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/reciprocal_div.h>
  18 #include <linux/vmalloc.h>
  19 #include <net/pkt_sched.h>
  20 #include <net/inet_ecn.h>
  21 #include <net/red.h>
  22 #include <linux/ip.h>
  23 #include <net/ip.h>
  24 #include <linux/ipv6.h>
  25 #include <net/ipv6.h>
  26
  27 /*
  28    CHOKe stateless AQM for fair bandwidth allocation
  29    =================================================
  30
  31    CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
  32    unresponsive flows) is a variant of RED that penalizes misbehaving flows but
  33    maintains no flow state. The difference from RED is an additional step
  34    during the enqueuing process. If average queue size is over the
  35    low threshold (qmin), a packet is chosen at random from the queue.
  36    If both the new and chosen packet are from the same flow, both
  37    are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
  38    needs to access packets in queue randomly. It has a minimal class
  39    interface to allow overriding the builtin flow classifier with
  40    filters.
  41
  42    Source:
  43    R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
  44    Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
  45    IEEE INFOCOM, 2000.
  46
  47    A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
  48    Characteristics", IEEE/ACM Transactions on Networking, 2004
  49
  50  */
  51
  52 /* Upper bound on size of sk_buff table (packets) */
  53 #define CHOKE_MAX_QUEUE (128*1024 - 1)
  54
  55 struct choke_sched_data {
  56 /* Parameters */
  57         u32              limit;
  58         unsigned char    flags;
  59
  60         struct red_parms parms;
  61
  62 /* Variables */
  63         struct tcf_proto *filter_list;
  64         struct {
  65                 u32     prob_drop;      /* Early probability drops */
  66                 u32     prob_mark;      /* Early probability marks */
  67                 u32     forced_drop;    /* Forced drops, qavg > max_thresh */
  68                 u32     forced_mark;    /* Forced marks, qavg > max_thresh */
  69                 u32     pdrop;          /* Drops due to queue limits */
  70                 u32     other;          /* Drops due to drop() calls */
  71                 u32     matched;        /* Drops to flow match */
  72         } stats;
  73
  74         unsigned int     head;
  75         unsigned int     tail;
  76
  77         unsigned int     tab_mask; /* size - 1 */
  78
  79         struct sk_buff **tab;
  80 };
  81
  82 /* deliver a random number between 0 and N - 1 */
  83 static u32 random_N(unsigned int N)
  84 {
  85         return reciprocal_divide(random32(), N);
  86 }
  87
  88 /* number of elements in queue including holes */
  89 static unsigned int choke_len(const struct choke_sched_data *q)
  90 {
  91         return (q->tail - q->head) & q->tab_mask;
  92 }
  93
  94 /* Is ECN parameter configured */
  95 static int use_ecn(const struct choke_sched_data *q)
  96 {
  97         return q->flags & TC_RED_ECN;
  98 }
  99
 100 /* Should packets over max just be dropped (versus marked) */
 101 static int use_harddrop(const struct choke_sched_data *q)
 102 {
 103         return q->flags & TC_RED_HARDDROP;
 104 }
 105
 106 /* Move head pointer forward to skip over holes */
 107 static void choke_zap_head_holes(struct choke_sched_data *q)
 108 {
 109         do {
 110                 q->head = (q->head + 1) & q->tab_mask;
 111                 if (q->head == q->tail)
 112                         break;
 113         } while (q->tab[q->head] == NULL);
 114 }
 115
 116 /* Move tail pointer backwards to reuse holes */
 117 static void choke_zap_tail_holes(struct choke_sched_data *q)
 118 {
 119         do {
 120                 q->tail = (q->tail - 1) & q->tab_mask;
 121                 if (q->head == q->tail)
 122                         break;
 123         } while (q->tab[q->tail] == NULL);
 124 }
 125
 126 /* Drop packet from queue array by creating a "hole" */
 127 static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx)
 128 {
 129         struct choke_sched_data *q = qdisc_priv(sch);
 130         struct sk_buff *skb = q->tab[idx];
 131
 132         q->tab[idx] = NULL;
 133
 134         if (idx == q->head)
 135                 choke_zap_head_holes(q);
 136         if (idx == q->tail)
 137                 choke_zap_tail_holes(q);
 138
 139         sch->qstats.backlog -= qdisc_pkt_len(skb);
 140         qdisc_drop(skb, sch);
 141         qdisc_tree_decrease_qlen(sch, 1);
 142         --sch->q.qlen;
 143 }
 144
 145 /*
 146  * Compare flow of two packets
 147  *  Returns true only if source and destination address and port match.
 148  *          false for special cases
 149  */
 150 static bool choke_match_flow(struct sk_buff *skb1,
 151                              struct sk_buff *skb2)
 152 {
 153         int off1, off2, poff;
 154         const u32 *ports1, *ports2;
 155         u8 ip_proto;
 156         __u32 hash1;
 157
 158         if (skb1->protocol != skb2->protocol)
 159                 return false;
 160
 161         /* Use hash value as quick check
 162          * Assumes that __skb_get_rxhash makes IP header and ports linear
 163          */
 164         hash1 = skb_get_rxhash(skb1);
 165         if (!hash1 || hash1 != skb_get_rxhash(skb2))
 166                 return false;
 167
 168         /* Probably match, but be sure to avoid hash collisions */
 169         off1 = skb_network_offset(skb1);
 170         off2 = skb_network_offset(skb2);
 171
 172         switch (skb1->protocol) {
 173         case __constant_htons(ETH_P_IP): {
 174                 const struct iphdr *ip1, *ip2;
 175
 176                 ip1 = (const struct iphdr *) (skb1->data + off1);
 177                 ip2 = (const struct iphdr *) (skb2->data + off2);
 178
 179                 ip_proto = ip1->protocol;
 180                 if (ip_proto != ip2->protocol ||
 181                     ip1->saddr != ip2->saddr || ip1->daddr != ip2->daddr)
 182                         return false;
 183
 184                 if (ip_is_fragment(ip1) | ip_is_fragment(ip2))
 185                         ip_proto = 0;
 186                 off1 += ip1->ihl * 4;
 187                 off2 += ip2->ihl * 4;
 188                 break;
 189         }
 190
 191         case __constant_htons(ETH_P_IPV6): {
 192                 const struct ipv6hdr *ip1, *ip2;
 193
 194                 ip1 = (const struct ipv6hdr *) (skb1->data + off1);
 195                 ip2 = (const struct ipv6hdr *) (skb2->data + off2);
 196
 197                 ip_proto = ip1->nexthdr;
 198                 if (ip_proto != ip2->nexthdr ||
 199                     ipv6_addr_cmp(&ip1->saddr, &ip2->saddr) ||
 200                     ipv6_addr_cmp(&ip1->daddr, &ip2->daddr))
 201                         return false;
 202                 off1 += 40;
 203                 off2 += 40;
 204         }
 205
 206         default: /* Maybe compare MAC header here? */
 207                 return false;
 208         }
 209
 210         poff = proto_ports_offset(ip_proto);
 211         if (poff < 0)
 212                 return true;
 213
 214         off1 += poff;
 215         off2 += poff;
 216
 217         ports1 = (__force u32 *)(skb1->data + off1);
 218         ports2 = (__force u32 *)(skb2->data + off2);
 219         return *ports1 == *ports2;
 220 }
 221
 222 struct choke_skb_cb {
 223         u16 classid;
 224 };
 225
 226 static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
 227 {
 228         BUILD_BUG_ON(sizeof(skb->cb) <
 229                 sizeof(struct qdisc_skb_cb) + sizeof(struct choke_skb_cb));
 230         return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
 231 }
 232
 233 static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
 234 {
 235         choke_skb_cb(skb)->classid = classid;
 236 }
 237
 238 static u16 choke_get_classid(const struct sk_buff *skb)
 239 {
 240         return choke_skb_cb(skb)->classid;
 241 }
 242
 243 /*
 244  * Classify flow using either:
 245  *  1. pre-existing classification result in skb
 246  *  2. fast internal classification
 247  *  3. use TC filter based classification
 248  */
 249 static bool choke_classify(struct sk_buff *skb,
 250                            struct Qdisc *sch, int *qerr)
 251
 252 {
 253         struct choke_sched_data *q = qdisc_priv(sch);
 254         struct tcf_result res;
 255         int result;
 256
 257         result = tc_classify(skb, q->filter_list, &res);
 258         if (result >= 0) {
 259 #ifdef CONFIG_NET_CLS_ACT
 260                 switch (result) {
 261                 case TC_ACT_STOLEN:
 262                 case TC_ACT_QUEUED:
 263                         *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
 264                 case TC_ACT_SHOT:
 265                         return false;
 266                 }
 267 #endif
 268                 choke_set_classid(skb, TC_H_MIN(res.classid));
 269                 return true;
 270         }
 271
 272         return false;
 273 }
 274
 275 /*
 276  * Select a packet at random from queue
 277  * HACK: since queue can have holes from previous deletion; retry several
 278  *   times to find a random skb but then just give up and return the head
 279  * Will return NULL if queue is empty (q->head == q->tail)
 280  */
 281 static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
 282                                          unsigned int *pidx)
 283 {
 284         struct sk_buff *skb;
 285         int retrys = 3;
 286
 287         do {
 288                 *pidx = (q->head + random_N(choke_len(q))) & q->tab_mask;
 289                 skb = q->tab[*pidx];
 290                 if (skb)
 291                         return skb;
 292         } while (--retrys > 0);
 293
 294         return q->tab[*pidx = q->head];
 295 }
 296
 297 /*
 298  * Compare new packet with random packet in queue
 299  * returns true if matched and sets *pidx
 300  */
 301 static bool choke_match_random(const struct choke_sched_data *q,
 302                                struct sk_buff *nskb,
 303                                unsigned int *pidx)
 304 {
 305         struct sk_buff *oskb;
 306
 307         if (q->head == q->tail)
 308                 return false;
 309
 310         oskb = choke_peek_random(q, pidx);
 311         if (q->filter_list)
 312                 return choke_get_classid(nskb) == choke_get_classid(oskb);
 313
 314         return choke_match_flow(oskb, nskb);
 315 }
 316
 317 static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 318 {
 319         struct choke_sched_data *q = qdisc_priv(sch);
 320         struct red_parms *p = &q->parms;
 321         int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
 322
 323         if (q->filter_list) {
 324                 /* If using external classifiers, get result and record it. */
 325                 if (!choke_classify(skb, sch, &ret))
 326                         goto other_drop;        /* Packet was eaten by filter */
 327         }
 328
 329         /* Compute average queue usage (see RED) */
 330         p->qavg = red_calc_qavg(p, sch->q.qlen);
 331         if (red_is_idling(p))
 332                 red_end_of_idle_period(p);
 333
 334         /* Is queue small? */
 335         if (p->qavg <= p->qth_min)
 336                 p->qcount = -1;
 337         else {
 338                 unsigned int idx;
 339
 340                 /* Draw a packet at random from queue and compare flow */
 341                 if (choke_match_random(q, skb, &idx)) {
 342                         q->stats.matched++;
 343                         choke_drop_by_idx(sch, idx);
 344                         goto congestion_drop;
 345                 }
 346
 347                 /* Queue is large, always mark/drop */
 348                 if (p->qavg > p->qth_max) {
 349                         p->qcount = -1;
 350
 351                         sch->qstats.overlimits++;
 352                         if (use_harddrop(q) || !use_ecn(q) ||
 353                             !INET_ECN_set_ce(skb)) {
 354                                 q->stats.forced_drop++;
 355                                 goto congestion_drop;
 356                         }
 357
 358                         q->stats.forced_mark++;
 359                 } else if (++p->qcount) {
 360                         if (red_mark_probability(p, p->qavg)) {
 361                                 p->qcount = 0;
 362                                 p->qR = red_random(p);
 363
 364                                 sch->qstats.overlimits++;
 365                                 if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
 366                                         q->stats.prob_drop++;
 367                                         goto congestion_drop;
 368                                 }
 369
 370                                 q->stats.prob_mark++;
 371                         }
 372                 } else
 373                         p->qR = red_random(p);
 374         }
 375
 376         /* Admit new packet */
 377         if (sch->q.qlen < q->limit) {
 378                 q->tab[q->tail] = skb;
 379                 q->tail = (q->tail + 1) & q->tab_mask;
 380                 ++sch->q.qlen;
 381                 sch->qstats.backlog += qdisc_pkt_len(skb);
 382                 return NET_XMIT_SUCCESS;
 383         }
 384
 385         q->stats.pdrop++;
 386         sch->qstats.drops++;
 387         kfree_skb(skb);
 388         return NET_XMIT_DROP;
 389
 390  congestion_drop:
 391         qdisc_drop(skb, sch);
 392         return NET_XMIT_CN;
 393
 394  other_drop:
 395         if (ret & __NET_XMIT_BYPASS)
 396                 sch->qstats.drops++;
 397         kfree_skb(skb);
 398         return ret;
 399 }
 400
 401 static struct sk_buff *choke_dequeue(struct Qdisc *sch)
 402 {
 403         struct choke_sched_data *q = qdisc_priv(sch);
 404         struct sk_buff *skb;
 405
 406         if (q->head == q->tail) {
 407                 if (!red_is_idling(&q->parms))
 408                         red_start_of_idle_period(&q->parms);
 409                 return NULL;
 410         }
 411
 412         skb = q->tab[q->head];
 413         q->tab[q->head] = NULL;
 414         choke_zap_head_holes(q);
 415         --sch->q.qlen;
 416         sch->qstats.backlog -= qdisc_pkt_len(skb);
 417         qdisc_bstats_update(sch, skb);
 418
 419         return skb;
 420 }
 421
 422 static unsigned int choke_drop(struct Qdisc *sch)
 423 {
 424         struct choke_sched_data *q = qdisc_priv(sch);
 425         unsigned int len;
 426
 427         len = qdisc_queue_drop(sch);
 428         if (len > 0)
 429                 q->stats.other++;
 430         else {
 431                 if (!red_is_idling(&q->parms))
 432                         red_start_of_idle_period(&q->parms);
 433         }
 434
 435         return len;
 436 }
 437
 438 static void choke_reset(struct Qdisc *sch)
 439 {
 440         struct choke_sched_data *q = qdisc_priv(sch);
 441
 442         red_restart(&q->parms);
 443 }
 444
 445 static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
 446         [TCA_CHOKE_PARMS]       = { .len = sizeof(struct tc_red_qopt) },
 447         [TCA_CHOKE_STAB]        = { .len = RED_STAB_SIZE },
 448 };
 449
 450
 451 static void choke_free(void *addr)
 452 {
 453         if (addr) {
 454                 if (is_vmalloc_addr(addr))
 455                         vfree(addr);
 456                 else
 457                         kfree(addr);
 458         }
 459 }
 460
 461 static int choke_change(struct Qdisc *sch, struct nlattr *opt)
 462 {
 463         struct choke_sched_data *q = qdisc_priv(sch);
 464         struct nlattr *tb[TCA_CHOKE_MAX + 1];
 465         const struct tc_red_qopt *ctl;
 466         int err;
 467         struct sk_buff **old = NULL;
 468         unsigned int mask;
 469
 470         if (opt == NULL)
 471                 return -EINVAL;
 472
 473         err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
 474         if (err < 0)
 475                 return err;
 476
 477         if (tb[TCA_CHOKE_PARMS] == NULL ||
 478             tb[TCA_CHOKE_STAB] == NULL)
 479                 return -EINVAL;
 480
 481         ctl = nla_data(tb[TCA_CHOKE_PARMS]);
 482
 483         if (ctl->limit > CHOKE_MAX_QUEUE)
 484                 return -EINVAL;
 485
 486         mask = roundup_pow_of_two(ctl->limit + 1) - 1;
 487         if (mask != q->tab_mask) {
 488                 struct sk_buff **ntab;
 489
 490                 ntab = kcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
 491                 if (!ntab)
 492                         ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
 493                 if (!ntab)
 494                         return -ENOMEM;
 495
 496                 sch_tree_lock(sch);
 497                 old = q->tab;
 498                 if (old) {
 499                         unsigned int oqlen = sch->q.qlen, tail = 0;
 500
 501                         while (q->head != q->tail) {
 502                                 struct sk_buff *skb = q->tab[q->head];
 503
 504                                 q->head = (q->head + 1) & q->tab_mask;
 505                                 if (!skb)
 506                                         continue;
 507                                 if (tail < mask) {
 508                                         ntab[tail++] = skb;
 509                                         continue;
 510                                 }
 511                                 sch->qstats.backlog -= qdisc_pkt_len(skb);
 512                                 --sch->q.qlen;
 513                                 qdisc_drop(skb, sch);
 514                         }
 515                         qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
 516                         q->head = 0;
 517                         q->tail = tail;
 518                 }
 519
 520                 q->tab_mask = mask;
 521                 q->tab = ntab;
 522         } else
 523                 sch_tree_lock(sch);
 524
 525         q->flags = ctl->flags;
 526         q->limit = ctl->limit;
 527
 528         red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
 529                       ctl->Plog, ctl->Scell_log,
 530                       nla_data(tb[TCA_CHOKE_STAB]));
 531
 532         if (q->head == q->tail)
 533                 red_end_of_idle_period(&q->parms);
 534
 535         sch_tree_unlock(sch);
 536         choke_free(old);
 537         return 0;
 538 }
 539
 540 static int choke_init(struct Qdisc *sch, struct nlattr *opt)
 541 {
 542         return choke_change(sch, opt);
 543 }
 544
 545 static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
 546 {
 547         struct choke_sched_data *q = qdisc_priv(sch);
 548         struct nlattr *opts = NULL;
 549         struct tc_red_qopt opt = {
 550                 .limit          = q->limit,
 551                 .flags          = q->flags,
 552                 .qth_min        = q->parms.qth_min >> q->parms.Wlog,
 553                 .qth_max        = q->parms.qth_max >> q->parms.Wlog,
 554                 .Wlog           = q->parms.Wlog,
 555                 .Plog           = q->parms.Plog,
 556                 .Scell_log      = q->parms.Scell_log,
 557         };
 558
 559         opts = nla_nest_start(skb, TCA_OPTIONS);
 560         if (opts == NULL)
 561                 goto nla_put_failure;
 562
 563         NLA_PUT(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt);
 564         return nla_nest_end(skb, opts);
 565
 566 nla_put_failure:
 567         nla_nest_cancel(skb, opts);
 568         return -EMSGSIZE;
 569 }
 570
 571 static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 572 {
 573         struct choke_sched_data *q = qdisc_priv(sch);
 574         struct tc_choke_xstats st = {
 575                 .early  = q->stats.prob_drop + q->stats.forced_drop,
 576                 .marked = q->stats.prob_mark + q->stats.forced_mark,
 577                 .pdrop  = q->stats.pdrop,
 578                 .other  = q->stats.other,
 579                 .matched = q->stats.matched,
 580         };
 581
 582         return gnet_stats_copy_app(d, &st, sizeof(st));
 583 }
 584
 585 static void choke_destroy(struct Qdisc *sch)
 586 {
 587         struct choke_sched_data *q = qdisc_priv(sch);
 588
 589         tcf_destroy_chain(&q->filter_list);
 590         choke_free(q->tab);
 591 }
 592
 593 static struct Qdisc *choke_leaf(struct Qdisc *sch, unsigned long arg)
 594 {
 595         return NULL;
 596 }
 597
 598 static unsigned long choke_get(struct Qdisc *sch, u32 classid)
 599 {
 600         return 0;
 601 }
 602
 603 static void choke_put(struct Qdisc *q, unsigned long cl)
 604 {
 605 }
 606
 607 static unsigned long choke_bind(struct Qdisc *sch, unsigned long parent,
 608                                 u32 classid)
 609 {
 610         return 0;
 611 }
 612
 613 static struct tcf_proto **choke_find_tcf(struct Qdisc *sch, unsigned long cl)
 614 {
 615         struct choke_sched_data *q = qdisc_priv(sch);
 616
 617         if (cl)
 618                 return NULL;
 619         return &q->filter_list;
 620 }
 621
 622 static int choke_dump_class(struct Qdisc *sch, unsigned long cl,
 623                           struct sk_buff *skb, struct tcmsg *tcm)
 624 {
 625         tcm->tcm_handle |= TC_H_MIN(cl);
 626         return 0;
 627 }
 628
 629 static void choke_walk(struct Qdisc *sch, struct qdisc_walker *arg)
 630 {
 631         if (!arg->stop) {
 632                 if (arg->fn(sch, 1, arg) < 0) {
 633                         arg->stop = 1;
 634                         return;
 635                 }
 636                 arg->count++;
 637         }
 638 }
 639
 640 static const struct Qdisc_class_ops choke_class_ops = {
 641         .leaf           =       choke_leaf,
 642         .get            =       choke_get,
 643         .put            =       choke_put,
 644         .tcf_chain      =       choke_find_tcf,
 645         .bind_tcf       =       choke_bind,
 646         .unbind_tcf     =       choke_put,
 647         .dump           =       choke_dump_class,
 648         .walk           =       choke_walk,
 649 };
 650
 651 static struct sk_buff *choke_peek_head(struct Qdisc *sch)
 652 {
 653         struct choke_sched_data *q = qdisc_priv(sch);
 654
 655         return (q->head != q->tail) ? q->tab[q->head] : NULL;
 656 }
 657
 658 static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
 659         .id             =       "choke",
 660         .priv_size      =       sizeof(struct choke_sched_data),
 661
 662         .enqueue        =       choke_enqueue,
 663         .dequeue        =       choke_dequeue,
 664         .peek           =       choke_peek_head,
 665         .drop           =       choke_drop,
 666         .init           =       choke_init,
 667         .destroy        =       choke_destroy,
 668         .reset          =       choke_reset,
 669         .change         =       choke_change,
 670         .dump           =       choke_dump,
 671         .dump_stats     =       choke_dump_stats,
 672         .owner          =       THIS_MODULE,
 673 };
 674
 675 static int __init choke_module_init(void)
 676 {
 677         return register_qdisc(&choke_qdisc_ops);
 678 }
 679
 680 static void __exit choke_module_exit(void)
 681 {
 682         unregister_qdisc(&choke_qdisc_ops);
 683 }
 684
 685 module_init(choke_module_init)
 686 module_exit(choke_module_exit)
 687
 688 MODULE_LICENSE("GPL");