linux/net/sched/sch_choke.c
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   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 <net/flow_keys.h>
  23
  24/*
  25   CHOKe stateless AQM for fair bandwidth allocation
  26   =================================================
  27
  28   CHOKe (CHOose and Keep for responsive flows, CHOose and Kill for
  29   unresponsive flows) is a variant of RED that penalizes misbehaving flows but
  30   maintains no flow state. The difference from RED is an additional step
  31   during the enqueuing process. If average queue size is over the
  32   low threshold (qmin), a packet is chosen at random from the queue.
  33   If both the new and chosen packet are from the same flow, both
  34   are dropped. Unlike RED, CHOKe is not really a "classful" qdisc because it
  35   needs to access packets in queue randomly. It has a minimal class
  36   interface to allow overriding the builtin flow classifier with
  37   filters.
  38
  39   Source:
  40   R. Pan, B. Prabhakar, and K. Psounis, "CHOKe, A Stateless
  41   Active Queue Management Scheme for Approximating Fair Bandwidth Allocation",
  42   IEEE INFOCOM, 2000.
  43
  44   A. Tang, J. Wang, S. Low, "Understanding CHOKe: Throughput and Spatial
  45   Characteristics", IEEE/ACM Transactions on Networking, 2004
  46
  47 */
  48
  49/* Upper bound on size of sk_buff table (packets) */
  50#define CHOKE_MAX_QUEUE (128*1024 - 1)
  51
  52struct choke_sched_data {
  53/* Parameters */
  54        u32              limit;
  55        unsigned char    flags;
  56
  57        struct red_parms parms;
  58
  59/* Variables */
  60        struct red_vars  vars;
  61        struct tcf_proto *filter_list;
  62        struct {
  63                u32     prob_drop;      /* Early probability drops */
  64                u32     prob_mark;      /* Early probability marks */
  65                u32     forced_drop;    /* Forced drops, qavg > max_thresh */
  66                u32     forced_mark;    /* Forced marks, qavg > max_thresh */
  67                u32     pdrop;          /* Drops due to queue limits */
  68                u32     other;          /* Drops due to drop() calls */
  69                u32     matched;        /* Drops to flow match */
  70        } stats;
  71
  72        unsigned int     head;
  73        unsigned int     tail;
  74
  75        unsigned int     tab_mask; /* size - 1 */
  76
  77        struct sk_buff **tab;
  78};
  79
  80/* deliver a random number between 0 and N - 1 */
  81static u32 random_N(unsigned int N)
  82{
  83        return reciprocal_divide(random32(), N);
  84}
  85
  86/* number of elements in queue including holes */
  87static unsigned int choke_len(const struct choke_sched_data *q)
  88{
  89        return (q->tail - q->head) & q->tab_mask;
  90}
  91
  92/* Is ECN parameter configured */
  93static int use_ecn(const struct choke_sched_data *q)
  94{
  95        return q->flags & TC_RED_ECN;
  96}
  97
  98/* Should packets over max just be dropped (versus marked) */
  99static int use_harddrop(const struct choke_sched_data *q)
 100{
 101        return q->flags & TC_RED_HARDDROP;
 102}
 103
 104/* Move head pointer forward to skip over holes */
 105static void choke_zap_head_holes(struct choke_sched_data *q)
 106{
 107        do {
 108                q->head = (q->head + 1) & q->tab_mask;
 109                if (q->head == q->tail)
 110                        break;
 111        } while (q->tab[q->head] == NULL);
 112}
 113
 114/* Move tail pointer backwards to reuse holes */
 115static void choke_zap_tail_holes(struct choke_sched_data *q)
 116{
 117        do {
 118                q->tail = (q->tail - 1) & q->tab_mask;
 119                if (q->head == q->tail)
 120                        break;
 121        } while (q->tab[q->tail] == NULL);
 122}
 123
 124/* Drop packet from queue array by creating a "hole" */
 125static void choke_drop_by_idx(struct Qdisc *sch, unsigned int idx)
 126{
 127        struct choke_sched_data *q = qdisc_priv(sch);
 128        struct sk_buff *skb = q->tab[idx];
 129
 130        q->tab[idx] = NULL;
 131
 132        if (idx == q->head)
 133                choke_zap_head_holes(q);
 134        if (idx == q->tail)
 135                choke_zap_tail_holes(q);
 136
 137        sch->qstats.backlog -= qdisc_pkt_len(skb);
 138        qdisc_drop(skb, sch);
 139        qdisc_tree_decrease_qlen(sch, 1);
 140        --sch->q.qlen;
 141}
 142
 143struct choke_skb_cb {
 144        u16                     classid;
 145        u8                      keys_valid;
 146        struct flow_keys        keys;
 147};
 148
 149static inline struct choke_skb_cb *choke_skb_cb(const struct sk_buff *skb)
 150{
 151        qdisc_cb_private_validate(skb, sizeof(struct choke_skb_cb));
 152        return (struct choke_skb_cb *)qdisc_skb_cb(skb)->data;
 153}
 154
 155static inline void choke_set_classid(struct sk_buff *skb, u16 classid)
 156{
 157        choke_skb_cb(skb)->classid = classid;
 158}
 159
 160static u16 choke_get_classid(const struct sk_buff *skb)
 161{
 162        return choke_skb_cb(skb)->classid;
 163}
 164
 165/*
 166 * Compare flow of two packets
 167 *  Returns true only if source and destination address and port match.
 168 *          false for special cases
 169 */
 170static bool choke_match_flow(struct sk_buff *skb1,
 171                             struct sk_buff *skb2)
 172{
 173        if (skb1->protocol != skb2->protocol)
 174                return false;
 175
 176        if (!choke_skb_cb(skb1)->keys_valid) {
 177                choke_skb_cb(skb1)->keys_valid = 1;
 178                skb_flow_dissect(skb1, &choke_skb_cb(skb1)->keys);
 179        }
 180
 181        if (!choke_skb_cb(skb2)->keys_valid) {
 182                choke_skb_cb(skb2)->keys_valid = 1;
 183                skb_flow_dissect(skb2, &choke_skb_cb(skb2)->keys);
 184        }
 185
 186        return !memcmp(&choke_skb_cb(skb1)->keys,
 187                       &choke_skb_cb(skb2)->keys,
 188                       sizeof(struct flow_keys));
 189}
 190
 191/*
 192 * Classify flow using either:
 193 *  1. pre-existing classification result in skb
 194 *  2. fast internal classification
 195 *  3. use TC filter based classification
 196 */
 197static bool choke_classify(struct sk_buff *skb,
 198                           struct Qdisc *sch, int *qerr)
 199
 200{
 201        struct choke_sched_data *q = qdisc_priv(sch);
 202        struct tcf_result res;
 203        int result;
 204
 205        result = tc_classify(skb, q->filter_list, &res);
 206        if (result >= 0) {
 207#ifdef CONFIG_NET_CLS_ACT
 208                switch (result) {
 209                case TC_ACT_STOLEN:
 210                case TC_ACT_QUEUED:
 211                        *qerr = NET_XMIT_SUCCESS | __NET_XMIT_STOLEN;
 212                case TC_ACT_SHOT:
 213                        return false;
 214                }
 215#endif
 216                choke_set_classid(skb, TC_H_MIN(res.classid));
 217                return true;
 218        }
 219
 220        return false;
 221}
 222
 223/*
 224 * Select a packet at random from queue
 225 * HACK: since queue can have holes from previous deletion; retry several
 226 *   times to find a random skb but then just give up and return the head
 227 * Will return NULL if queue is empty (q->head == q->tail)
 228 */
 229static struct sk_buff *choke_peek_random(const struct choke_sched_data *q,
 230                                         unsigned int *pidx)
 231{
 232        struct sk_buff *skb;
 233        int retrys = 3;
 234
 235        do {
 236                *pidx = (q->head + random_N(choke_len(q))) & q->tab_mask;
 237                skb = q->tab[*pidx];
 238                if (skb)
 239                        return skb;
 240        } while (--retrys > 0);
 241
 242        return q->tab[*pidx = q->head];
 243}
 244
 245/*
 246 * Compare new packet with random packet in queue
 247 * returns true if matched and sets *pidx
 248 */
 249static bool choke_match_random(const struct choke_sched_data *q,
 250                               struct sk_buff *nskb,
 251                               unsigned int *pidx)
 252{
 253        struct sk_buff *oskb;
 254
 255        if (q->head == q->tail)
 256                return false;
 257
 258        oskb = choke_peek_random(q, pidx);
 259        if (q->filter_list)
 260                return choke_get_classid(nskb) == choke_get_classid(oskb);
 261
 262        return choke_match_flow(oskb, nskb);
 263}
 264
 265static int choke_enqueue(struct sk_buff *skb, struct Qdisc *sch)
 266{
 267        struct choke_sched_data *q = qdisc_priv(sch);
 268        const struct red_parms *p = &q->parms;
 269        int ret = NET_XMIT_SUCCESS | __NET_XMIT_BYPASS;
 270
 271        if (q->filter_list) {
 272                /* If using external classifiers, get result and record it. */
 273                if (!choke_classify(skb, sch, &ret))
 274                        goto other_drop;        /* Packet was eaten by filter */
 275        }
 276
 277        choke_skb_cb(skb)->keys_valid = 0;
 278        /* Compute average queue usage (see RED) */
 279        q->vars.qavg = red_calc_qavg(p, &q->vars, sch->q.qlen);
 280        if (red_is_idling(&q->vars))
 281                red_end_of_idle_period(&q->vars);
 282
 283        /* Is queue small? */
 284        if (q->vars.qavg <= p->qth_min)
 285                q->vars.qcount = -1;
 286        else {
 287                unsigned int idx;
 288
 289                /* Draw a packet at random from queue and compare flow */
 290                if (choke_match_random(q, skb, &idx)) {
 291                        q->stats.matched++;
 292                        choke_drop_by_idx(sch, idx);
 293                        goto congestion_drop;
 294                }
 295
 296                /* Queue is large, always mark/drop */
 297                if (q->vars.qavg > p->qth_max) {
 298                        q->vars.qcount = -1;
 299
 300                        sch->qstats.overlimits++;
 301                        if (use_harddrop(q) || !use_ecn(q) ||
 302                            !INET_ECN_set_ce(skb)) {
 303                                q->stats.forced_drop++;
 304                                goto congestion_drop;
 305                        }
 306
 307                        q->stats.forced_mark++;
 308                } else if (++q->vars.qcount) {
 309                        if (red_mark_probability(p, &q->vars, q->vars.qavg)) {
 310                                q->vars.qcount = 0;
 311                                q->vars.qR = red_random(p);
 312
 313                                sch->qstats.overlimits++;
 314                                if (!use_ecn(q) || !INET_ECN_set_ce(skb)) {
 315                                        q->stats.prob_drop++;
 316                                        goto congestion_drop;
 317                                }
 318
 319                                q->stats.prob_mark++;
 320                        }
 321                } else
 322                        q->vars.qR = red_random(p);
 323        }
 324
 325        /* Admit new packet */
 326        if (sch->q.qlen < q->limit) {
 327                q->tab[q->tail] = skb;
 328                q->tail = (q->tail + 1) & q->tab_mask;
 329                ++sch->q.qlen;
 330                sch->qstats.backlog += qdisc_pkt_len(skb);
 331                return NET_XMIT_SUCCESS;
 332        }
 333
 334        q->stats.pdrop++;
 335        return qdisc_drop(skb, sch);
 336
 337congestion_drop:
 338        qdisc_drop(skb, sch);
 339        return NET_XMIT_CN;
 340
 341other_drop:
 342        if (ret & __NET_XMIT_BYPASS)
 343                sch->qstats.drops++;
 344        kfree_skb(skb);
 345        return ret;
 346}
 347
 348static struct sk_buff *choke_dequeue(struct Qdisc *sch)
 349{
 350        struct choke_sched_data *q = qdisc_priv(sch);
 351        struct sk_buff *skb;
 352
 353        if (q->head == q->tail) {
 354                if (!red_is_idling(&q->vars))
 355                        red_start_of_idle_period(&q->vars);
 356                return NULL;
 357        }
 358
 359        skb = q->tab[q->head];
 360        q->tab[q->head] = NULL;
 361        choke_zap_head_holes(q);
 362        --sch->q.qlen;
 363        sch->qstats.backlog -= qdisc_pkt_len(skb);
 364        qdisc_bstats_update(sch, skb);
 365
 366        return skb;
 367}
 368
 369static unsigned int choke_drop(struct Qdisc *sch)
 370{
 371        struct choke_sched_data *q = qdisc_priv(sch);
 372        unsigned int len;
 373
 374        len = qdisc_queue_drop(sch);
 375        if (len > 0)
 376                q->stats.other++;
 377        else {
 378                if (!red_is_idling(&q->vars))
 379                        red_start_of_idle_period(&q->vars);
 380        }
 381
 382        return len;
 383}
 384
 385static void choke_reset(struct Qdisc *sch)
 386{
 387        struct choke_sched_data *q = qdisc_priv(sch);
 388
 389        red_restart(&q->vars);
 390}
 391
 392static const struct nla_policy choke_policy[TCA_CHOKE_MAX + 1] = {
 393        [TCA_CHOKE_PARMS]       = { .len = sizeof(struct tc_red_qopt) },
 394        [TCA_CHOKE_STAB]        = { .len = RED_STAB_SIZE },
 395        [TCA_CHOKE_MAX_P]       = { .type = NLA_U32 },
 396};
 397
 398
 399static void choke_free(void *addr)
 400{
 401        if (addr) {
 402                if (is_vmalloc_addr(addr))
 403                        vfree(addr);
 404                else
 405                        kfree(addr);
 406        }
 407}
 408
 409static int choke_change(struct Qdisc *sch, struct nlattr *opt)
 410{
 411        struct choke_sched_data *q = qdisc_priv(sch);
 412        struct nlattr *tb[TCA_CHOKE_MAX + 1];
 413        const struct tc_red_qopt *ctl;
 414        int err;
 415        struct sk_buff **old = NULL;
 416        unsigned int mask;
 417        u32 max_P;
 418
 419        if (opt == NULL)
 420                return -EINVAL;
 421
 422        err = nla_parse_nested(tb, TCA_CHOKE_MAX, opt, choke_policy);
 423        if (err < 0)
 424                return err;
 425
 426        if (tb[TCA_CHOKE_PARMS] == NULL ||
 427            tb[TCA_CHOKE_STAB] == NULL)
 428                return -EINVAL;
 429
 430        max_P = tb[TCA_CHOKE_MAX_P] ? nla_get_u32(tb[TCA_CHOKE_MAX_P]) : 0;
 431
 432        ctl = nla_data(tb[TCA_CHOKE_PARMS]);
 433
 434        if (ctl->limit > CHOKE_MAX_QUEUE)
 435                return -EINVAL;
 436
 437        mask = roundup_pow_of_two(ctl->limit + 1) - 1;
 438        if (mask != q->tab_mask) {
 439                struct sk_buff **ntab;
 440
 441                ntab = kcalloc(mask + 1, sizeof(struct sk_buff *), GFP_KERNEL);
 442                if (!ntab)
 443                        ntab = vzalloc((mask + 1) * sizeof(struct sk_buff *));
 444                if (!ntab)
 445                        return -ENOMEM;
 446
 447                sch_tree_lock(sch);
 448                old = q->tab;
 449                if (old) {
 450                        unsigned int oqlen = sch->q.qlen, tail = 0;
 451
 452                        while (q->head != q->tail) {
 453                                struct sk_buff *skb = q->tab[q->head];
 454
 455                                q->head = (q->head + 1) & q->tab_mask;
 456                                if (!skb)
 457                                        continue;
 458                                if (tail < mask) {
 459                                        ntab[tail++] = skb;
 460                                        continue;
 461                                }
 462                                sch->qstats.backlog -= qdisc_pkt_len(skb);
 463                                --sch->q.qlen;
 464                                qdisc_drop(skb, sch);
 465                        }
 466                        qdisc_tree_decrease_qlen(sch, oqlen - sch->q.qlen);
 467                        q->head = 0;
 468                        q->tail = tail;
 469                }
 470
 471                q->tab_mask = mask;
 472                q->tab = ntab;
 473        } else
 474                sch_tree_lock(sch);
 475
 476        q->flags = ctl->flags;
 477        q->limit = ctl->limit;
 478
 479        red_set_parms(&q->parms, ctl->qth_min, ctl->qth_max, ctl->Wlog,
 480                      ctl->Plog, ctl->Scell_log,
 481                      nla_data(tb[TCA_CHOKE_STAB]),
 482                      max_P);
 483        red_set_vars(&q->vars);
 484
 485        if (q->head == q->tail)
 486                red_end_of_idle_period(&q->vars);
 487
 488        sch_tree_unlock(sch);
 489        choke_free(old);
 490        return 0;
 491}
 492
 493static int choke_init(struct Qdisc *sch, struct nlattr *opt)
 494{
 495        return choke_change(sch, opt);
 496}
 497
 498static int choke_dump(struct Qdisc *sch, struct sk_buff *skb)
 499{
 500        struct choke_sched_data *q = qdisc_priv(sch);
 501        struct nlattr *opts = NULL;
 502        struct tc_red_qopt opt = {
 503                .limit          = q->limit,
 504                .flags          = q->flags,
 505                .qth_min        = q->parms.qth_min >> q->parms.Wlog,
 506                .qth_max        = q->parms.qth_max >> q->parms.Wlog,
 507                .Wlog           = q->parms.Wlog,
 508                .Plog           = q->parms.Plog,
 509                .Scell_log      = q->parms.Scell_log,
 510        };
 511
 512        opts = nla_nest_start(skb, TCA_OPTIONS);
 513        if (opts == NULL)
 514                goto nla_put_failure;
 515
 516        if (nla_put(skb, TCA_CHOKE_PARMS, sizeof(opt), &opt) ||
 517            nla_put_u32(skb, TCA_CHOKE_MAX_P, q->parms.max_P))
 518                goto nla_put_failure;
 519        return nla_nest_end(skb, opts);
 520
 521nla_put_failure:
 522        nla_nest_cancel(skb, opts);
 523        return -EMSGSIZE;
 524}
 525
 526static int choke_dump_stats(struct Qdisc *sch, struct gnet_dump *d)
 527{
 528        struct choke_sched_data *q = qdisc_priv(sch);
 529        struct tc_choke_xstats st = {
 530                .early  = q->stats.prob_drop + q->stats.forced_drop,
 531                .marked = q->stats.prob_mark + q->stats.forced_mark,
 532                .pdrop  = q->stats.pdrop,
 533                .other  = q->stats.other,
 534                .matched = q->stats.matched,
 535        };
 536
 537        return gnet_stats_copy_app(d, &st, sizeof(st));
 538}
 539
 540static void choke_destroy(struct Qdisc *sch)
 541{
 542        struct choke_sched_data *q = qdisc_priv(sch);
 543
 544        tcf_destroy_chain(&q->filter_list);
 545        choke_free(q->tab);
 546}
 547
 548static struct Qdisc *choke_leaf(struct Qdisc *sch, unsigned long arg)
 549{
 550        return NULL;
 551}
 552
 553static unsigned long choke_get(struct Qdisc *sch, u32 classid)
 554{
 555        return 0;
 556}
 557
 558static void choke_put(struct Qdisc *q, unsigned long cl)
 559{
 560}
 561
 562static unsigned long choke_bind(struct Qdisc *sch, unsigned long parent,
 563                                u32 classid)
 564{
 565        return 0;
 566}
 567
 568static struct tcf_proto **choke_find_tcf(struct Qdisc *sch, unsigned long cl)
 569{
 570        struct choke_sched_data *q = qdisc_priv(sch);
 571
 572        if (cl)
 573                return NULL;
 574        return &q->filter_list;
 575}
 576
 577static int choke_dump_class(struct Qdisc *sch, unsigned long cl,
 578                          struct sk_buff *skb, struct tcmsg *tcm)
 579{
 580        tcm->tcm_handle |= TC_H_MIN(cl);
 581        return 0;
 582}
 583
 584static void choke_walk(struct Qdisc *sch, struct qdisc_walker *arg)
 585{
 586        if (!arg->stop) {
 587                if (arg->fn(sch, 1, arg) < 0) {
 588                        arg->stop = 1;
 589                        return;
 590                }
 591                arg->count++;
 592        }
 593}
 594
 595static const struct Qdisc_class_ops choke_class_ops = {
 596        .leaf           =       choke_leaf,
 597        .get            =       choke_get,
 598        .put            =       choke_put,
 599        .tcf_chain      =       choke_find_tcf,
 600        .bind_tcf       =       choke_bind,
 601        .unbind_tcf     =       choke_put,
 602        .dump           =       choke_dump_class,
 603        .walk           =       choke_walk,
 604};
 605
 606static struct sk_buff *choke_peek_head(struct Qdisc *sch)
 607{
 608        struct choke_sched_data *q = qdisc_priv(sch);
 609
 610        return (q->head != q->tail) ? q->tab[q->head] : NULL;
 611}
 612
 613static struct Qdisc_ops choke_qdisc_ops __read_mostly = {
 614        .id             =       "choke",
 615        .priv_size      =       sizeof(struct choke_sched_data),
 616
 617        .enqueue        =       choke_enqueue,
 618        .dequeue        =       choke_dequeue,
 619        .peek           =       choke_peek_head,
 620        .drop           =       choke_drop,
 621        .init           =       choke_init,
 622        .destroy        =       choke_destroy,
 623        .reset          =       choke_reset,
 624        .change         =       choke_change,
 625        .dump           =       choke_dump,
 626        .dump_stats     =       choke_dump_stats,
 627        .owner          =       THIS_MODULE,
 628};
 629
 630static int __init choke_module_init(void)
 631{
 632        return register_qdisc(&choke_qdisc_ops);
 633}
 634
 635static void __exit choke_module_exit(void)
 636{
 637        unregister_qdisc(&choke_qdisc_ops);
 638}
 639
 640module_init(choke_module_init)
 641module_exit(choke_module_exit)
 642
 643MODULE_LICENSE("GPL");
 644
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