeue_head(sch);
530 
531 	if (!skb)
532 		return NULL;
533 
534 	pie_process_dequeue(skb, &q->params, &q->vars, sch->qstats.backlog);
535 	return skb;
536 }
537 
538 static void pie_reset(struct Qdisc *sch)
539 {
540 	struct pie_sched_data *q = qdisc_priv(sch);
541 
542 	qdisc_reset_queue(sch);
543 	pie_vars_init(&q->vars);
544 }
545 
546 static void pie_destroy(struct Qdisc *sch)
547 {
548 	struct pie_sched_data *q = qdisc_priv(sch);
549 
550 	q->params.tupdate = 0;
551 	del_timer_sync(&q->adapt_timer);
552 }
553 
554 static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
555 	.id		= "pie",
556 	.priv_size	= sizeof(struct pie_sched_data),
557 	.enqueue	= pie_qdisc_enqueue,
558 	.dequeue	= pie_qdisc_dequeue,
559 	.peek		= qdisc_peek_dequeued,
560 	.init		= pie_init,
561 	.destroy	= pie_destroy,
562 	.reset		= pie_reset,
563 	.change		= pie_change,
564 	.dump		= pie_dump,
565 	.dump_stats	= pie_dump_stats,
566 	.owner		= THIS_MODULE,
567 };
568 
569 static int __init pie_module_init(void)
570 {
571 	return register_qdisc(&pie_qdisc_ops);
572 }
573 
574 static void __exit pie_module_exit(void)
575 {
576 	unregister_qdisc(&pie_qdisc_ops);
577 }
578 
579 module_init(pie_module_init);
580 module_exit(pie_module_exit);
581 
582 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
583 MODULE_AUTHOR("Vijay Subramanian");
584 MODULE_AUTHOR("Mythili Prabhu");
585 MODULE_LICENSE("GPL");
586