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 matched; /* Drops to flow match */
64 } stats;
65
66 unsigned int head;
67 unsigned int tail;
68
69 unsigned int tab_mask; /* size - 1 */
70
71 struct sk_buff **tab;
72 };
73
74 /* number of elements in queue including holes */
choke_len(const struct choke_sched_data * q)75 static unsigned int choke_len(const struct choke_sched_data *q)
76 {
77 return (q->tail - q->head) & q->tab_mask;
78 }
79
80 /* Is ECN parameter configured */
use_ecn(const struct choke_sched_data * q)81 static int use_ecn(const struct choke_sched_data *q)
82 {
83 return q->flags & TC_RED_ECN;
84 }
85
86 /* Should packets over max just be dropped (versus marked) */
use_harddrop(const struct choke_sched_data * q)87 static int use_harddrop(const struct choke_sched_data *q)
88 {
89 return q->flags & TC_RED_HARDDROP;
90 }
91
92 /* Move head pointer forward to skip over holes */
choke_zap_head_holes(struct choke_sched_data * q)93 static void choke_zap_head_holes(struct choke_sched_data *q)
94 {
95 do {
96 q->head = (q->head + 1) & q->tab_mask;
97 if (q->head == q->tail)
98 break;
99 } while (q->tab[q->head] == NULL);
100 }
101
102 /* Move tail pointer backwards to reuse holes */
choke_zap_tail_holes(struct choke_sched_data * q)103 static void choke_zap_tail_holes(struct choke_sched_data *q)
104 {
105 do {
106 q->tail = (q->tail - 1) & q->tab_mask;
107 if (q->head == q->tail)
108 break;
109 } while (q->tab[q->tail] == NULL);
110 }
111
112 /* Drop packet from queue array by creating a "hole" */
choke_drop_by_idx(struct Qdisc * sch,unsigned int idx,struct sk_buff ** to_free)113 static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx,
114 struct sk_buff **to_free)
115 {
116 struct choke_sched_data *q = qdisc_priv(sch);
117 struct sk_buff *skb = q->tab[idx];
118
119 q->tab[idx] = NULL;
120
121 if (idx == q->head)
122 choke_zap_head_holes(q);
123 if (idx == q->tail)
124 choke_zap_tail_holes(q);
125
126 --sch->q.qlen;
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 }
131
132 struct choke_skb_cb {
133 u8 keys_valid;
134 struct flow_keys_digest keys;
135 };
136
choke_skb_cb(const struct sk_buff * skb)137 static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
138 {
139 qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
140 return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
141 }
142
143 /*
144 * Compare flow of two packets
145 * Returns true only if source and destination address and port match.
146 * false for special cases
147 */
choke_match_flow(struct sk_buff * skb1,struct sk_buff * skb2)148 static bool choke_match_flow(struct sk_buff *skb1,
149 struct sk_buff *skb2)
150 {
151 struct flow_keys temp;
152
153 if (skb1->protocol != skb2->protocol)
154 return false;
155
156 if (!choke_skb_cb(skb1)->keys_valid) {
157 choke_skb_cb(skb1)->keys_valid = 1;
158 skb_flow_dissect_flow_keys(skb1, &temp, 0);
159 make_flow_keys_digest(&choke_skb_cb(skb1)->keys, &temp);
160 }
161
162 if (!choke_skb_cb(skb2)->keys_valid) {
163 choke_skb_cb(skb2)->keys_valid = 1;
164 skb_flow_dissect_flow_keys(skb2, &temp, 0);
165 make_flow_keys_digest(&choke_skb_cb(skb2)->keys, &temp);
166 }
167
168 return !memcmp(&choke_skb_cb(skb1)->keys,
169 &choke_skb_cb(skb2)->keys,
170 sizeof(choke_skb_cb(skb1)->keys));
171 }
172
173 /*
174 * Select a packet at random from queue
175 * HACK: since queue can have holes from previous deletion; retry several
176 * times to find a random skb but then just give up and return the head
177 * Will return NULL if queue is empty (q->head == q->tail)
178 */
choke_peek_random(const struct choke_sched_data * q,unsigned int * pidx)179 static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
180 unsigned int *pidx)
181 {
182 struct sk_buff *skb;
183 int retrys = 3;
184
185 do {
186 *pidx = (q->head + get_random_u32_below(choke_len(q))) & q->tab_mask;
187 skb = q->tab[*pidx];
188 if (skb)
189 return skb;
190 } while (--retrys > 0);
191
192 return q->tab[*pidx = q->head];
193 }
194
195 /*
196 * Compare new packet with random packet in queue
197 * returns true if matched and sets *pidx
198 */
choke_match_random(const struct choke_sched_data * q,struct sk_buff * nskb,unsigned int * pidx)199 static bool choke_match_random(const struct choke_sched_data *q,
200 struct sk_buff *nskb,
201 unsigned int *pidx)
202 {
203 struct sk_buff *oskb;
204
205 if (q->head == q->tail)
206 return false;
207
208 oskb = choke_peek_random(q, pidx);
209 return choke_match_flow(oskb, nskb);
210 }
211
choke_enqueue(struct sk_buff * skb,struct Qdisc * sch,struct sk_buff ** to_free)212 static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch,
213 struct sk_buff **to_free)
214 {
215 struct choke_sched_data *q = qdisc_priv(sch);
216 const struct red_parms *p = &q->parms;
217
218 choke_skb_cb(skb)->keys_valid = 0;
219 /* Compute average queue usage (see RED) */
220 q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
221 if (red_is_idling(&q->vars))
222 red_end_of_idle_period(&q->vars);
223
224 /* Is queue small? */
225 if (q->vars.qavg <= p->qth_min)
226 q->vars.qcount = -1;
227 else {
228 unsigned int idx;
229
230 /* Draw a packet at random from queue and compare flow */
231 if (choke_match_random(q, skb, &idx)) {
232 q->stats.matched++;
233 choke_drop_by_idx(sch, idx, to_free);
234 goto congestion_drop;
235 }
236
237 /* Queue is large, always mark/drop */
238 if (q->vars.qavg > p->qth_max) {
239 q->vars.qcount = -1;
240
241 qdisc_qstats_overlimit(sch);
242 if (use_harddrop(q) || !use_ecn(q) ||
243 !INET_ECN_set_ce(skb)) {
244 q->stats.forced_drop++;
245 goto congestion_drop;
246 }
247
248 q->stats.forced_mark++;
249 } else if (++q->vars.qcount) {
250 if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
251 q->vars.qcount = 0;
252 q->vars.qR = red_random(p);
253
254 qdisc_qstats_overlimit(sch);
255 if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
256 q->stats.prob_drop++;
257 goto congestion_drop;
258 }
259
260 q->stats.prob_mark++;
261 }
262 } else
263 q->vars.qR = red_random(p);
264 }
265
266 /* Admit new packet */
267 if (sch->q.qlen < q->limit) {
268 q->tab[q->tail] = skb;
269 q->tail = (q->tail + 1) & q->tab_mask;
270 ++sch->q.qlen;
271 qdisc_qstats_backlog_inc(sch, skb);
272 return NET_XMIT_SUCCESS;
273 }
274
275 q->stats.pdrop++;
276 return qdisc_drop(skb, sch, to_free);
277
278 congestion_drop:
279 qdisc_drop(skb, sch, to_free);
280 return NET_XMIT_CN;
281 }
282
choke_dequeue(struct Qdisc * sch)283 static struct sk_buff *choke_dequeue(struct Qdisc *sch)
284 {
285 struct choke_sched_data *q = qdisc_priv(sch);
286 struct sk_buff *skb;
287
288 if (q->head == q->tail) {
289 if (!red_is_idling(&q->vars))
290 red_start_of_idle_period(&q->vars);
291 return NULL;
292 }
293
294 skb = q->tab[q->head];
295 q->tab[q->head] = NULL;
296 choke_zap_head_holes(q);
297 --sch->q.qlen;
298 qdisc_qstats_backlog_dec(sch, skb);
299 qdisc_bstats_update(sch, skb);
300
301 return skb;
302 }
303
choke_reset(struct Qdisc * sch)304 static void choke_reset(struct Qdisc *sch)
305 {
306 struct choke_sched_data *q = qdisc_priv(sch);
307
308 while (q->head != q->tail) {
309 struct sk_buff *skb = q->tab[q->head];
310
311 q->head = (q->head + 1) & q->tab_mask;
312 if (!skb)
313 continue;
314 rtnl_qdisc_drop(skb, sch);
315 }
316
317 if (q->tab)
318 memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
319 q->head = q->tail = 0;
320 red_restart(&q->vars);
321 }
322
323 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
324 [TCA_CHOKE_PARMS] = { .len = sizeof(struct tc_red_qopt) },
325 [TCA_CHOKE_STAB] = { .len = RED_STAB_SIZE },
326 [TCA_CHOKE_MAX_P] = { .type = NLA_U32 },
327 };
328
329
choke_free(void * addr)330 static void choke_free(void *addr)
331 {
332 kvfree(addr);
333 }
334
choke_change(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)335 static int choke_change(struct Qdisc *sch, struct nlattr *opt,
336 struct netlink_ext_ack *extack)
337 {
338 struct choke_sched_data *q = qdisc_priv(sch);
339 struct nlattr *tb[TCA_CHOKE_MAX + 1];
340 const struct tc_red_qopt *ctl;
341 int err;
342 struct sk_buff **old = NULL;
343 unsigned int mask;
344 u32 max_P;
345 u8 *stab;
346
347 if (opt == NULL)
348 return -EINVAL;
349
350 err = nla_parse_nested_deprecated(tb, TCA_CHOKE_MAX, opt,
351 choke_policy, NULL);
352 if (err < 0)
353 return err;
354
355 if (tb[TCA_CHOKE_PARMS] == NULL ||
356 tb[TCA_CHOKE_STAB] == NULL)
357 return -EINVAL;
358
359 max_P = nla_get_u32_default(tb[TCA_CHOKE_MAX_P], 0);
360
361 ctl = nla_data(tb[TCA_CHOKE_PARMS]);
362 stab = nla_data(tb[TCA_CHOKE_STAB]);
363 if (!red_check_params(ctl->qth_min, ctl->qth_max, ctl->Wlog, ctl->Scell_log, stab))
364 return -EINVAL;
365
366 if (ctl->limit > CHOKE_MAX_QUEUE)
367 return -EINVAL;
368
369 mask = roundup_pow_of_two(ctl->limit + 1) - 1;
370 if (mask != q->tab_mask) {
371 struct sk_buff **ntab;
372
373 ntab = kvcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
374 if (!ntab)
375 return -ENOMEM;
376
377 sch_tree_lock(sch);
378 old = q->tab;
379 if (old) {
380 unsigned int oqlen = sch->q.qlen, tail = 0;
381 unsigned dropped = 0;
382
383 while (q->head != q->tail) {
384 struct sk_buff *skb = q->tab[q->head];
385
386 q->head = (q->head + 1) & q->tab_mask;
387 if (!skb)
388 continue;
389 if (tail < mask) {
390 ntab[tail++] = skb;
391 continue;
392 }
393 dropped += qdisc_pkt_len(skb);
394 qdisc_qstats_backlog_dec(sch, skb);
395 --sch->q.qlen;
396 rtnl_qdisc_drop(skb, sch);
397 }
398 qdisc_tree_reduce_backlog(sch, oqlen - sch->q.qlen, dropped);
399 q->head = 0;
400 q->tail = tail;
401 }
402
403 q->tab_mask = mask;
404 q->tab = ntab;
405 } else
406 sch_tree_lock(sch);
407
408 WRITE_ONCE(q->flags, ctl->flags);
409 WRITE_ONCE(q->limit, ctl->limit);
410
411 red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
412 ctl->Plog, ctl->Scell_log,
413 stab,
414 max_P);
415 red_set_vars(&q->vars);
416
417 if (q->head == q->tail)
418 red_end_of_idle_period(&q->vars);
419
420 sch_tree_unlock(sch);
421 choke_free(old);
422 return 0;
423 }
424
choke_init(struct Qdisc * sch,struct nlattr * opt,struct netlink_ext_ack * extack)425 static int choke_init(struct Qdisc *sch, struct nlattr *opt,
426 struct netlink_ext_ack *extack)
427 {
428 return choke_change(sch, opt, extack);
429 }
430
choke_dump(struct Qdisc * sch,struct sk_buff * skb)431 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
432 {
433 struct choke_sched_data *q = qdisc_priv(sch);
434 u8 Wlog = READ_ONCE(q->parms.Wlog);
435 struct nlattr *opts = NULL;
436 struct tc_red_qopt opt = {
437 .limit = READ_ONCE(q->limit),
438 .flags = READ_ONCE(q->flags),
439 .qth_min = READ_ONCE(q->parms.qth_min) >> Wlog,
440 .qth_max = READ_ONCE(q->parms.qth_max) >> Wlog,
441 .Wlog = Wlog,
442 .Plog = READ_ONCE(q->parms.Plog),
443 .Scell_log = READ_ONCE(q->parms.Scell_log),
444 };
445
446 opts = nla_nest_start_noflag(skb, TCA_OPTIONS);
447 if (opts == NULL)
448 goto nla_put_failure;
449
450 if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
451 nla_put_u32(skb, TCA_CHOKE_MAX_P, READ_ONCE(q->parms.max_P)))
452 goto nla_put_failure;
453 return nla_nest_end(skb, opts);
454
455 nla_put_failure:
456 nla_nest_cancel(skb, opts);
457 return -EMSGSIZE;
458 }
459
choke_dump_stats(struct Qdisc * sch,struct gnet_dump * d)460 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
461 {
462 struct choke_sched_data *q = qdisc_priv(sch);
463 struct tc_choke_xstats st = {
464 .early = q->stats.prob_drop + q->stats.forced_drop,
465 .marked = q->stats.prob_mark + q->stats.forced_mark,
466 .pdrop = q->stats.pdrop,
467 .matched = q->stats.matched,
468 };
469
470 return gnet_stats_copy_app(d, &st, sizeof(st));
471 }
472
choke_destroy(struct Qdisc * sch)473 static void choke_destroy(struct Qdisc *sch)
474 {
475 struct choke_sched_data *q = qdisc_priv(sch);
476
477 choke_free(q->tab);
478 }
479
choke_peek_head(struct Qdisc * sch)480 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
481 {
482 struct choke_sched_data *q = qdisc_priv(sch);
483
484 return (q->head != q->tail) ? q->tab[q->head] : NULL;
485 }
486
487 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
488 .id = "choke",
489 .priv_size = sizeof(struct choke_sched_data),
490
491 .enqueue = choke_enqueue,
492 .dequeue = choke_dequeue,
493 .peek = choke_peek_head,
494 .init = choke_init,
495 .destroy = choke_destroy,
496 .reset = choke_reset,
497 .change = choke_change,
498 .dump = choke_dump,
499 .dump_stats = choke_dump_stats,
500 .owner = THIS_MODULE,
501 };
502 MODULE_ALIAS_NET_SCH("choke");
503
choke_module_init(void)504 static int __init choke_module_init(void)
505 {
506 return register_qdisc(&choke_qdisc_ops);
507 }
508
choke_module_exit(void)509 static void __exit choke_module_exit(void)
510 {
511 unregister_qdisc(&choke_qdisc_ops);
512 }
513
514 module_init(choke_module_init)
515 module_exit(choke_module_exit)
516
517 MODULE_LICENSE("GPL");
518 MODULE_DESCRIPTION("Choose and keep responsive flows scheduler");
519