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 {
 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_drop(skb, sch);
 132         qdisc_tree_decrease_qlen(sch, 1);
 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         memset(q->tab, 0, (q->tab_mask + 1) * sizeof(struct sk_buff *));
 400         q->head = q->tail = 0;
 401         red_restart(&q->vars);
 402 }
 403
 404 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
 405         [TCA_CHOKE_PARMS]       = { .len = sizeof(struct tc_red_qopt) },
 406         [TCA_CHOKE_STAB]        = { .len = RED_STAB_SIZE },
 407         [TCA_CHOKE_MAX_P]       = { .type = NLA_U32 },
 408 };
 409
 410
 411 static void choke_free(void *addr)
 412 {
 413         kvfree(addr);
 414 }
 415
 416 static int choke_change(struct Qdisc *sch, struct nlattr *opt)
 417 {
 418         struct choke_sched_data *q = qdisc_priv(sch);
 419         struct nlattr *tb[TCA_CHOKE_MAX + 1];
 420         const struct tc_red_qopt *ctl;
 421         int err;
 422         struct sk_buff **old = NULL;
 423         unsigned int mask;
 424         u32 max_P;
 425
 426         if (opt == NULL)
 427                 return -EINVAL;
 428
 429         err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
 430         if (err < 0)
 431                 return err;
 432
 433         if (tb[TCA_CHOKE_PARMS] == NULL ||
 434             tb[TCA_CHOKE_STAB] == NULL)
 435                 return -EINVAL;
 436
 437         max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
 438
 439         ctl = nla_data(tb[TCA_CHOKE_PARMS]);
 440
 441         if (ctl->limit > CHOKE_MAX_QUEUE)
 442                 return -EINVAL;
 443
 444         mask = roundup_pow_of_two(ctl->limit + 1) - 1;
 445         if (mask != q->tab_mask) {
 446                 struct sk_buff **ntab;
 447
 448                 ntab = kcalloc(mask + 1, sizeof(struct sk_buff *),
 449                                GFP_KERNEL | __GFP_NOWARN);
 450                 if (!ntab)
 451                         ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
 452                 if (!ntab)
 453                         return -ENOMEM;
 454
 455                 sch_tree_lock(sch);
 456                 old = q->tab;
 457                 if (old) {
 458                         unsigned int oqlen = sch->q.qlen, tail = 0;
 459
 460                         while (q->head != q->tail) {
 461                                 struct sk_buff *skb = q->tab[q->head];
 462
 463                                 q->head = (q->head + 1) & q->tab_mask;
 464                                 if (!skb)
 465                                         continue;
 466                                 if (tail < mask) {
 467                                         ntab[tail++] = skb;
 468                                         continue;
 469                                 }
 470                                 qdisc_qstats_backlog_dec(sch, skb);
 471                                 --sch->q.qlen;
 472                                 qdisc_drop(skb, sch);
 473                         }
 474                         qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
 475                         q->head = 0;
 476                         q->tail = tail;
 477                 }
 478
 479                 q->tab_mask = mask;
 480                 q->tab = ntab;
 481         } else
 482                 sch_tree_lock(sch);
 483
 484         q->flags = ctl->flags;
 485         q->limit = ctl->limit;
 486
 487         red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
 488                       ctl->Plog, ctl->Scell_log,
 489                       nla_data(tb[TCA_CHOKE_STAB]),
 490                       max_P);
 491         red_set_vars(&q->vars);
 492
 493         if (q->head == q->tail)
 494                 red_end_of_idle_period(&q->vars);
 495
 496         sch_tree_unlock(sch);
 497         choke_free(old);
 498         return 0;
 499 }
 500
 501 static int choke_init(struct Qdisc *sch, struct nlattr *opt)
 502 {
 503         return choke_change(sch, opt);
 504 }
 505
 506 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
 507 {
 508         struct choke_sched_data *q = qdisc_priv(sch);
 509         struct nlattr *opts = NULL;
 510         struct tc_red_qopt opt = {
 511                 .limit          = q->limit,
 512                 .flags          = q->flags,
 513                 .qth_min        = q->parms.qth_min >> q->parms.Wlog,
 514                 .qth_max        = q->parms.qth_max >> q->parms.Wlog,
 515                 .Wlog           = q->parms.Wlog,
 516                 .Plog           = q->parms.Plog,
 517                 .Scell_log      = q->parms.Scell_log,
 518         };
 519
 520         opts = nla_nest_start(skb, TCA_OPTIONS);
 521         if (opts == NULL)
 522                 goto nla_put_failure;
 523
 524         if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
 525             nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
 526                 goto nla_put_failure;
 527         return nla_nest_end(skb, opts);
 528
 529 nla_put_failure:
 530         nla_nest_cancel(skb, opts);
 531         return -EMSGSIZE;
 532 }
 533
 534 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 535 {
 536         struct choke_sched_data *q = qdisc_priv(sch);
 537         struct tc_choke_xstats st = {
 538                 .early  = q->stats.prob_drop + q->stats.forced_drop,
 539                 .marked = q->stats.prob_mark + q->stats.forced_mark,
 540                 .pdrop  = q->stats.pdrop,
 541                 .other  = q->stats.other,
 542                 .matched = q->stats.matched,
 543         };
 544
 545         return gnet_stats_copy_app(d, &st, sizeof(st));
 546 }
 547
 548 static void choke_destroy(struct Qdisc *sch)
 549 {
 550         struct choke_sched_data *q = qdisc_priv(sch);
 551
 552         tcf_destroy_chain(&q->filter_list);
 553         choke_free(q->tab);
 554 }
 555
 556 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
 557 {
 558         struct choke_sched_data *q = qdisc_priv(sch);
 559
 560         return (q->head != q->tail) ? q->tab[q->head] : NULL;
 561 }
 562
 563 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
 564         .id             =       "choke",
 565         .priv_size      =       sizeof(struct choke_sched_data),
 566
 567         .enqueue        =       choke_enqueue,
 568         .dequeue        =       choke_dequeue,
 569         .peek           =       choke_peek_head,
 570         .drop           =       choke_drop,
 571         .init           =       choke_init,
 572         .destroy        =       choke_destroy,
 573         .reset          =       choke_reset,
 574         .change         =       choke_change,
 575         .dump           =       choke_dump,
 576         .dump_stats     =       choke_dump_stats,
 577         .owner          =       THIS_MODULE,
 578 };
 579
 580 static int __init choke_module_init(void)
 581 {
 582         return register_qdisc(&choke_qdisc_ops);
 583 }
 584
 585 static void __exit choke_module_exit(void)
 586 {
 587         unregister_qdisc(&choke_qdisc_ops);
 588 }
 589
 590 module_init(choke_module_init)
 591 module_exit(choke_module_exit)
 592
 593 MODULE_LICENSE("GPL");