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Linux/net/sched/sch_choke.c

  1 /*
  2  * net/sched/sch_choke.c        CHOKE scheduler
  3  *
  4  * Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
  5  * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
  6  *
  7  * This program is free software; you can redistribute it and/or
  8  * modify it under the terms of the GNU General Public License
  9  * version 2 as published by the Free Software Foundation.
 10  *
 11  */
 12 
 13 #include <linux/module.h>
 14 #include <linux/types.h>
 15 #include <linux/kernel.h>
 16 #include <linux/skbuff.h>
 17 #include <linux/vmalloc.h>
 18 #include <net/pkt_sched.h>
 19 #include <net/inet_ecn.h>
 20 #include <net/red.h>
 21 #include <net/flow_dissector.h>
 22 
 23 /*
 24    CHOKe stateless AQM for fair bandwidth allocation
 25    =================================================
 26 
 27    CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
 28    unresponsive flows) is a variant of RED that penalizes misbehaving flows but
 29    maintains no flow state. The difference from RED is an additional step
 30    during the enqueuing process. If average queue size is over the
 31    low threshold (qmin), a packet is chosen at random from the queue.
 32    If both the new and chosen packet are from the same flow, both
 33    are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
 34    needs to access packets in queue randomly. It has a minimal class
 35    interface to allow overriding the builtin flow classifier with
 36    filters.
 37 
 38    Source:
 39    R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
 40    Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
 41    IEEE INFOCOM, 2000.
 42 
 43    A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
 44    Characteristics", IEEE/ACM Transactions on Networking, 2004
 45 
 46  */
 47 
 48 /* Upper bound on size of sk_buff table (packets) */
 49 #define CHOKE_MAX_QUEUE (128*1024 - 1)
 50 
 51 struct choke_sched_data {
 52 /* Parameters */
 53         u32              limit;
 54         unsigned char    flags;
 55 
 56         struct red_parms parms;
 57 
 58 /* Variables */
 59         struct red_vars  vars;
 60         struct tcf_proto __rcu *filter_list;
 61         struct {
 62                 u32     prob_drop;      /* Early probability drops */
 63                 u32     prob_mark;      /* Early probability marks */
 64                 u32     forced_drop;    /* Forced drops, qavg > max_thresh */
 65                 u32     forced_mark;    /* Forced marks, qavg > max_thresh */
 66                 u32     pdrop;          /* Drops due to queue limits */
 67                 u32     other;          /* Drops due to drop() calls */
 68                 u32     matched;        /* Drops to flow match */
 69         } stats;
 70 
 71         unsigned int     head;
 72         unsigned int     tail;
 73 
 74         unsigned int     tab_mask; /* size - 1 */
 75 
 76         struct sk_buff **tab;
 77 };
 78 
 79 /* number of elements in queue including holes */
 80 static unsigned int choke_len(const struct choke_sched_data *q)
 81 {
 82         return (q->tail - q->head) & q->tab_mask;
 83 }
 84 
 85 /* Is ECN parameter configured */
 86 static int use_ecn(const struct choke_sched_data *q)
 87 {
 88         return q->flags & TC_RED_ECN;
 89 }
 90 
 91 /* Should packets over max just be dropped (versus marked) */
 92 static int use_harddrop(const struct choke_sched_data *q)
 93 {
 94         return q->flags & TC_RED_HARDDROP;
 95 }
 96 
 97 /* Move head pointer forward to skip over holes */
 98 static void choke_zap_head_holes(struct choke_sched_data *q)
 99 {
100         do {
101                 q->head = (q->head + 1) & q->tab_mask;
102                 if (q->head == q->tail)
103                         break;
104         } while (q->tab[q->head] == NULL);
105 }
106 
107 /* Move tail pointer backwards to reuse holes */
108 static void choke_zap_tail_holes(struct choke_sched_data *q)
109 {
110         do {
111                 q->tail = (q->tail - 1) & q->tab_mask;
112                 if (q->head == q->tail)
113                         break;
114         } while (q->tab[q->tail] == NULL);
115 }
116 
117 /* Drop packet from queue array by creating a "hole" */
118 static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
119                               struct sk_buff **to_free)
120 {
121         struct choke_sched_data *q = qdisc_priv(sch);
122         struct sk_buff *skb = q->tab[idx];
123 
124         q->tab[idx] = NULL;
125 
126         if (idx == q->head)
127                 choke_zap_head_holes(q);
128         if (idx == q->tail)
129                 choke_zap_tail_holes(q);
130 
131         qdisc_qstats_backlog_dec(sch, skb);
132         qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
133         qdisc_drop(skb, sch, to_free);
134         --sch->q.qlen;
135 }
136 
137 struct choke_skb_cb {
138         u16                     classid;
139         u8                      keys_valid;
140         struct                  flow_keys_digest keys;
141 };
142 
143 static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
144 {
145         qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
146         return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
147 }
148 
149 static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
150 {
151         choke_skb_cb(skb)->classid = classid;
152 }
153 
154 static u16 choke_get_classid(const struct sk_buff *skb)
155 {
156         return choke_skb_cb(skb)->classid;
157 }
158 
159 /*
160  * Compare flow of two packets
161  *  Returns true only if source and destination address and port match.
162  *          false for special cases
163  */
164 static bool choke_match_flow(struct sk_buff *skb1,
165                              struct sk_buff *skb2)
166 {
167         struct flow_keys temp;
168 
169         if (skb1->protocol != skb2->protocol)
170                 return false;
171 
172         if (!choke_skb_cb(skb1)->keys_valid) {
173                 choke_skb_cb(skb1)->keys_valid = 1;
174                 skb_flow_dissect_flow_keys(skb1, &temp, 0);
175                 make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
176         }
177 
178         if (!choke_skb_cb(skb2)->keys_valid) {
179                 choke_skb_cb(skb2)->keys_valid = 1;
180                 skb_flow_dissect_flow_keys(skb2, &temp, 0);
181                 make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
182         }
183 
184         return !memcmp(&choke_skb_cb(skb1)->keys,
185                        &choke_skb_cb(skb2)->keys,
186                        sizeof(choke_skb_cb(skb1)->keys));
187 }
188 
189 /*
190  * Classify flow using either:
191  *  1. pre-existing classification result in skb
192  *  2. fast internal classification
193  *  3. use TC filter based classification
194  */
195 static bool choke_classify(struct sk_buff *skb,
196                            struct Qdisc *sch, int *qerr)
197 
198 {
199         struct choke_sched_data *q = qdisc_priv(sch);
200         struct tcf_result res;
201         struct tcf_proto *fl;
202         int result;
203 
204         fl = rcu_dereference_bh(q->filter_list);
205         result = tc_classify(skb, fl, &res, false);
206         if (result >= 0) {
207 #ifdef CONFIG_NET_CLS_ACT
208                 switch (result) {
209                 case TC_ACT_STOLEN:
210                 case TC_ACT_QUEUED:
211                         *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
212                 case TC_ACT_SHOT:
213                         return false;
214                 }
215 #endif
216                 choke_set_classid(skb, TC_H_MIN(res.classid));
217                 return true;
218         }
219 
220         return false;
221 }
222 
223 /*
224  * Select a packet at random from queue
225  * HACK: since queue can have holes from previous deletion; retry several
226  *   times to find a random skb but then just give up and return the head
227  * Will return NULL if queue is empty (q->head == q->tail)
228  */
229 static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
230                                          unsigned int *pidx)
231 {
232         struct sk_buff *skb;
233         int retrys = 3;
234 
235         do {
236                 *pidx = (q->head + prandom_u32_max(choke_len(q))) & q->tab_mask;
237                 skb = q->tab[*pidx];
238                 if (skb)
239                         return skb;
240         } while (--retrys > 0);
241 
242         return q->tab[*pidx = q->head];
243 }
244 
245 /*
246  * Compare new packet with random packet in queue
247  * returns true if matched and sets *pidx
248  */
249 static bool choke_match_random(const struct choke_sched_data *q,
250                                struct sk_buff *nskb,
251                                unsigned int *pidx)
252 {
253         struct sk_buff *oskb;
254 
255         if (q->head == q->tail)
256                 return false;
257 
258         oskb = choke_peek_random(q, pidx);
259         if (rcu_access_pointer(q->filter_list))
260                 return choke_get_classid(nskb) == choke_get_classid(oskb);
261 
262         return choke_match_flow(oskb, nskb);
263 }
264 
265 static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
266                          struct sk_buff **to_free)
267 {
268         int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
269         struct choke_sched_data *q = qdisc_priv(sch);
270         const struct red_parms *p = &q->parms;
271 
272         if (rcu_access_pointer(q->filter_list)) {
273                 /* If using external classifiers, get result and record it. */
274                 if (!choke_classify(skb, sch, &ret))
275                         goto other_drop;        /* Packet was eaten by filter */
276         }
277 
278         choke_skb_cb(skb)->keys_valid = 0;
279         /* Compute average queue usage (see RED) */
280         q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
281         if (red_is_idling(&q->vars))
282                 red_end_of_idle_period(&q->vars);
283 
284         /* Is queue small? */
285         if (q->vars.qavg <= p->qth_min)
286                 q->vars.qcount = -1;
287         else {
288                 unsigned int idx;
289 
290                 /* Draw a packet at random from queue and compare flow */
291                 if (choke_match_random(q, skb, &idx)) {
292                         q->stats.matched++;
293                         choke_drop_by_idx(sch, idx, to_free);
294                         goto congestion_drop;
295                 }
296 
297                 /* Queue is large, always mark/drop */
298                 if (q->vars.qavg > p->qth_max) {
299                         q->vars.qcount = -1;
300 
301                         qdisc_qstats_overlimit(sch);
302                         if (use_harddrop(q) || !use_ecn(q) ||
303                             !INET_ECN_set_ce(skb)) {
304                                 q->stats.forced_drop++;
305                                 goto congestion_drop;
306                         }
307 
308                         q->stats.forced_mark++;
309                 } else if (++q->vars.qcount) {
310                         if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
311                                 q->vars.qcount = 0;
312                                 q->vars.qR = red_random(p);
313 
314                                 qdisc_qstats_overlimit(sch);
315                                 if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
316                                         q->stats.prob_drop++;
317                                         goto congestion_drop;
318                                 }
319 
320                                 q->stats.prob_mark++;
321                         }
322                 } else
323                         q->vars.qR = red_random(p);
324         }
325 
326         /* Admit new packet */
327         if (sch->q.qlen < q->limit) {
328                 q->tab[q->tail] = skb;
329                 q->tail = (q->tail + 1) & q->tab_mask;
330                 ++sch->q.qlen;
331                 qdisc_qstats_backlog_inc(sch, skb);
332                 return NET_XMIT_SUCCESS;
333         }
334 
335         q->stats.pdrop++;
336         return qdisc_drop(skb, sch, to_free);
337 
338 congestion_drop:
339         qdisc_drop(skb, sch, to_free);
340         return NET_XMIT_CN;
341 
342 other_drop:
343         if (ret & __NET_XMIT_BYPASS)
344                 qdisc_qstats_drop(sch);
345         __qdisc_drop(skb, to_free);
346         return ret;
347 }
348 
349 static struct sk_buff *choke_dequeue(struct Qdisc *sch)
350 {
351         struct choke_sched_data *q = qdisc_priv(sch);
352         struct sk_buff *skb;
353 
354         if (q->head == q->tail) {
355                 if (!red_is_idling(&q->vars))
356                         red_start_of_idle_period(&q->vars);
357                 return NULL;
358         }
359 
360         skb = q->tab[q->head];
361         q->tab[q->head] = NULL;
362         choke_zap_head_holes(q);
363         --sch->q.qlen;
364         qdisc_qstats_backlog_dec(sch, skb);
365         qdisc_bstats_update(sch, skb);
366 
367         return skb;
368 }
369 
370 static void choke_reset(struct Qdisc *sch)
371 {
372         struct choke_sched_data *q = qdisc_priv(sch);
373 
374         while (q->head != q->tail) {
375                 struct sk_buff *skb = q->tab[q->head];
376 
377                 q->head = (q->head + 1) & q->tab_mask;
378                 if (!skb)
379                         continue;
380                 rtnl_qdisc_drop(skb, sch);
381         }
382 
383         sch->q.qlen = 0;
384         sch->qstats.backlog = 0;
385         memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
386         q->head = q->tail = 0;
387         red_restart(&q->vars);
388 }
389 
390 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
391         [TCA_CHOKE_PARMS]       = { .len = sizeof(struct tc_red_qopt) },
392         [TCA_CHOKE_STAB]        = { .len = RED_STAB_SIZE },
393         [TCA_CHOKE_MAX_P]       = { .type = NLA_U32 },
394 };
395 
396 
397 static void choke_free(void *addr)
398 {
399         kvfree(addr);
400 }
401 
402 static int choke_change(struct Qdisc *sch, struct nlattr *opt)
403 {
404         struct choke_sched_data *q = qdisc_priv(sch);
405         struct nlattr *tb[TCA_CHOKE_MAX + 1];
406         const struct tc_red_qopt *ctl;
407         int err;
408         struct sk_buff **old = NULL;
409         unsigned int mask;
410         u32 max_P;
411 
412         if (opt == NULL)
413                 return -EINVAL;
414 
415         err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
416         if (err < 0)
417                 return err;
418 
419         if (tb[TCA_CHOKE_PARMS] == NULL ||
420             tb[TCA_CHOKE_STAB] == NULL)
421                 return -EINVAL;
422 
423         max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
424 
425         ctl = nla_data(tb[TCA_CHOKE_PARMS]);
426 
427         if (ctl->limit > CHOKE_MAX_QUEUE)
428                 return -EINVAL;
429 
430         mask = roundup_pow_of_two(ctl->limit + 1) - 1;
431         if (mask != q->tab_mask) {
432                 struct sk_buff **ntab;
433 
434                 ntab = kcalloc(mask + 1, sizeof(struct sk_buff *),
435                                GFP_KERNEL | __GFP_NOWARN);
436                 if (!ntab)
437                         ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
438                 if (!ntab)
439                         return -ENOMEM;
440 
441                 sch_tree_lock(sch);
442                 old = q->tab;
443                 if (old) {
444                         unsigned int oqlen = sch->q.qlen, tail = 0;
445                         unsigned dropped = 0;
446 
447                         while (q->head != q->tail) {
448                                 struct sk_buff *skb = q->tab[q->head];
449 
450                                 q->head = (q->head + 1) & q->tab_mask;
451                                 if (!skb)
452                                         continue;
453                                 if (tail < mask) {
454                                         ntab[tail++] = skb;
455                                         continue;
456                                 }
457                                 dropped += qdisc_pkt_len(skb);
458                                 qdisc_qstats_backlog_dec(sch, skb);
459                                 --sch->q.qlen;
460                                 rtnl_qdisc_drop(skb, sch);
461                         }
462                         qdisc_tree_reduce_backlog(sch, oqlen - sch->q.qlen, dropped);
463                         q->head = 0;
464                         q->tail = tail;
465                 }
466 
467                 q->tab_mask = mask;
468                 q->tab = ntab;
469         } else
470                 sch_tree_lock(sch);
471 
472         q->flags = ctl->flags;
473         q->limit = ctl->limit;
474 
475         red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
476                       ctl->Plog, ctl->Scell_log,
477                       nla_data(tb[TCA_CHOKE_STAB]),
478                       max_P);
479         red_set_vars(&q->vars);
480 
481         if (q->head == q->tail)
482                 red_end_of_idle_period(&q->vars);
483 
484         sch_tree_unlock(sch);
485         choke_free(old);
486         return 0;
487 }
488 
489 static int choke_init(struct Qdisc *sch, struct nlattr *opt)
490 {
491         return choke_change(sch, opt);
492 }
493 
494 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
495 {
496         struct choke_sched_data *q = qdisc_priv(sch);
497         struct nlattr *opts = NULL;
498         struct tc_red_qopt opt = {
499                 .limit          = q->limit,
500                 .flags          = q->flags,
501                 .qth_min        = q->parms.qth_min >> q->parms.Wlog,
502                 .qth_max        = q->parms.qth_max >> q->parms.Wlog,
503                 .Wlog           = q->parms.Wlog,
504                 .Plog           = q->parms.Plog,
505                 .Scell_log      = q->parms.Scell_log,
506         };
507 
508         opts = nla_nest_start(skb, TCA_OPTIONS);
509         if (opts == NULL)
510                 goto nla_put_failure;
511 
512         if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
513             nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
514                 goto nla_put_failure;
515         return nla_nest_end(skb, opts);
516 
517 nla_put_failure:
518         nla_nest_cancel(skb, opts);
519         return -EMSGSIZE;
520 }
521 
522 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
523 {
524         struct choke_sched_data *q = qdisc_priv(sch);
525         struct tc_choke_xstats st = {
526                 .early  = q->stats.prob_drop + q->stats.forced_drop,
527                 .marked = q->stats.prob_mark + q->stats.forced_mark,
528                 .pdrop  = q->stats.pdrop,
529                 .other  = q->stats.other,
530                 .matched = q->stats.matched,
531         };
532 
533         return gnet_stats_copy_app(d, &st, sizeof(st));
534 }
535 
536 static void choke_destroy(struct Qdisc *sch)
537 {
538         struct choke_sched_data *q = qdisc_priv(sch);
539 
540         tcf_destroy_chain(&q->filter_list);
541         choke_free(q->tab);
542 }
543 
544 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
545 {
546         struct choke_sched_data *q = qdisc_priv(sch);
547 
548         return (q->head != q->tail) ? q->tab[q->head] : NULL;
549 }
550 
551 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
552         .id             =       "choke",
553         .priv_size      =       sizeof(struct choke_sched_data),
554 
555         .enqueue        =       choke_enqueue,
556         .dequeue        =       choke_dequeue,
557         .peek           =       choke_peek_head,
558         .init           =       choke_init,
559         .destroy        =       choke_destroy,
560         .reset          =       choke_reset,
561         .change         =       choke_change,
562         .dump           =       choke_dump,
563         .dump_stats     =       choke_dump_stats,
564         .owner          =       THIS_MODULE,
565 };
566 
567 static int __init choke_module_init(void)
568 {
569         return register_qdisc(&choke_qdisc_ops);
570 }
571 
572 static void __exit choke_module_exit(void)
573 {
574         unregister_qdisc(&choke_qdisc_ops);
575 }
576 
577 module_init(choke_module_init)
578 module_exit(choke_module_exit)
579 
580 MODULE_LICENSE("GPL");
581 

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