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Linux/net/sched/sch_pie.c

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  1 /* Copyright (C) 2013 Cisco Systems, Inc, 2013.
  2  *
  3  * This program is free software; you can redistribute it and/or
  4  * modify it under the terms of the GNU General Public License
  5  * as published by the Free Software Foundation; either version 2
  6  * of the License.
  7  *
  8  * This program is distributed in the hope that it will be useful,
  9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 11  * GNU General Public License for more details.
 12  *
 13  * Author: Vijay Subramanian <vijaynsu@cisco.com>
 14  * Author: Mythili Prabhu <mysuryan@cisco.com>
 15  *
 16  * ECN support is added by Naeem Khademi <naeemk@ifi.uio.no>
 17  * University of Oslo, Norway.
 18  *
 19  * References:
 20  * IETF draft submission: http://tools.ietf.org/html/draft-pan-aqm-pie-00
 21  * IEEE  Conference on High Performance Switching and Routing 2013 :
 22  * "PIE: A * Lightweight Control Scheme to Address the Bufferbloat Problem"
 23  */
 24 
 25 #include <linux/module.h>
 26 #include <linux/slab.h>
 27 #include <linux/types.h>
 28 #include <linux/kernel.h>
 29 #include <linux/errno.h>
 30 #include <linux/skbuff.h>
 31 #include <net/pkt_sched.h>
 32 #include <net/inet_ecn.h>
 33 
 34 #define QUEUE_THRESHOLD 10000
 35 #define DQCOUNT_INVALID -1
 36 #define MAX_PROB  0xffffffff
 37 #define PIE_SCALE 8
 38 
 39 /* parameters used */
 40 struct pie_params {
 41         psched_time_t target;   /* user specified target delay in pschedtime */
 42         u32 tupdate;            /* timer frequency (in jiffies) */
 43         u32 limit;              /* number of packets that can be enqueued */
 44         u32 alpha;              /* alpha and beta are between 0 and 32 */
 45         u32 beta;               /* and are used for shift relative to 1 */
 46         bool ecn;               /* true if ecn is enabled */
 47         bool bytemode;          /* to scale drop early prob based on pkt size */
 48 };
 49 
 50 /* variables used */
 51 struct pie_vars {
 52         u32 prob;               /* probability but scaled by u32 limit. */
 53         psched_time_t burst_time;
 54         psched_time_t qdelay;
 55         psched_time_t qdelay_old;
 56         u64 dq_count;           /* measured in bytes */
 57         psched_time_t dq_tstamp;        /* drain rate */
 58         u32 avg_dq_rate;        /* bytes per pschedtime tick,scaled */
 59         u32 qlen_old;           /* in bytes */
 60 };
 61 
 62 /* statistics gathering */
 63 struct pie_stats {
 64         u32 packets_in;         /* total number of packets enqueued */
 65         u32 dropped;            /* packets dropped due to pie_action */
 66         u32 overlimit;          /* dropped due to lack of space in queue */
 67         u32 maxq;               /* maximum queue size */
 68         u32 ecn_mark;           /* packets marked with ECN */
 69 };
 70 
 71 /* private data for the Qdisc */
 72 struct pie_sched_data {
 73         struct pie_params params;
 74         struct pie_vars vars;
 75         struct pie_stats stats;
 76         struct timer_list adapt_timer;
 77         struct Qdisc *sch;
 78 };
 79 
 80 static void pie_params_init(struct pie_params *params)
 81 {
 82         params->alpha = 2;
 83         params->beta = 20;
 84         params->tupdate = usecs_to_jiffies(30 * USEC_PER_MSEC); /* 30 ms */
 85         params->limit = 1000;   /* default of 1000 packets */
 86         params->target = PSCHED_NS2TICKS(20 * NSEC_PER_MSEC);   /* 20 ms */
 87         params->ecn = false;
 88         params->bytemode = false;
 89 }
 90 
 91 static void pie_vars_init(struct pie_vars *vars)
 92 {
 93         vars->dq_count = DQCOUNT_INVALID;
 94         vars->avg_dq_rate = 0;
 95         /* default of 100 ms in pschedtime */
 96         vars->burst_time = PSCHED_NS2TICKS(100 * NSEC_PER_MSEC);
 97 }
 98 
 99 static bool drop_early(struct Qdisc *sch, u32 packet_size)
100 {
101         struct pie_sched_data *q = qdisc_priv(sch);
102         u32 rnd;
103         u32 local_prob = q->vars.prob;
104         u32 mtu = psched_mtu(qdisc_dev(sch));
105 
106         /* If there is still burst allowance left skip random early drop */
107         if (q->vars.burst_time > 0)
108                 return false;
109 
110         /* If current delay is less than half of target, and
111          * if drop prob is low already, disable early_drop
112          */
113         if ((q->vars.qdelay < q->params.target / 2)
114             && (q->vars.prob < MAX_PROB / 5))
115                 return false;
116 
117         /* If we have fewer than 2 mtu-sized packets, disable drop_early,
118          * similar to min_th in RED
119          */
120         if (sch->qstats.backlog < 2 * mtu)
121                 return false;
122 
123         /* If bytemode is turned on, use packet size to compute new
124          * probablity. Smaller packets will have lower drop prob in this case
125          */
126         if (q->params.bytemode && packet_size <= mtu)
127                 local_prob = (local_prob / mtu) * packet_size;
128         else
129                 local_prob = q->vars.prob;
130 
131         rnd = prandom_u32();
132         if (rnd < local_prob)
133                 return true;
134 
135         return false;
136 }
137 
138 static int pie_qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch,
139                              struct sk_buff **to_free)
140 {
141         struct pie_sched_data *q = qdisc_priv(sch);
142         bool enqueue = false;
143 
144         if (unlikely(qdisc_qlen(sch) >= sch->limit)) {
145                 q->stats.overlimit++;
146                 goto out;
147         }
148 
149         if (!drop_early(sch, skb->len)) {
150                 enqueue = true;
151         } else if (q->params.ecn && (q->vars.prob <= MAX_PROB / 10) &&
152                    INET_ECN_set_ce(skb)) {
153                 /* If packet is ecn capable, mark it if drop probability
154                  * is lower than 10%, else drop it.
155                  */
156                 q->stats.ecn_mark++;
157                 enqueue = true;
158         }
159 
160         /* we can enqueue the packet */
161         if (enqueue) {
162                 q->stats.packets_in++;
163                 if (qdisc_qlen(sch) > q->stats.maxq)
164                         q->stats.maxq = qdisc_qlen(sch);
165 
166                 return qdisc_enqueue_tail(skb, sch);
167         }
168 
169 out:
170         q->stats.dropped++;
171         return qdisc_drop(skb, sch, to_free);
172 }
173 
174 static const struct nla_policy pie_policy[TCA_PIE_MAX + 1] = {
175         [TCA_PIE_TARGET] = {.type = NLA_U32},
176         [TCA_PIE_LIMIT] = {.type = NLA_U32},
177         [TCA_PIE_TUPDATE] = {.type = NLA_U32},
178         [TCA_PIE_ALPHA] = {.type = NLA_U32},
179         [TCA_PIE_BETA] = {.type = NLA_U32},
180         [TCA_PIE_ECN] = {.type = NLA_U32},
181         [TCA_PIE_BYTEMODE] = {.type = NLA_U32},
182 };
183 
184 static int pie_change(struct Qdisc *sch, struct nlattr *opt,
185                       struct netlink_ext_ack *extack)
186 {
187         struct pie_sched_data *q = qdisc_priv(sch);
188         struct nlattr *tb[TCA_PIE_MAX + 1];
189         unsigned int qlen, dropped = 0;
190         int err;
191 
192         if (!opt)
193                 return -EINVAL;
194 
195         err = nla_parse_nested(tb, TCA_PIE_MAX, opt, pie_policy, NULL);
196         if (err < 0)
197                 return err;
198 
199         sch_tree_lock(sch);
200 
201         /* convert from microseconds to pschedtime */
202         if (tb[TCA_PIE_TARGET]) {
203                 /* target is in us */
204                 u32 target = nla_get_u32(tb[TCA_PIE_TARGET]);
205 
206                 /* convert to pschedtime */
207                 q->params.target = PSCHED_NS2TICKS((u64)target * NSEC_PER_USEC);
208         }
209 
210         /* tupdate is in jiffies */
211         if (tb[TCA_PIE_TUPDATE])
212                 q->params.tupdate = usecs_to_jiffies(nla_get_u32(tb[TCA_PIE_TUPDATE]));
213 
214         if (tb[TCA_PIE_LIMIT]) {
215                 u32 limit = nla_get_u32(tb[TCA_PIE_LIMIT]);
216 
217                 q->params.limit = limit;
218                 sch->limit = limit;
219         }
220 
221         if (tb[TCA_PIE_ALPHA])
222                 q->params.alpha = nla_get_u32(tb[TCA_PIE_ALPHA]);
223 
224         if (tb[TCA_PIE_BETA])
225                 q->params.beta = nla_get_u32(tb[TCA_PIE_BETA]);
226 
227         if (tb[TCA_PIE_ECN])
228                 q->params.ecn = nla_get_u32(tb[TCA_PIE_ECN]);
229 
230         if (tb[TCA_PIE_BYTEMODE])
231                 q->params.bytemode = nla_get_u32(tb[TCA_PIE_BYTEMODE]);
232 
233         /* Drop excess packets if new limit is lower */
234         qlen = sch->q.qlen;
235         while (sch->q.qlen > sch->limit) {
236                 struct sk_buff *skb = __qdisc_dequeue_head(&sch->q);
237 
238                 dropped += qdisc_pkt_len(skb);
239                 qdisc_qstats_backlog_dec(sch, skb);
240                 rtnl_qdisc_drop(skb, sch);
241         }
242         qdisc_tree_reduce_backlog(sch, qlen - sch->q.qlen, dropped);
243 
244         sch_tree_unlock(sch);
245         return 0;
246 }
247 
248 static void pie_process_dequeue(struct Qdisc *sch, struct sk_buff *skb)
249 {
250 
251         struct pie_sched_data *q = qdisc_priv(sch);
252         int qlen = sch->qstats.backlog; /* current queue size in bytes */
253 
254         /* If current queue is about 10 packets or more and dq_count is unset
255          * we have enough packets to calculate the drain rate. Save
256          * current time as dq_tstamp and start measurement cycle.
257          */
258         if (qlen >= QUEUE_THRESHOLD && q->vars.dq_count == DQCOUNT_INVALID) {
259                 q->vars.dq_tstamp = psched_get_time();
260                 q->vars.dq_count = 0;
261         }
262 
263         /* Calculate the average drain rate from this value.  If queue length
264          * has receded to a small value viz., <= QUEUE_THRESHOLD bytes,reset
265          * the dq_count to -1 as we don't have enough packets to calculate the
266          * drain rate anymore The following if block is entered only when we
267          * have a substantial queue built up (QUEUE_THRESHOLD bytes or more)
268          * and we calculate the drain rate for the threshold here.  dq_count is
269          * in bytes, time difference in psched_time, hence rate is in
270          * bytes/psched_time.
271          */
272         if (q->vars.dq_count != DQCOUNT_INVALID) {
273                 q->vars.dq_count += skb->len;
274 
275                 if (q->vars.dq_count >= QUEUE_THRESHOLD) {
276                         psched_time_t now = psched_get_time();
277                         u32 dtime = now - q->vars.dq_tstamp;
278                         u32 count = q->vars.dq_count << PIE_SCALE;
279 
280                         if (dtime == 0)
281                                 return;
282 
283                         count = count / dtime;
284 
285                         if (q->vars.avg_dq_rate == 0)
286                                 q->vars.avg_dq_rate = count;
287                         else
288                                 q->vars.avg_dq_rate =
289                                     (q->vars.avg_dq_rate -
290                                      (q->vars.avg_dq_rate >> 3)) + (count >> 3);
291 
292                         /* If the queue has receded below the threshold, we hold
293                          * on to the last drain rate calculated, else we reset
294                          * dq_count to 0 to re-enter the if block when the next
295                          * packet is dequeued
296                          */
297                         if (qlen < QUEUE_THRESHOLD)
298                                 q->vars.dq_count = DQCOUNT_INVALID;
299                         else {
300                                 q->vars.dq_count = 0;
301                                 q->vars.dq_tstamp = psched_get_time();
302                         }
303 
304                         if (q->vars.burst_time > 0) {
305                                 if (q->vars.burst_time > dtime)
306                                         q->vars.burst_time -= dtime;
307                                 else
308                                         q->vars.burst_time = 0;
309                         }
310                 }
311         }
312 }
313 
314 static void calculate_probability(struct Qdisc *sch)
315 {
316         struct pie_sched_data *q = qdisc_priv(sch);
317         u32 qlen = sch->qstats.backlog; /* queue size in bytes */
318         psched_time_t qdelay = 0;       /* in pschedtime */
319         psched_time_t qdelay_old = q->vars.qdelay;      /* in pschedtime */
320         s32 delta = 0;          /* determines the change in probability */
321         u32 oldprob;
322         u32 alpha, beta;
323         bool update_prob = true;
324 
325         q->vars.qdelay_old = q->vars.qdelay;
326 
327         if (q->vars.avg_dq_rate > 0)
328                 qdelay = (qlen << PIE_SCALE) / q->vars.avg_dq_rate;
329         else
330                 qdelay = 0;
331 
332         /* If qdelay is zero and qlen is not, it means qlen is very small, less
333          * than dequeue_rate, so we do not update probabilty in this round
334          */
335         if (qdelay == 0 && qlen != 0)
336                 update_prob = false;
337 
338         /* In the algorithm, alpha and beta are between 0 and 2 with typical
339          * value for alpha as 0.125. In this implementation, we use values 0-32
340          * passed from user space to represent this. Also, alpha and beta have
341          * unit of HZ and need to be scaled before they can used to update
342          * probability. alpha/beta are updated locally below by 1) scaling them
343          * appropriately 2) scaling down by 16 to come to 0-2 range.
344          * Please see paper for details.
345          *
346          * We scale alpha and beta differently depending on whether we are in
347          * light, medium or high dropping mode.
348          */
349         if (q->vars.prob < MAX_PROB / 100) {
350                 alpha =
351                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
352                 beta =
353                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 7;
354         } else if (q->vars.prob < MAX_PROB / 10) {
355                 alpha =
356                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
357                 beta =
358                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 5;
359         } else {
360                 alpha =
361                     (q->params.alpha * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
362                 beta =
363                     (q->params.beta * (MAX_PROB / PSCHED_TICKS_PER_SEC)) >> 4;
364         }
365 
366         /* alpha and beta should be between 0 and 32, in multiples of 1/16 */
367         delta += alpha * ((qdelay - q->params.target));
368         delta += beta * ((qdelay - qdelay_old));
369 
370         oldprob = q->vars.prob;
371 
372         /* to ensure we increase probability in steps of no more than 2% */
373         if (delta > (s32) (MAX_PROB / (100 / 2)) &&
374             q->vars.prob >= MAX_PROB / 10)
375                 delta = (MAX_PROB / 100) * 2;
376 
377         /* Non-linear drop:
378          * Tune drop probability to increase quickly for high delays(>= 250ms)
379          * 250ms is derived through experiments and provides error protection
380          */
381 
382         if (qdelay > (PSCHED_NS2TICKS(250 * NSEC_PER_MSEC)))
383                 delta += MAX_PROB / (100 / 2);
384 
385         q->vars.prob += delta;
386 
387         if (delta > 0) {
388                 /* prevent overflow */
389                 if (q->vars.prob < oldprob) {
390                         q->vars.prob = MAX_PROB;
391                         /* Prevent normalization error. If probability is at
392                          * maximum value already, we normalize it here, and
393                          * skip the check to do a non-linear drop in the next
394                          * section.
395                          */
396                         update_prob = false;
397                 }
398         } else {
399                 /* prevent underflow */
400                 if (q->vars.prob > oldprob)
401                         q->vars.prob = 0;
402         }
403 
404         /* Non-linear drop in probability: Reduce drop probability quickly if
405          * delay is 0 for 2 consecutive Tupdate periods.
406          */
407 
408         if ((qdelay == 0) && (qdelay_old == 0) && update_prob)
409                 q->vars.prob = (q->vars.prob * 98) / 100;
410 
411         q->vars.qdelay = qdelay;
412         q->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. We have atleast one estimate for the avg_dq_rate ie.,
418          *    is a non-zero value
419          */
420         if ((q->vars.qdelay < q->params.target / 2) &&
421             (q->vars.qdelay_old < q->params.target / 2) &&
422             (q->vars.prob == 0) &&
423             (q->vars.avg_dq_rate > 0))
424                 pie_vars_init(&q->vars);
425 }
426 
427 static void pie_timer(struct timer_list *t)
428 {
429         struct pie_sched_data *q = from_timer(q, t, adapt_timer);
430         struct Qdisc *sch = q->sch;
431         spinlock_t *root_lock = qdisc_lock(qdisc_root_sleeping(sch));
432 
433         spin_lock(root_lock);
434         calculate_probability(sch);
435 
436         /* reset the timer to fire after 'tupdate'. tupdate is in jiffies. */
437         if (q->params.tupdate)
438                 mod_timer(&q->adapt_timer, jiffies + q->params.tupdate);
439         spin_unlock(root_lock);
440 
441 }
442 
443 static int pie_init(struct Qdisc *sch, struct nlattr *opt,
444                     struct netlink_ext_ack *extack)
445 {
446         struct pie_sched_data *q = qdisc_priv(sch);
447 
448         pie_params_init(&q->params);
449         pie_vars_init(&q->vars);
450         sch->limit = q->params.limit;
451 
452         q->sch = sch;
453         timer_setup(&q->adapt_timer, pie_timer, 0);
454 
455         if (opt) {
456                 int err = pie_change(sch, opt, extack);
457 
458                 if (err)
459                         return err;
460         }
461 
462         mod_timer(&q->adapt_timer, jiffies + HZ / 2);
463         return 0;
464 }
465 
466 static int pie_dump(struct Qdisc *sch, struct sk_buff *skb)
467 {
468         struct pie_sched_data *q = qdisc_priv(sch);
469         struct nlattr *opts;
470 
471         opts = nla_nest_start(skb, TCA_OPTIONS);
472         if (opts == NULL)
473                 goto nla_put_failure;
474 
475         /* convert target from pschedtime to us */
476         if (nla_put_u32(skb, TCA_PIE_TARGET,
477                         ((u32) PSCHED_TICKS2NS(q->params.target)) /
478                         NSEC_PER_USEC) ||
479             nla_put_u32(skb, TCA_PIE_LIMIT, sch->limit) ||
480             nla_put_u32(skb, TCA_PIE_TUPDATE, jiffies_to_usecs(q->params.tupdate)) ||
481             nla_put_u32(skb, TCA_PIE_ALPHA, q->params.alpha) ||
482             nla_put_u32(skb, TCA_PIE_BETA, q->params.beta) ||
483             nla_put_u32(skb, TCA_PIE_ECN, q->params.ecn) ||
484             nla_put_u32(skb, TCA_PIE_BYTEMODE, q->params.bytemode))
485                 goto nla_put_failure;
486 
487         return nla_nest_end(skb, opts);
488 
489 nla_put_failure:
490         nla_nest_cancel(skb, opts);
491         return -1;
492 
493 }
494 
495 static int pie_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
496 {
497         struct pie_sched_data *q = qdisc_priv(sch);
498         struct tc_pie_xstats st = {
499                 .prob           = q->vars.prob,
500                 .delay          = ((u32) PSCHED_TICKS2NS(q->vars.qdelay)) /
501                                    NSEC_PER_USEC,
502                 /* unscale and return dq_rate in bytes per sec */
503                 .avg_dq_rate    = q->vars.avg_dq_rate *
504                                   (PSCHED_TICKS_PER_SEC) >> PIE_SCALE,
505                 .packets_in     = q->stats.packets_in,
506                 .overlimit      = q->stats.overlimit,
507                 .maxq           = q->stats.maxq,
508                 .dropped        = q->stats.dropped,
509                 .ecn_mark       = q->stats.ecn_mark,
510         };
511 
512         return gnet_stats_copy_app(d, &st, sizeof(st));
513 }
514 
515 static struct sk_buff *pie_qdisc_dequeue(struct Qdisc *sch)
516 {
517         struct sk_buff *skb;
518         skb = qdisc_dequeue_head(sch);
519 
520         if (!skb)
521                 return NULL;
522 
523         pie_process_dequeue(sch, skb);
524         return skb;
525 }
526 
527 static void pie_reset(struct Qdisc *sch)
528 {
529         struct pie_sched_data *q = qdisc_priv(sch);
530         qdisc_reset_queue(sch);
531         pie_vars_init(&q->vars);
532 }
533 
534 static void pie_destroy(struct Qdisc *sch)
535 {
536         struct pie_sched_data *q = qdisc_priv(sch);
537         q->params.tupdate = 0;
538         del_timer_sync(&q->adapt_timer);
539 }
540 
541 static struct Qdisc_ops pie_qdisc_ops __read_mostly = {
542         .id = "pie",
543         .priv_size      = sizeof(struct pie_sched_data),
544         .enqueue        = pie_qdisc_enqueue,
545         .dequeue        = pie_qdisc_dequeue,
546         .peek           = qdisc_peek_dequeued,
547         .init           = pie_init,
548         .destroy        = pie_destroy,
549         .reset          = pie_reset,
550         .change         = pie_change,
551         .dump           = pie_dump,
552         .dump_stats     = pie_dump_stats,
553         .owner          = THIS_MODULE,
554 };
555 
556 static int __init pie_module_init(void)
557 {
558         return register_qdisc(&pie_qdisc_ops);
559 }
560 
561 static void __exit pie_module_exit(void)
562 {
563         unregister_qdisc(&pie_qdisc_ops);
564 }
565 
566 module_init(pie_module_init);
567 module_exit(pie_module_exit);
568 
569 MODULE_DESCRIPTION("Proportional Integral controller Enhanced (PIE) scheduler");
570 MODULE_AUTHOR("Vijay Subramanian");
571 MODULE_AUTHOR("Mythili Prabhu");
572 MODULE_LICENSE("GPL");
573 

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