xref: /openbmc/linux/net/sched/sch_pie.c (revision d636fc5d)
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 
pie_drop_early(struct Qdisc * sch,struct pie_params * params,struct pie_vars * vars,u32 backlog,u32 packet_size)33 bool 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 	get_random_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 }
83 EXPORT_SYMBOL_GPL(pie_drop_early);
84 
pie_qdisc_enqueue(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)85 static 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 
121 out:
122 	q->stats.dropped++;
123 	q->vars.accu_prob = 0;
124 	return qdisc_drop(skb, sch, to_free);
125 }
126 
127 static 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 
pie_change(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)138 static 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 	err = nla_parse_nested_deprecated(tb, TCA_PIE_MAX, opt, pie_policy,
147 					  NULL);
148 	if (err < 0)
149 		return err;
150 
151 	sch_tree_lock(sch);
152 
153 	/* convert from microseconds to pschedtime */
154 	if (tb[TCA_PIE_TARGET]) {
155 		/* target is in us */
156 		u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
157 
158 		/* convert to pschedtime */
159 		q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
160 	}
161 
162 	/* tupdate is in jiffies */
163 	if (tb[TCA_PIE_TUPDATE])
164 		q->params.tupdate =
165 			usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
166 
167 	if (tb[TCA_PIE_LIMIT]) {
168 		u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
169 
170 		q->params.limit = limit;
171 		sch->limit = limit;
172 	}
173 
174 	if (tb[TCA_PIE_ALPHA])
175 		q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
176 
177 	if (tb[TCA_PIE_BETA])
178 		q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
179 
180 	if (tb[TCA_PIE_ECN])
181 		q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
182 
183 	if (tb[TCA_PIE_BYTEMODE])
184 		q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
185 
186 	if (tb[TCA_PIE_DQ_RATE_ESTIMATOR])
187 		q->params.dq_rate_estimator =
188 				nla_get_u32(tb[TCA_PIE_DQ_RATE_ESTIMATOR]);
189 
190 	/* Drop excess packets if new limit is lower */
191 	qlen = sch->q.qlen;
192 	while (sch->q.qlen > sch->limit) {
193 		struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
194 
195 		dropped += qdisc_pkt_len(skb);
196 		qdisc_qstats_backlog_dec(sch, skb);
197 		rtnl_qdisc_drop(skb, sch);
198 	}
199 	qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
200 
201 	sch_tree_unlock(sch);
202 	return 0;
203 }
204 
pie_process_dequeue(struct sk_buff * skb,struct pie_params * params,struct pie_vars * vars,u32 backlog)205 void pie_process_dequeue(struct sk_buff *skb, struct pie_params *params,
206 			 struct pie_vars *vars, u32 backlog)
207 {
208 	psched_time_t now = psched_get_time();
209 	u32 dtime = 0;
210 
211 	/* If dq_rate_estimator is disabled, calculate qdelay using the
212 	 * packet timestamp.
213 	 */
214 	if (!params->dq_rate_estimator) {
215 		vars->qdelay = now - pie_get_enqueue_time(skb);
216 
217 		if (vars->dq_tstamp != DTIME_INVALID)
218 			dtime = now - vars->dq_tstamp;
219 
220 		vars->dq_tstamp = now;
221 
222 		if (backlog == 0)
223 			vars->qdelay = 0;
224 
225 		if (dtime == 0)
226 			return;
227 
228 		goto burst_allowance_reduction;
229 	}
230 
231 	/* If current queue is about 10 packets or more and dq_count is unset
232 	 * we have enough packets to calculate the drain rate. Save
233 	 * current time as dq_tstamp and start measurement cycle.
234 	 */
235 	if (backlog >= QUEUE_THRESHOLD && vars->dq_count == DQCOUNT_INVALID) {
236 		vars->dq_tstamp = psched_get_time();
237 		vars->dq_count = 0;
238 	}
239 
240 	/* Calculate the average drain rate from this value. If queue length
241 	 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes, reset
242 	 * the dq_count to -1 as we don't have enough packets to calculate the
243 	 * drain rate anymore. The following if block is entered only when we
244 	 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
245 	 * and we calculate the drain rate for the threshold here.  dq_count is
246 	 * in bytes, time difference in psched_time, hence rate is in
247 	 * bytes/psched_time.
248 	 */
249 	if (vars->dq_count != DQCOUNT_INVALID) {
250 		vars->dq_count += skb->len;
251 
252 		if (vars->dq_count >= QUEUE_THRESHOLD) {
253 			u32 count = vars->dq_count << PIE_SCALE;
254 
255 			dtime = now - vars->dq_tstamp;
256 
257 			if (dtime == 0)
258 				return;
259 
260 			count = count / dtime;
261 
262 			if (vars->avg_dq_rate == 0)
263 				vars->avg_dq_rate = count;
264 			else
265 				vars->avg_dq_rate =
266 				    (vars->avg_dq_rate -
267 				     (vars->avg_dq_rate >> 3)) + (count >> 3);
268 
269 			/* If the queue has receded below the threshold, we hold
270 			 * on to the last drain rate calculated, else we reset
271 			 * dq_count to 0 to re-enter the if block when the next
272 			 * packet is dequeued
273 			 */
274 			if (backlog < QUEUE_THRESHOLD) {
275 				vars->dq_count = DQCOUNT_INVALID;
276 			} else {
277 				vars->dq_count = 0;
278 				vars->dq_tstamp = psched_get_time();
279 			}
280 
281 			goto burst_allowance_reduction;
282 		}
283 	}
284 
285 	return;
286 
287 burst_allowance_reduction:
288 	if (vars->burst_time > 0) {
289 		if (vars->burst_time > dtime)
290 			vars->burst_time -= dtime;
291 		else
292 			vars->burst_time = 0;
293 	}
294 }
295 EXPORT_SYMBOL_GPL(pie_process_dequeue);
296 
pie_calculate_probability(struct pie_params * params,struct pie_vars * vars,u32 backlog)297 void pie_calculate_probability(struct pie_params *params, struct pie_vars *vars,
298 			       u32 backlog)
299 {
300 	psched_time_t qdelay = 0;	/* in pschedtime */
301 	psched_time_t qdelay_old = 0;	/* in pschedtime */
302 	s64 delta = 0;		/* determines the change in probability */
303 	u64 oldprob;
304 	u64 alpha, beta;
305 	u32 power;
306 	bool update_prob = true;
307 
308 	if (params->dq_rate_estimator) {
309 		qdelay_old = vars->qdelay;
310 		vars->qdelay_old = vars->qdelay;
311 
312 		if (vars->avg_dq_rate > 0)
313 			qdelay = (backlog << PIE_SCALE) / vars->avg_dq_rate;
314 		else
315 			qdelay = 0;
316 	} else {
317 		qdelay = vars->qdelay;
318 		qdelay_old = vars->qdelay_old;
319 	}
320 
321 	/* If qdelay is zero and backlog is not, it means backlog is very small,
322 	 * so we do not update probability in this round.
323 	 */
324 	if (qdelay == 0 && backlog != 0)
325 		update_prob = false;
326 
327 	/* In the algorithm, alpha and beta are between 0 and 2 with typical
328 	 * value for alpha as 0.125. In this implementation, we use values 0-32
329 	 * passed from user space to represent this. Also, alpha and beta have
330 	 * unit of HZ and need to be scaled before they can used to update
331 	 * probability. alpha/beta are updated locally below by scaling down
332 	 * by 16 to come to 0-2 range.
333 	 */
334 	alpha = ((u64)params->alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
335 	beta = ((u64)params->beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
336 
337 	/* We scale alpha and beta differently depending on how heavy the
338 	 * congestion is. Please see RFC 8033 for details.
339 	 */
340 	if (vars->prob < MAX_PROB / 10) {
341 		alpha >>= 1;
342 		beta >>= 1;
343 
344 		power = 100;
345 		while (vars->prob < div_u64(MAX_PROB, power) &&
346 		       power <= 1000000) {
347 			alpha >>= 2;
348 			beta >>= 2;
349 			power *= 10;
350 		}
351 	}
352 
353 	/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
354 	delta += alpha * (qdelay - params->target);
355 	delta += beta * (qdelay - qdelay_old);
356 
357 	oldprob = vars->prob;
358 
359 	/* to ensure we increase probability in steps of no more than 2% */
360 	if (delta > (s64)(MAX_PROB / (100 / 2)) &&
361 	    vars->prob >= MAX_PROB / 10)
362 		delta = (MAX_PROB / 100) * 2;
363 
364 	/* Non-linear drop:
365 	 * Tune drop probability to increase quickly for high delays(>= 250ms)
366 	 * 250ms is derived through experiments and provides error protection
367 	 */
368 
369 	if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
370 		delta += MAX_PROB / (100 / 2);
371 
372 	vars->prob += delta;
373 
374 	if (delta > 0) {
375 		/* prevent overflow */
376 		if (vars->prob < oldprob) {
377 			vars->prob = MAX_PROB;
378 			/* Prevent normalization error. If probability is at
379 			 * maximum value already, we normalize it here, and
380 			 * skip the check to do a non-linear drop in the next
381 			 * section.
382 			 */
383 			update_prob = false;
384 		}
385 	} else {
386 		/* prevent underflow */
387 		if (vars->prob > oldprob)
388 			vars->prob = 0;
389 	}
390 
391 	/* Non-linear drop in probability: Reduce drop probability quickly if
392 	 * delay is 0 for 2 consecutive Tupdate periods.
393 	 */
394 
395 	if (qdelay == 0 && qdelay_old == 0 && update_prob)
396 		/* Reduce drop probability to 98.4% */
397 		vars->prob -= vars->prob / 64;
398 
399 	vars->qdelay = qdelay;
400 	vars->backlog_old = backlog;
401 
402 	/* We restart the measurement cycle if the following conditions are met
403 	 * 1. If the delay has been low for 2 consecutive Tupdate periods
404 	 * 2. Calculated drop probability is zero
405 	 * 3. If average dq_rate_estimator is enabled, we have at least one
406 	 *    estimate for the avg_dq_rate ie., is a non-zero value
407 	 */
408 	if ((vars->qdelay < params->target / 2) &&
409 	    (vars->qdelay_old < params->target / 2) &&
410 	    vars->prob == 0 &&
411 	    (!params->dq_rate_estimator || vars->avg_dq_rate > 0)) {
412 		pie_vars_init(vars);
413 	}
414 
415 	if (!params->dq_rate_estimator)
416 		vars->qdelay_old = qdelay;
417 }
418 EXPORT_SYMBOL_GPL(pie_calculate_probability);
419 
pie_timer(struct timer_list * t)420 static void pie_timer(struct timer_list *t)
421 {
422 	struct pie_sched_data *q = from_timer(q, t, adapt_timer);
423 	struct Qdisc *sch = q->sch;
424 	spinlock_t *root_lock;
425 
426 	rcu_read_lock();
427 	root_lock = qdisc_lock(qdisc_root_sleeping(sch));
428 	spin_lock(root_lock);
429 	pie_calculate_probability(&q->params, &q->vars, sch->qstats.backlog);
430 
431 	/* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
432 	if (q->params.tupdate)
433 		mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
434 	spin_unlock(root_lock);
435 	rcu_read_unlock();
436 }
437 
pie_init(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)438 static 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 
pie_dump(struct Qdisc * sch,struct sk_buff * skb)461 static 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 
487 nla_put_failure:
488 	nla_nest_cancel(skb, opts);
489 	return -1;
490 }
491 
pie_dump_stats(struct Qdisc * sch,struct gnet_dump * d)492 static 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 
pie_qdisc_dequeue(struct Qdisc * sch)517 static 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 
pie_reset(struct Qdisc * sch)529 static 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 
pie_destroy(struct Qdisc * sch)537 static 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 
545 static 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 
pie_module_init(void)560 static int __init pie_module_init(void)
561 {
562 	return register_qdisc(&pie_qdisc_ops);
563 }
564 
pie_module_exit(void)565 static void __exit pie_module_exit(void)
566 {
567 	unregister_qdisc(&pie_qdisc_ops);
568 }
569 
570 module_init(pie_module_init);
571 module_exit(pie_module_exit);
572 
573 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
574 MODULE_AUTHOR("Vijay Subramanian");
575 MODULE_AUTHOR("Mythili Prabhu");
576 MODULE_LICENSE("GPL");
577