1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * net/sched/sch_choke.c CHOKE scheduler
4 *
5 * Copyright (c) 2011 Stephen Hemminger <shemminger@vyatta.com>
6 * Copyright (c) 2011 Eric Dumazet <eric.dumazet@gmail.com>
7 */
8
9 #include <linux/module.h>
10 #include <linux/types.h>
11 #include <linux/kernel.h>
12 #include <linux/skbuff.h>
13 #include <linux/vmalloc.h>
14 #include <net/pkt_sched.h>
15 #include <net/pkt_cls.h>
16 #include <net/inet_ecn.h>
17 #include <net/red.h>
18 #include <net/flow_dissector.h>
19
20 /*
21 CHOKe stateless AQM for fair bandwidth allocation
22 =================================================
23
24 CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
25 unresponsive flows) is a variant of RED that penalizes misbehaving flows but
26 maintains no flow state. The difference from RED is an additional step
27 during the enqueuing process. If average queue size is over the
28 low threshold (qmin), a packet is chosen at random from the queue.
29 If both the new and chosen packet are from the same flow, both
30 are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
31 needs to access packets in queue randomly. It has a minimal class
32 interface to allow overriding the builtin flow classifier with
33 filters.
34
35 Source:
36 R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
37 Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
38 IEEE INFOCOM, 2000.
39
40 A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
41 Characteristics", IEEE/ACM Transactions on Networking, 2004
42
43 */
44
45 /* Upper bound on size of sk_buff table (packets) */
46 #define CHOKE_MAX_QUEUE (128*1024 - 1)
47
48 struct choke_sched_data {
49 /* Parameters */
50 u32 limit;
51 unsigned char flags;
52
53 struct red_parms parms;
54
55 /* Variables */
56 struct red_vars vars;
57 struct {
58 u32 prob_drop; /* Early probability drops */
59 u32 prob_mark; /* Early probability marks */
60 u32 forced_drop; /* Forced drops, qavg > max_thresh */
61 u32 forced_mark; /* Forced marks, qavg > max_thresh */
62 u32 pdrop; /* Drops due to queue limits */
63 u32 other; /* Drops due to drop() calls */
64 u32 matched; /* Drops to flow match */
65 } stats;
66
67 unsigned int head;
68 unsigned int tail;
69
70 unsigned int tab_mask; /* size - 1 */
71
72 struct sk_buff **tab;
73 };
74
75 /* number of elements in queue including holes */
choke_len(const struct choke_sched_data * q)76 static unsigned int choke_len(const struct choke_sched_data *q)
77 {
78 return (q->tail - q->head) & q->tab_mask;
79 }
80
81 /* Is ECN parameter configured */
use_ecn(const struct choke_sched_data * q)82 static int use_ecn(const struct choke_sched_data *q)
83 {
84 return q->flags & TC_RED_ECN;
85 }
86
87 /* Should packets over max just be dropped (versus marked) */
use_harddrop(const struct choke_sched_data * q)88 static int use_harddrop(const struct choke_sched_data *q)
89 {
90 return q->flags & TC_RED_HARDDROP;
91 }
92
93 /* Move head pointer forward to skip over holes */
choke_zap_head_holes(struct choke_sched_data * q)94 static void choke_zap_head_holes(struct choke_sched_data *q)
95 {
96 do {
97 q->head = (q->head + 1) & q->tab_mask;
98 if (q->head == q->tail)
99 break;
100 } while (q->tab[q->head] == NULL);
101 }
102
103 /* Move tail pointer backwards to reuse holes */
choke_zap_tail_holes(struct choke_sched_data * q)104 static void choke_zap_tail_holes(struct choke_sched_data *q)
105 {
106 do {
107 q->tail = (q->tail - 1) & q->tab_mask;
108 if (q->head == q->tail)
109 break;
110 } while (q->tab[q->tail] == NULL);
111 }
112
113 /* Drop packet from queue array by creating a "hole" */
choke_drop_by_idx(struct Qdisc * sch,unsigned int idx,struct sk_buff ** to_free)114 static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
115 struct sk_buff **to_free)
116 {
117 struct choke_sched_data *q = qdisc_priv(sch);
118 struct sk_buff *skb = q->tab[idx];
119
120 q->tab[idx] = NULL;
121
122 if (idx == q->head)
123 choke_zap_head_holes(q);
124 if (idx == q->tail)
125 choke_zap_tail_holes(q);
126
127 qdisc_qstats_backlog_dec(sch, skb);
128 qdisc_tree_reduce_backlog(sch, 1, qdisc_pkt_len(skb));
129 qdisc_drop(skb, sch, to_free);
130 --sch->q.qlen;
131 }
132
133 struct choke_skb_cb {
134 u8 keys_valid;
135 struct flow_keys_digest keys;
136 };
137
choke_skb_cb(const struct sk_buff * skb)138 static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
139 {
140 qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
141 return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
142 }
143
144 /*
145 * Compare flow of two packets
146 * Returns true only if source and destination address and port match.
147 * false for special cases
148 */
choke_match_flow(struct sk_buff * skb1,struct sk_buff * skb2)149 static bool choke_match_flow(struct sk_buff *skb1,
150 struct sk_buff *skb2)
151 {
152 struct flow_keys temp;
153
154 if (skb1->protocol != skb2->protocol)
155 return false;
156
157 if (!choke_skb_cb(skb1)->keys_valid) {
158 choke_skb_cb(skb1)->keys_valid = 1;
159 skb_flow_dissect_flow_keys(skb1, &temp, 0);
160 make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
161 }
162
163 if (!choke_skb_cb(skb2)->keys_valid) {
164 choke_skb_cb(skb2)->keys_valid = 1;
165 skb_flow_dissect_flow_keys(skb2, &temp, 0);
166 make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
167 }
168
169 return !memcmp(&choke_skb_cb(skb1)->keys,
170 &choke_skb_cb(skb2)->keys,
171 sizeof(choke_skb_cb(skb1)->keys));
172 }
173
174 /*
175 * Select a packet at random from queue
176 * HACK: since queue can have holes from previous deletion; retry several
177 * times to find a random skb but then just give up and return the head
178 * Will return NULL if queue is empty (q->head == q->tail)
179 */
choke_peek_random(const struct choke_sched_data * q,unsigned int * pidx)180 static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
181 unsigned int *pidx)
182 {
183 struct sk_buff *skb;
184 int retrys = 3;
185
186 do {
187 *pidx = (q->head + prandom_u32_max(choke_len(q))) & q->tab_mask;
188 skb = q->tab[*pidx];
189 if (skb)
190 return skb;
191 } while (--retrys > 0);
192
193 return q->tab[*pidx = q->head];
194 }
195
196 /*
197 * Compare new packet with random packet in queue
198 * returns true if matched and sets *pidx
199 */
choke_match_random(const struct choke_sched_data * q,struct sk_buff * nskb,unsigned int * pidx)200 static bool choke_match_random(const struct choke_sched_data *q,
201 struct sk_buff *nskb,
202 unsigned int *pidx)
203 {
204 struct sk_buff *oskb;
205
206 if (q->head == q->tail)
207 return false;
208
209 oskb = choke_peek_random(q, pidx);
210 return choke_match_flow(oskb, nskb);
211 }
212
choke_enqueue(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)213 static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
214 struct sk_buff **to_free)
215 {
216 struct choke_sched_data *q = qdisc_priv(sch);
217 const struct red_parms *p = &q->parms;
218
219 choke_skb_cb(skb)->keys_valid = 0;
220 /* Compute average queue usage (see RED) */
221 q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
222 if (red_is_idling(&q->vars))
223 red_end_of_idle_period(&q->vars);
224
225 /* Is queue small? */
226 if (q->vars.qavg <= p->qth_min)
227 q->vars.qcount = -1;
228 else {
229 unsigned int idx;
230
231 /* Draw a packet at random from queue and compare flow */
232 if (choke_match_random(q, skb, &idx)) {
233 q->stats.matched++;
234 choke_drop_by_idx(sch, idx, to_free);
235 goto congestion_drop;
236 }
237
238 /* Queue is large, always mark/drop */
239 if (q->vars.qavg > p->qth_max) {
240 q->vars.qcount = -1;
241
242 qdisc_qstats_overlimit(sch);
243 if (use_harddrop(q) || !use_ecn(q) ||
244 !INET_ECN_set_ce(skb)) {
245 q->stats.forced_drop++;
246 goto congestion_drop;
247 }
248
249 q->stats.forced_mark++;
250 } else if (++q->vars.qcount) {
251 if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
252 q->vars.qcount = 0;
253 q->vars.qR = red_random(p);
254
255 qdisc_qstats_overlimit(sch);
256 if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
257 q->stats.prob_drop++;
258 goto congestion_drop;
259 }
260
261 q->stats.prob_mark++;
262 }
263 } else
264 q->vars.qR = red_random(p);
265 }
266
267 /* Admit new packet */
268 if (sch->q.qlen < q->limit) {
269 q->tab[q->tail] = skb;
270 q->tail = (q->tail + 1) & q->tab_mask;
271 ++sch->q.qlen;
272 qdisc_qstats_backlog_inc(sch, skb);
273 return NET_XMIT_SUCCESS;
274 }
275
276 q->stats.pdrop++;
277 return qdisc_drop(skb, sch, to_free);
278
279 congestion_drop:
280 qdisc_drop(skb, sch, to_free);
281 return NET_XMIT_CN;
282 }
283
choke_dequeue(struct Qdisc * sch)284 static struct sk_buff *choke_dequeue(struct Qdisc *sch)
285 {
286 struct choke_sched_data *q = qdisc_priv(sch);
287 struct sk_buff *skb;
288
289 if (q->head == q->tail) {
290 if (!red_is_idling(&q->vars))
291 red_start_of_idle_period(&q->vars);
292 return NULL;
293 }
294
295 skb = q->tab[q->head];
296 q->tab[q->head] = NULL;
297 choke_zap_head_holes(q);
298 --sch->q.qlen;
299 qdisc_qstats_backlog_dec(sch, skb);
300 qdisc_bstats_update(sch, skb);
301
302 return skb;
303 }
304
choke_reset(struct Qdisc * sch)305 static void choke_reset(struct Qdisc *sch)
306 {
307 struct choke_sched_data *q = qdisc_priv(sch);
308
309 while (q->head != q->tail) {
310 struct sk_buff *skb = q->tab[q->head];
311
312 q->head = (q->head + 1) & q->tab_mask;
313 if (!skb)
314 continue;
315 rtnl_qdisc_drop(skb, sch);
316 }
317
318 sch->q.qlen = 0;
319 sch->qstats.backlog = 0;
320 if (q->tab)
321 memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
322 q->head = q->tail = 0;
323 red_restart(&q->vars);
324 }
325
326 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
327 [TCA_CHOKE_PARMS] = { .len = sizeof(struct tc_red_qopt) },
328 [TCA_CHOKE_STAB] = { .len = RED_STAB_SIZE },
329 [TCA_CHOKE_MAX_P] = { .type = NLA_U32 },
330 };
331
332
choke_free(void * addr)333 static void choke_free(void *addr)
334 {
335 kvfree(addr);
336 }
337
choke_change(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)338 static int choke_change(struct Qdisc *sch, struct nlattr *opt,
339 struct netlink_ext_ack *extack)
340 {
341 struct choke_sched_data *q = qdisc_priv(sch);
342 struct nlattr *tb[TCA_CHOKE_MAX + 1];
343 const struct tc_red_qopt *ctl;
344 int err;
345 struct sk_buff **old = NULL;
346 unsigned int mask;
347 u32 max_P;
348
349 if (opt == NULL)
350 return -EINVAL;
351
352 err = nla_parse_nested_deprecated(tb, TCA_CHOKE_MAX, opt,
353 choke_policy, NULL);
354 if (err < 0)
355 return err;
356
357 if (tb[TCA_CHOKE_PARMS] == NULL ||
358 tb[TCA_CHOKE_STAB] == NULL)
359 return -EINVAL;
360
361 max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
362
363 ctl = nla_data(tb[TCA_CHOKE_PARMS]);
364
365 if (!red_check_params(ctl->qth_min, ctl->qth_max, ctl->Wlog))
366 return -EINVAL;
367
368 if (ctl->limit > CHOKE_MAX_QUEUE)
369 return -EINVAL;
370
371 mask = roundup_pow_of_two(ctl->limit + 1) - 1;
372 if (mask != q->tab_mask) {
373 struct sk_buff **ntab;
374
375 ntab = kvcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
376 if (!ntab)
377 return -ENOMEM;
378
379 sch_tree_lock(sch);
380 old = q->tab;
381 if (old) {
382 unsigned int oqlen = sch->q.qlen, tail = 0;
383 unsigned dropped = 0;
384
385 while (q->head != q->tail) {
386 struct sk_buff *skb = q->tab[q->head];
387
388 q->head = (q->head + 1) & q->tab_mask;
389 if (!skb)
390 continue;
391 if (tail < mask) {
392 ntab[tail++] = skb;
393 continue;
394 }
395 dropped += qdisc_pkt_len(skb);
396 qdisc_qstats_backlog_dec(sch, skb);
397 --sch->q.qlen;
398 rtnl_qdisc_drop(skb, sch);
399 }
400 qdisc_tree_reduce_backlog(sch, oqlen - sch->q.qlen, dropped);
401 q->head = 0;
402 q->tail = tail;
403 }
404
405 q->tab_mask = mask;
406 q->tab = ntab;
407 } else
408 sch_tree_lock(sch);
409
410 q->flags = ctl->flags;
411 q->limit = ctl->limit;
412
413 red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
414 ctl->Plog, ctl->Scell_log,
415 nla_data(tb[TCA_CHOKE_STAB]),
416 max_P);
417 red_set_vars(&q->vars);
418
419 if (q->head == q->tail)
420 red_end_of_idle_period(&q->vars);
421
422 sch_tree_unlock(sch);
423 choke_free(old);
424 return 0;
425 }
426
choke_init(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)427 static int choke_init(struct Qdisc *sch, struct nlattr *opt,
428 struct netlink_ext_ack *extack)
429 {
430 return choke_change(sch, opt, extack);
431 }
432
choke_dump(struct Qdisc * sch,struct sk_buff * skb)433 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
434 {
435 struct choke_sched_data *q = qdisc_priv(sch);
436 struct nlattr *opts = NULL;
437 struct tc_red_qopt opt = {
438 .limit = q->limit,
439 .flags = q->flags,
440 .qth_min = q->parms.qth_min >> q->parms.Wlog,
441 .qth_max = q->parms.qth_max >> q->parms.Wlog,
442 .Wlog = q->parms.Wlog,
443 .Plog = q->parms.Plog,
444 .Scell_log = q->parms.Scell_log,
445 };
446
447 opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
448 if (opts == NULL)
449 goto nla_put_failure;
450
451 if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
452 nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
453 goto nla_put_failure;
454 return nla_nest_end(skb, opts);
455
456 nla_put_failure:
457 nla_nest_cancel(skb, opts);
458 return -EMSGSIZE;
459 }
460
choke_dump_stats(struct Qdisc * sch,struct gnet_dump * d)461 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
462 {
463 struct choke_sched_data *q = qdisc_priv(sch);
464 struct tc_choke_xstats st = {
465 .early = q->stats.prob_drop + q->stats.forced_drop,
466 .marked = q->stats.prob_mark + q->stats.forced_mark,
467 .pdrop = q->stats.pdrop,
468 .other = q->stats.other,
469 .matched = q->stats.matched,
470 };
471
472 return gnet_stats_copy_app(d, &st, sizeof(st));
473 }
474
choke_destroy(struct Qdisc * sch)475 static void choke_destroy(struct Qdisc *sch)
476 {
477 struct choke_sched_data *q = qdisc_priv(sch);
478
479 choke_free(q->tab);
480 }
481
choke_peek_head(struct Qdisc * sch)482 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
483 {
484 struct choke_sched_data *q = qdisc_priv(sch);
485
486 return (q->head != q->tail) ? q->tab[q->head] : NULL;
487 }
488
489 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
490 .id = "choke",
491 .priv_size = sizeof(struct choke_sched_data),
492
493 .enqueue = choke_enqueue,
494 .dequeue = choke_dequeue,
495 .peek = choke_peek_head,
496 .init = choke_init,
497 .destroy = choke_destroy,
498 .reset = choke_reset,
499 .change = choke_change,
500 .dump = choke_dump,
501 .dump_stats = choke_dump_stats,
502 .owner = THIS_MODULE,
503 };
504
choke_module_init(void)505 static int __init choke_module_init(void)
506 {
507 return register_qdisc(&choke_qdisc_ops);
508 }
509
choke_module_exit(void)510 static void __exit choke_module_exit(void)
511 {
512 unregister_qdisc(&choke_qdisc_ops);
513 }
514
515 module_init(choke_module_init)
516 module_exit(choke_module_exit)
517
518 MODULE_LICENSE("GPL");
519
