sch_pie.c 15.5 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566
/* Copyright (C) 2013 Cisco Systems, Inc, 2013.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * Author: Vijay Subramanian <vijaynsu@cisco.com>
 * Author: Mythili Prabhu <mysuryan@cisco.com>
 *
 * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
 * University of Oslo, Norway.
 *
 * References:
 * IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00
 * IEEE  Conference on High Performance Switching and Routing 2013 :
 * "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem"
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/skbuff.h>
#include <net/pkt_sched.h>
#include <net/inet_ecn.h>

#define QUEUE_THRESHOLD 10000
#define DQCOUNT_INVALID -1
#define MAX_PROB  0xffffffff
#define PIE_SCALE 8

/* parameters used */
struct pie_params {
	psched_time_t target;	/* user specified target delay in pschedtime */
	u32 tupdate;		/* timer frequency (in jiffies) */
	u32 limit;		/* number of packets that can be enqueued */
	u32 alpha;		/* alpha and beta are between 0 and 32 */
	u32 beta;		/* and are used for shift relative to 1 */
	bool ecn;		/* true if ecn is enabled */
	bool bytemode;		/* to scale drop early prob based on pkt size */
};

/* variables used */
struct pie_vars {
	u32 prob;		/* probability but scaled by u32 limit. */
	psched_time_t burst_time;
	psched_time_t qdelay;
	psched_time_t qdelay_old;
	u64 dq_count;		/* measured in bytes */
	psched_time_t dq_tstamp;	/* drain rate */
	u32 avg_dq_rate;	/* bytes per pschedtime tick,scaled */
	u32 qlen_old;		/* in bytes */
};

/* statistics gathering */
struct pie_stats {
	u32 packets_in;		/* total number of packets enqueued */
	u32 dropped;		/* packets dropped due to pie_action */
	u32 overlimit;		/* dropped due to lack of space in queue */
	u32 maxq;		/* maximum queue size */
	u32 ecn_mark;		/* packets marked with ECN */
};

/* private data for the Qdisc */
struct pie_sched_data {
	struct pie_params params;
	struct pie_vars vars;
	struct pie_stats stats;
	struct timer_list adapt_timer;
};

static void pie_params_init(struct pie_params *params)
{
	params->alpha = 2;
	params->beta = 20;
	params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC);	/* 30 ms */
	params->limit = 1000;	/* default of 1000 packets */
	params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC);	/* 20 ms */
	params->ecn = false;
	params->bytemode = false;
}

static void pie_vars_init(struct pie_vars *vars)
{
	vars->dq_count = DQCOUNT_INVALID;
	vars->avg_dq_rate = 0;
	/* default of 100 ms in pschedtime */
	vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC);
}

static bool drop_early(struct Qdisc *sch, u32 packet_size)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	u32 rnd;
	u32 local_prob = q->vars.prob;
	u32 mtu = psched_mtu(qdisc_dev(sch));

	/* If there is still burst allowance left skip random early drop */
	if (q->vars.burst_time > 0)
		return false;

	/* If current delay is less than half of target, and
	 * if drop prob is low already, disable early_drop
	 */
	if ((q->vars.qdelay < q->params.target / 2)
	    && (q->vars.prob < MAX_PROB / 5))
		return false;

	/* If we have fewer than 2 mtu-sized packets, disable drop_early,
	 * similar to min_th in RED
	 */
	if (sch->qstats.backlog < 2 * mtu)
		return false;

	/* If bytemode is turned on, use packet size to compute new
	 * probablity. Smaller packets will have lower drop prob in this case
	 */
	if (q->params.bytemode && packet_size <= mtu)
		local_prob = (local_prob / mtu) * packet_size;
	else
		local_prob = q->vars.prob;

	rnd = prandom_u32();
	if (rnd < local_prob)
		return true;

	return false;
}

static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	bool enqueue = false;

	if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
		q->stats.overlimit++;
		goto out;
	}

	if (!drop_early(sch, skb->len)) {
		enqueue = true;
	} else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
		   INET_ECN_set_ce(skb)) {
		/* If packet is ecn capable, mark it if drop probability
		 * is lower than 10%, else drop it.
		 */
		q->stats.ecn_mark++;
		enqueue = true;
	}

	/* we can enqueue the packet */
	if (enqueue) {
		q->stats.packets_in++;
		if (qdisc_qlen(sch) > q->stats.maxq)
			q->stats.maxq = qdisc_qlen(sch);

		return qdisc_enqueue_tail(skb, sch);
	}

out:
	q->stats.dropped++;
	return qdisc_drop(skb, sch);
}

static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
	[TCA_PIE_TARGET] = {.type = NLA_U32},
	[TCA_PIE_LIMIT] = {.type = NLA_U32},
	[TCA_PIE_TUPDATE] = {.type = NLA_U32},
	[TCA_PIE_ALPHA] = {.type = NLA_U32},
	[TCA_PIE_BETA] = {.type = NLA_U32},
	[TCA_PIE_ECN] = {.type = NLA_U32},
	[TCA_PIE_BYTEMODE] = {.type = NLA_U32},
};

static int pie_change(struct Qdisc *sch, struct nlattr *opt)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	struct nlattr *tb[TCA_PIE_MAX + 1];
	unsigned int qlen;
	int err;

	if (!opt)
		return -EINVAL;

	err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy);
	if (err < 0)
		return err;

	sch_tree_lock(sch);

	/* convert from microseconds to pschedtime */
	if (tb[TCA_PIE_TARGET]) {
		/* target is in us */
		u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);

		/* convert to pschedtime */
		q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
	}

	/* tupdate is in jiffies */
	if (tb[TCA_PIE_TUPDATE])
		q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));

	if (tb[TCA_PIE_LIMIT]) {
		u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);

		q->params.limit = limit;
		sch->limit = limit;
	}

	if (tb[TCA_PIE_ALPHA])
		q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);

	if (tb[TCA_PIE_BETA])
		q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);

	if (tb[TCA_PIE_ECN])
		q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);

	if (tb[TCA_PIE_BYTEMODE])
		q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);

	/* Drop excess packets if new limit is lower */
	qlen = sch->q.qlen;
	while (sch->q.qlen > sch->limit) {
		struct sk_buff *skb = __skb_dequeue(&sch->q);

		sch->qstats.backlog -= qdisc_pkt_len(skb);
		qdisc_drop(skb, sch);
	}
	qdisc_tree_decrease_qlen(sch, qlen - sch->q.qlen);

	sch_tree_unlock(sch);
	return 0;
}

static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
{

	struct pie_sched_data *q = qdisc_priv(sch);
	int qlen = sch->qstats.backlog;	/* current queue size in bytes */

	/* If current queue is about 10 packets or more and dq_count is unset
	 * we have enough packets to calculate the drain rate. Save
	 * current time as dq_tstamp and start measurement cycle.
	 */
	if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
		q->vars.dq_tstamp = psched_get_time();
		q->vars.dq_count = 0;
	}

	/* Calculate the average drain rate from this value.  If queue length
	 * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
	 * the dq_count to -1 as we don't have enough packets to calculate the
	 * drain rate anymore The following if block is entered only when we
	 * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
	 * and we calculate the drain rate for the threshold here.  dq_count is
	 * in bytes, time difference in psched_time, hence rate is in
	 * bytes/psched_time.
	 */
	if (q->vars.dq_count != DQCOUNT_INVALID) {
		q->vars.dq_count += skb->len;

		if (q->vars.dq_count >= QUEUE_THRESHOLD) {
			psched_time_t now = psched_get_time();
			u32 dtime = now - q->vars.dq_tstamp;
			u32 count = q->vars.dq_count << PIE_SCALE;

			if (dtime == 0)
				return;

			count = count / dtime;

			if (q->vars.avg_dq_rate == 0)
				q->vars.avg_dq_rate = count;
			else
				q->vars.avg_dq_rate =
				    (q->vars.avg_dq_rate -
				     (q->vars.avg_dq_rate >> 3)) + (count >> 3);

			/* If the queue has receded below the threshold, we hold
			 * on to the last drain rate calculated, else we reset
			 * dq_count to 0 to re-enter the if block when the next
			 * packet is dequeued
			 */
			if (qlen < QUEUE_THRESHOLD)
				q->vars.dq_count = DQCOUNT_INVALID;
			else {
				q->vars.dq_count = 0;
				q->vars.dq_tstamp = psched_get_time();
			}

			if (q->vars.burst_time > 0) {
				if (q->vars.burst_time > dtime)
					q->vars.burst_time -= dtime;
				else
					q->vars.burst_time = 0;
			}
		}
	}
}

static void calculate_probability(struct Qdisc *sch)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	u32 qlen = sch->qstats.backlog;	/* queue size in bytes */
	psched_time_t qdelay = 0;	/* in pschedtime */
	psched_time_t qdelay_old = q->vars.qdelay;	/* in pschedtime */
	s32 delta = 0;		/* determines the change in probability */
	u32 oldprob;
	u32 alpha, beta;
	bool update_prob = true;

	q->vars.qdelay_old = q->vars.qdelay;

	if (q->vars.avg_dq_rate > 0)
		qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
	else
		qdelay = 0;

	/* If qdelay is zero and qlen is not, it means qlen is very small, less
	 * than dequeue_rate, so we do not update probabilty in this round
	 */
	if (qdelay == 0 && qlen != 0)
		update_prob = false;

	/* In the algorithm, alpha and beta are between 0 and 2 with typical
	 * value for alpha as 0.125. In this implementation, we use values 0-32
	 * passed from user space to represent this. Also, alpha and beta have
	 * unit of HZ and need to be scaled before they can used to update
	 * probability. alpha/beta are updated locally below by 1) scaling them
	 * appropriately 2) scaling down by 16 to come to 0-2 range.
	 * Please see paper for details.
	 *
	 * We scale alpha and beta differently depending on whether we are in
	 * light, medium or high dropping mode.
	 */
	if (q->vars.prob < MAX_PROB / 100) {
		alpha =
		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
		beta =
		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
	} else if (q->vars.prob < MAX_PROB / 10) {
		alpha =
		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
		beta =
		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
	} else {
		alpha =
		    (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
		beta =
		    (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
	}

	/* alpha and beta should be between 0 and 32, in multiples of 1/16 */
	delta += alpha * ((qdelay - q->params.target));
	delta += beta * ((qdelay - qdelay_old));

	oldprob = q->vars.prob;

	/* to ensure we increase probability in steps of no more than 2% */
	if (delta > (s32) (MAX_PROB / (100 / 2)) &&
	    q->vars.prob >= MAX_PROB / 10)
		delta = (MAX_PROB / 100) * 2;

	/* Non-linear drop:
	 * Tune drop probability to increase quickly for high delays(>= 250ms)
	 * 250ms is derived through experiments and provides error protection
	 */

	if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
		delta += MAX_PROB / (100 / 2);

	q->vars.prob += delta;

	if (delta > 0) {
		/* prevent overflow */
		if (q->vars.prob < oldprob) {
			q->vars.prob = MAX_PROB;
			/* Prevent normalization error. If probability is at
			 * maximum value already, we normalize it here, and
			 * skip the check to do a non-linear drop in the next
			 * section.
			 */
			update_prob = false;
		}
	} else {
		/* prevent underflow */
		if (q->vars.prob > oldprob)
			q->vars.prob = 0;
	}

	/* Non-linear drop in probability: Reduce drop probability quickly if
	 * delay is 0 for 2 consecutive Tupdate periods.
	 */

	if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
		q->vars.prob = (q->vars.prob * 98) / 100;

	q->vars.qdelay = qdelay;
	q->vars.qlen_old = qlen;

	/* We restart the measurement cycle if the following conditions are met
	 * 1. If the delay has been low for 2 consecutive Tupdate periods
	 * 2. Calculated drop probability is zero
	 * 3. We have atleast one estimate for the avg_dq_rate ie.,
	 *    is a non-zero value
	 */
	if ((q->vars.qdelay < q->params.target / 2) &&
	    (q->vars.qdelay_old < q->params.target / 2) &&
	    (q->vars.prob == 0) &&
	    (q->vars.avg_dq_rate > 0))
		pie_vars_init(&q->vars);
}

static void pie_timer(unsigned long arg)
{
	struct Qdisc *sch = (struct Qdisc *)arg;
	struct pie_sched_data *q = qdisc_priv(sch);
	spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));

	spin_lock(root_lock);
	calculate_probability(sch);

	/* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
	if (q->params.tupdate)
		mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
	spin_unlock(root_lock);

}

static int pie_init(struct Qdisc *sch, struct nlattr *opt)
{
	struct pie_sched_data *q = qdisc_priv(sch);

	pie_params_init(&q->params);
	pie_vars_init(&q->vars);
	sch->limit = q->params.limit;

	setup_timer(&q->adapt_timer, pie_timer, (unsigned long)sch);
	mod_timer(&q->adapt_timer, jiffies + HZ / 2);

	if (opt) {
		int err = pie_change(sch, opt);

		if (err)
			return err;
	}

	return 0;
}

static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	struct nlattr *opts;

	opts = nla_nest_start(skb, TCA_OPTIONS);
	if (opts == NULL)
		goto nla_put_failure;

	/* convert target from pschedtime to us */
	if (nla_put_u32(skb, TCA_PIE_TARGET,
			((u32) PSCHED_TICKS2NS(q->params.target)) /
			NSEC_PER_USEC) ||
	    nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
	    nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
	    nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
	    nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
	    nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
	    nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
		goto nla_put_failure;

	return nla_nest_end(skb, opts);

nla_put_failure:
	nla_nest_cancel(skb, opts);
	return -1;

}

static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	struct tc_pie_xstats st = {
		.prob		= q->vars.prob,
		.delay		= ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
				   NSEC_PER_USEC,
		/* unscale and return dq_rate in bytes per sec */
		.avg_dq_rate	= q->vars.avg_dq_rate *
				  (PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
		.packets_in	= q->stats.packets_in,
		.overlimit	= q->stats.overlimit,
		.maxq		= q->stats.maxq,
		.dropped	= q->stats.dropped,
		.ecn_mark	= q->stats.ecn_mark,
	};

	return gnet_stats_copy_app(d, &st, sizeof(st));
}

static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
{
	struct sk_buff *skb;
	skb = __qdisc_dequeue_head(sch, &sch->q);

	if (!skb)
		return NULL;

	pie_process_dequeue(sch, skb);
	return skb;
}

static void pie_reset(struct Qdisc *sch)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	qdisc_reset_queue(sch);
	pie_vars_init(&q->vars);
}

static void pie_destroy(struct Qdisc *sch)
{
	struct pie_sched_data *q = qdisc_priv(sch);
	q->params.tupdate = 0;
	del_timer_sync(&q->adapt_timer);
}

static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
	.id = "pie",
	.priv_size	= sizeof(struct pie_sched_data),
	.enqueue	= pie_qdisc_enqueue,
	.dequeue	= pie_qdisc_dequeue,
	.peek		= qdisc_peek_dequeued,
	.init		= pie_init,
	.destroy	= pie_destroy,
	.reset		= pie_reset,
	.change		= pie_change,
	.dump		= pie_dump,
	.dump_stats	= pie_dump_stats,
	.owner		= THIS_MODULE,
};

static int __init pie_module_init(void)
{
	return register_qdisc(&pie_qdisc_ops);
}

static void __exit pie_module_exit(void)
{
	unregister_qdisc(&pie_qdisc_ops);
}

module_init(pie_module_init);
module_exit(pie_module_exit);

MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
MODULE_AUTHOR("Vijay Subramanian");
MODULE_AUTHOR("Mythili Prabhu");
MODULE_LICENSE("GPL");