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 {
120 struct choke_sched_data *q = qdisc_priv(sch);
121 struct sk_buff *skb = q->tab[idx];
122
123 q->tab[idx] = NULL;
124
125 if (idx == q->head)
126 choke_zap_head_holes(q);
127 if (idx == q->tail)
128 choke_zap_tail_holes(q);
129
130 qdisc_qstats_backlog_dec(sch, skb);
131 qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
132 qdisc_drop(skb, sch);
133 --sch->q.qlen;
134 }
135
136 struct choke_skb_cb {
137 u16 classid;
138 u8 keys_valid;
139 struct flow_keys_digest keys;
140 };
141
142 static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
143 {
144 qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
145 return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
146 }
147
148 static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
149 {
150 choke_skb_cb(skb)->classid = classid;
151 }
152
153 static u16 choke_get_classid(const struct sk_buff *skb)
154 {
155 return choke_skb_cb(skb)->classid;
156 }
157
158 /*
159 * Compare flow of two packets
160 * Returns true only if source and destination address and port match.
161 * false for special cases
162 */
163 static bool choke_match_flow(struct sk_buff *skb1,
164 struct sk_buff *skb2)
165 {
166 struct flow_keys temp;
167
168 if (skb1->protocol != skb2->protocol)
169 return false;
170
171 if (!choke_skb_cb(skb1)->keys_valid) {
172 choke_skb_cb(skb1)->keys_valid = 1;
173 skb_flow_dissect_flow_keys(skb1, &temp, 0);
174 make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
175 }
176
177 if (!choke_skb_cb(skb2)->keys_valid) {
178 choke_skb_cb(skb2)->keys_valid = 1;
179 skb_flow_dissect_flow_keys(skb2, &temp, 0);
180 make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
181 }
182
183 return !memcmp(&choke_skb_cb(skb1)->keys,
184 &choke_skb_cb(skb2)->keys,
185 sizeof(choke_skb_cb(skb1)->keys));
186 }
187
188 /*
189 * Classify flow using either:
190 * 1. pre-existing classification result in skb
191 * 2. fast internal classification
192 * 3. use TC filter based classification
193 */
194 static bool choke_classify(struct sk_buff *skb,
195 struct Qdisc *sch, int *qerr)
196
197 {
198 struct choke_sched_data *q = qdisc_priv(sch);
199 struct tcf_result res;
200 struct tcf_proto *fl;
201 int result;
202
203 fl = rcu_dereference_bh(q->filter_list);
204 result = tc_classify(skb, fl, &res, false);
205 if (result >= 0) {
206 #ifdef CONFIG_NET_CLS_ACT
207 switch (result) {
208 case TC_ACT_STOLEN:
209 case TC_ACT_QUEUED:
210 *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
211 case TC_ACT_SHOT:
212 return false;
213 }
214 #endif
215 choke_set_classid(skb, TC_H_MIN(res.classid));
216 return true;
217 }
218
219 return false;
220 }
221
222 /*
223 * Select a packet at random from queue
224 * HACK: since queue can have holes from previous deletion; retry several
225 * times to find a random skb but then just give up and return the head
226 * Will return NULL if queue is empty (q->head == q->tail)
227 */
228 static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
229 unsigned int *pidx)
230 {
231 struct sk_buff *skb;
232 int retrys = 3;
233
234 do {
235 *pidx = (q->head + prandom_u32_max(choke_len(q))) & q->tab_mask;
236 skb = q->tab[*pidx];
237 if (skb)
238 return skb;
239 } while (--retrys > 0);
240
241 return q->tab[*pidx = q->head];
242 }
243
244 /*
245 * Compare new packet with random packet in queue
246 * returns true if matched and sets *pidx
247 */
248 static bool choke_match_random(const struct choke_sched_data *q,
249 struct sk_buff *nskb,
250 unsigned int *pidx)
251 {
252 struct sk_buff *oskb;
253
254 if (q->head == q->tail)
255 return false;
256
257 oskb = choke_peek_random(q, pidx);
258 if (rcu_access_pointer(q->filter_list))
259 return choke_get_classid(nskb) == choke_get_classid(oskb);
260
261 return choke_match_flow(oskb, nskb);
262 }
263
264 static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
265 {
266 int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
267 struct choke_sched_data *q = qdisc_priv(sch);
268 const struct red_parms *p = &q->parms;
269
270 if (rcu_access_pointer(q->filter_list)) {
271 /* If using external classifiers, get result and record it. */
272 if (!choke_classify(skb, sch, &ret))
273 goto other_drop; /* Packet was eaten by filter */
274 }
275
276 choke_skb_cb(skb)->keys_valid = 0;
277 /* Compute average queue usage (see RED) */
278 q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
279 if (red_is_idling(&q->vars))
280 red_end_of_idle_period(&q->vars);
281
282 /* Is queue small? */
283 if (q->vars.qavg <= p->qth_min)
284 q->vars.qcount = -1;
285 else {
286 unsigned int idx;
287
288 /* Draw a packet at random from queue and compare flow */
289 if (choke_match_random(q, skb, &idx)) {
290 q->stats.matched++;
291 choke_drop_by_idx(sch, idx);
292 goto congestion_drop;
293 }
294
295 /* Queue is large, always mark/drop */
296 if (q->vars.qavg > p->qth_max) {
297 q->vars.qcount = -1;
298
299 qdisc_qstats_overlimit(sch);
300 if (use_harddrop(q) || !use_ecn(q) ||
301 !INET_ECN_set_ce(skb)) {
302 q->stats.forced_drop++;
303 goto congestion_drop;
304 }
305
306 q->stats.forced_mark++;
307 } else if (++q->vars.qcount) {
308 if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
309 q->vars.qcount = 0;
310 q->vars.qR = red_random(p);
311
312 qdisc_qstats_overlimit(sch);
313 if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
314 q->stats.prob_drop++;
315 goto congestion_drop;
316 }
317
318 q->stats.prob_mark++;
319 }
320 } else
321 q->vars.qR = red_random(p);
322 }
323
324 /* Admit new packet */
325 if (sch->q.qlen < q->limit) {
326 q->tab[q->tail] = skb;
327 q->tail = (q->tail + 1) & q->tab_mask;
328 ++sch->q.qlen;
329 qdisc_qstats_backlog_inc(sch, skb);
330 return NET_XMIT_SUCCESS;
331 }
332
333 q->stats.pdrop++;
334 return qdisc_drop(skb, sch);
335
336 congestion_drop:
337 qdisc_drop(skb, sch);
338 return NET_XMIT_CN;
339
340 other_drop:
341 if (ret & __NET_XMIT_BYPASS)
342 qdisc_qstats_drop(sch);
343 kfree_skb(skb);
344 return ret;
345 }
346
347 static struct sk_buff *choke_dequeue(struct Qdisc *sch)
348 {
349 struct choke_sched_data *q = qdisc_priv(sch);
350 struct sk_buff *skb;
351
352 if (q->head == q->tail) {
353 if (!red_is_idling(&q->vars))
354 red_start_of_idle_period(&q->vars);
355 return NULL;
356 }
357
358 skb = q->tab[q->head];
359 q->tab[q->head] = NULL;
360 choke_zap_head_holes(q);
361 --sch->q.qlen;
362 qdisc_qstats_backlog_dec(sch, skb);
363 qdisc_bstats_update(sch, skb);
364
365 return skb;
366 }
367
368 static unsigned int choke_drop(struct Qdisc *sch)
369 {
370 struct choke_sched_data *q = qdisc_priv(sch);
371 unsigned int len;
372
373 len = qdisc_queue_drop(sch);
374 if (len > 0)
375 q->stats.other++;
376 else {
377 if (!red_is_idling(&q->vars))
378 red_start_of_idle_period(&q->vars);
379 }
380
381 return len;
382 }
383
384 static void choke_reset(struct Qdisc *sch)
385 {
386 struct choke_sched_data *q = qdisc_priv(sch);
387
388 while (q->head != q->tail) {
389 struct sk_buff *skb = q->tab[q->head];
390
391 q->head = (q->head + 1) & q->tab_mask;
392 if (!skb)
393 continue;
394 qdisc_qstats_backlog_dec(sch, skb);
395 --sch->q.qlen;
396 qdisc_drop(skb, sch);
397 }
398
399 if (q->tab)
400 memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
401 q->head = q->tail = 0;
402 red_restart(&q->vars);
403 }
404
405 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
406 [TCA_CHOKE_PARMS] = { .len = sizeof(struct tc_red_qopt) },
407 [TCA_CHOKE_STAB] = { .len = RED_STAB_SIZE },
408 [TCA_CHOKE_MAX_P] = { .type = NLA_U32 },
409 };
410
411
412 static void choke_free(void *addr)
413 {
414 kvfree(addr);
415 }
416
417 static int choke_change(struct Qdisc *sch, struct nlattr *opt)
418 {
419 struct choke_sched_data *q = qdisc_priv(sch);
420 struct nlattr *tb[TCA_CHOKE_MAX + 1];
421 const struct tc_red_qopt *ctl;
422 int err;
423 struct sk_buff **old = NULL;
424 unsigned int mask;
425 u32 max_P;
426 u8 *stab;
427
428 if (opt == NULL)
429 return -EINVAL;
430
431 err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
432 if (err < 0)
433 return err;
434
435 if (tb[TCA_CHOKE_PARMS] == NULL ||
436 tb[TCA_CHOKE_STAB] == NULL)
437 return -EINVAL;
438
439 max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
440
441 ctl = nla_data(tb[TCA_CHOKE_PARMS]);
442 stab = nla_data(tb[TCA_CHOKE_STAB]);
443 if (!red_check_params(ctl->qth_min, ctl->qth_max, ctl->Wlog, ctl->Scell_log, stab))
444 return -EINVAL;
445
446 if (ctl->limit > CHOKE_MAX_QUEUE)
447 return -EINVAL;
448
449 mask = roundup_pow_of_two(ctl->limit + 1) - 1;
450 if (mask != q->tab_mask) {
451 struct sk_buff **ntab;
452
453 ntab = kcalloc(mask + 1, sizeof(struct sk_buff *),
454 GFP_KERNEL | __GFP_NOWARN);
455 if (!ntab)
456 ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
457 if (!ntab)
458 return -ENOMEM;
459
460 sch_tree_lock(sch);
461 old = q->tab;
462 if (old) {
463 unsigned int oqlen = sch->q.qlen, tail = 0;
464 unsigned dropped = 0;
465
466 while (q->head != q->tail) {
467 struct sk_buff *skb = q->tab[q->head];
468
469 q->head = (q->head + 1) & q->tab_mask;
470 if (!skb)
471 continue;
472 if (tail < mask) {
473 ntab[tail++] = skb;
474 continue;
475 }
476 dropped += qdisc_pkt_len(skb);
477 qdisc_qstats_backlog_dec(sch, skb);
478 --sch->q.qlen;
479 qdisc_drop(skb, sch);
480 }
481 qdisc_tree_reduce_backlog(sch, oqlen - sch->q.qlen, dropped);
482 q->head = 0;
483 q->tail = tail;
484 }
485
486 q->tab_mask = mask;
487 q->tab = ntab;
488 } else
489 sch_tree_lock(sch);
490
491 q->flags = ctl->flags;
492 q->limit = ctl->limit;
493
494 red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
495 ctl->Plog, ctl->Scell_log,
496 stab,
497 max_P);
498 red_set_vars(&q->vars);
499
500 if (q->head == q->tail)
501 red_end_of_idle_period(&q->vars);
502
503 sch_tree_unlock(sch);
504 choke_free(old);
505 return 0;
506 }
507
508 static int choke_init(struct Qdisc *sch, struct nlattr *opt)
509 {
510 return choke_change(sch, opt);
511 }
512
513 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
514 {
515 struct choke_sched_data *q = qdisc_priv(sch);
516 struct nlattr *opts = NULL;
517 struct tc_red_qopt opt = {
518 .limit = q->limit,
519 .flags = q->flags,
520 .qth_min = q->parms.qth_min >> q->parms.Wlog,
521 .qth_max = q->parms.qth_max >> q->parms.Wlog,
522 .Wlog = q->parms.Wlog,
523 .Plog = q->parms.Plog,
524 .Scell_log = q->parms.Scell_log,
525 };
526
527 opts = nla_nest_start(skb, TCA_OPTIONS);
528 if (opts == NULL)
529 goto nla_put_failure;
530
531 if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
532 nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
533 goto nla_put_failure;
534 return nla_nest_end(skb, opts);
535
536 nla_put_failure:
537 nla_nest_cancel(skb, opts);
538 return -EMSGSIZE;
539 }
540
541 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
542 {
543 struct choke_sched_data *q = qdisc_priv(sch);
544 struct tc_choke_xstats st = {
545 .early = q->stats.prob_drop + q->stats.forced_drop,
546 .marked = q->stats.prob_mark + q->stats.forced_mark,
547 .pdrop = q->stats.pdrop,
548 .other = q->stats.other,
549 .matched = q->stats.matched,
550 };
551
552 return gnet_stats_copy_app(d, &st, sizeof(st));
553 }
554
555 static void choke_destroy(struct Qdisc *sch)
556 {
557 struct choke_sched_data *q = qdisc_priv(sch);
558
559 tcf_destroy_chain(&q->filter_list);
560 choke_free(q->tab);
561 }
562
563 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
564 {
565 struct choke_sched_data *q = qdisc_priv(sch);
566
567 return (q->head != q->tail) ? q->tab[q->head] : NULL;
568 }
569
570 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
571 .id = "choke",
572 .priv_size = sizeof(struct choke_sched_data),
573
574 .enqueue = choke_enqueue,
575 .dequeue = choke_dequeue,
576 .peek = choke_peek_head,
577 .drop = choke_drop,
578 .init = choke_init,
579 .destroy = choke_destroy,
580 .reset = choke_reset,
581 .change = choke_change,
582 .dump = choke_dump,
583 .dump_stats = choke_dump_stats,
584 .owner = THIS_MODULE,
585 };
586
587 static int __init choke_module_init(void)
588 {
589 return register_qdisc(&choke_qdisc_ops);
590 }
591
592 static void __exit choke_module_exit(void)
593 {
594 unregister_qdisc(&choke_qdisc_ops);
595 }
596
597 module_init(choke_module_init)
598 module_exit(choke_module_exit)
599
600 MODULE_LICENSE("GPL");
601
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