linux/net/ipv4/tcp_cong.c
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   1/*
   2 * Plugable TCP congestion control support and newReno
   3 * congestion control.
   4 * Based on ideas from I/O scheduler suport and Web100.
   5 *
   6 * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
   7 */
   8
   9#include <linux/module.h>
  10#include <linux/mm.h>
  11#include <linux/types.h>
  12#include <linux/list.h>
  13#include <net/tcp.h>
  14
  15int sysctl_tcp_max_ssthresh = 0;
  16
  17static DEFINE_SPINLOCK(tcp_cong_list_lock);
  18static LIST_HEAD(tcp_cong_list);
  19
  20/* Simple linear search, don't expect many entries! */
  21static struct tcp_congestion_ops *tcp_ca_find(const char *name)
  22{
  23        struct tcp_congestion_ops *e;
  24
  25        list_for_each_entry_rcu(e, &tcp_cong_list, list) {
  26                if (strcmp(e->name, name) == 0)
  27                        return e;
  28        }
  29
  30        return NULL;
  31}
  32
  33/*
  34 * Attach new congestion control algorithm to the list
  35 * of available options.
  36 */
  37int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
  38{
  39        int ret = 0;
  40
  41        /* all algorithms must implement ssthresh and cong_avoid ops */
  42        if (!ca->ssthresh || !ca->cong_avoid) {
  43                printk(KERN_ERR "TCP %s does not implement required ops\n",
  44                       ca->name);
  45                return -EINVAL;
  46        }
  47
  48        spin_lock(&tcp_cong_list_lock);
  49        if (tcp_ca_find(ca->name)) {
  50                printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
  51                ret = -EEXIST;
  52        } else {
  53                list_add_tail_rcu(&ca->list, &tcp_cong_list);
  54                printk(KERN_INFO "TCP %s registered\n", ca->name);
  55        }
  56        spin_unlock(&tcp_cong_list_lock);
  57
  58        return ret;
  59}
  60EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
  61
  62/*
  63 * Remove congestion control algorithm, called from
  64 * the module's remove function.  Module ref counts are used
  65 * to ensure that this can't be done till all sockets using
  66 * that method are closed.
  67 */
  68void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
  69{
  70        spin_lock(&tcp_cong_list_lock);
  71        list_del_rcu(&ca->list);
  72        spin_unlock(&tcp_cong_list_lock);
  73}
  74EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
  75
  76/* Assign choice of congestion control. */
  77void tcp_init_congestion_control(struct sock *sk)
  78{
  79        struct inet_connection_sock *icsk = inet_csk(sk);
  80        struct tcp_congestion_ops *ca;
  81
  82        /* if no choice made yet assign the current value set as default */
  83        if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
  84                rcu_read_lock();
  85                list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
  86                        if (try_module_get(ca->owner)) {
  87                                icsk->icsk_ca_ops = ca;
  88                                break;
  89                        }
  90
  91                        /* fallback to next available */
  92                }
  93                rcu_read_unlock();
  94        }
  95
  96        if (icsk->icsk_ca_ops->init)
  97                icsk->icsk_ca_ops->init(sk);
  98}
  99
 100/* Manage refcounts on socket close. */
 101void tcp_cleanup_congestion_control(struct sock *sk)
 102{
 103        struct inet_connection_sock *icsk = inet_csk(sk);
 104
 105        if (icsk->icsk_ca_ops->release)
 106                icsk->icsk_ca_ops->release(sk);
 107        module_put(icsk->icsk_ca_ops->owner);
 108}
 109
 110/* Used by sysctl to change default congestion control */
 111int tcp_set_default_congestion_control(const char *name)
 112{
 113        struct tcp_congestion_ops *ca;
 114        int ret = -ENOENT;
 115
 116        spin_lock(&tcp_cong_list_lock);
 117        ca = tcp_ca_find(name);
 118#ifdef CONFIG_MODULES
 119        if (!ca && capable(CAP_SYS_MODULE)) {
 120                spin_unlock(&tcp_cong_list_lock);
 121
 122                request_module("tcp_%s", name);
 123                spin_lock(&tcp_cong_list_lock);
 124                ca = tcp_ca_find(name);
 125        }
 126#endif
 127
 128        if (ca) {
 129                ca->flags |= TCP_CONG_NON_RESTRICTED;   /* default is always allowed */
 130                list_move(&ca->list, &tcp_cong_list);
 131                ret = 0;
 132        }
 133        spin_unlock(&tcp_cong_list_lock);
 134
 135        return ret;
 136}
 137
 138/* Set default value from kernel configuration at bootup */
 139static int __init tcp_congestion_default(void)
 140{
 141        return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 142}
 143late_initcall(tcp_congestion_default);
 144
 145
 146/* Build string with list of available congestion control values */
 147void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 148{
 149        struct tcp_congestion_ops *ca;
 150        size_t offs = 0;
 151
 152        rcu_read_lock();
 153        list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 154                offs += snprintf(buf + offs, maxlen - offs,
 155                                 "%s%s",
 156                                 offs == 0 ? "" : " ", ca->name);
 157
 158        }
 159        rcu_read_unlock();
 160}
 161
 162/* Get current default congestion control */
 163void tcp_get_default_congestion_control(char *name)
 164{
 165        struct tcp_congestion_ops *ca;
 166        /* We will always have reno... */
 167        BUG_ON(list_empty(&tcp_cong_list));
 168
 169        rcu_read_lock();
 170        ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 171        strncpy(name, ca->name, TCP_CA_NAME_MAX);
 172        rcu_read_unlock();
 173}
 174
 175/* Built list of non-restricted congestion control values */
 176void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 177{
 178        struct tcp_congestion_ops *ca;
 179        size_t offs = 0;
 180
 181        *buf = '\0';
 182        rcu_read_lock();
 183        list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 184                if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 185                        continue;
 186                offs += snprintf(buf + offs, maxlen - offs,
 187                                 "%s%s",
 188                                 offs == 0 ? "" : " ", ca->name);
 189
 190        }
 191        rcu_read_unlock();
 192}
 193
 194/* Change list of non-restricted congestion control */
 195int tcp_set_allowed_congestion_control(char *val)
 196{
 197        struct tcp_congestion_ops *ca;
 198        char *clone, *name;
 199        int ret = 0;
 200
 201        clone = kstrdup(val, GFP_USER);
 202        if (!clone)
 203                return -ENOMEM;
 204
 205        spin_lock(&tcp_cong_list_lock);
 206        /* pass 1 check for bad entries */
 207        while ((name = strsep(&clone, " ")) && *name) {
 208                ca = tcp_ca_find(name);
 209                if (!ca) {
 210                        ret = -ENOENT;
 211                        goto out;
 212                }
 213        }
 214
 215        /* pass 2 clear old values */
 216        list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 217                ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 218
 219        /* pass 3 mark as allowed */
 220        while ((name = strsep(&val, " ")) && *name) {
 221                ca = tcp_ca_find(name);
 222                WARN_ON(!ca);
 223                if (ca)
 224                        ca->flags |= TCP_CONG_NON_RESTRICTED;
 225        }
 226out:
 227        spin_unlock(&tcp_cong_list_lock);
 228
 229        return ret;
 230}
 231
 232
 233/* Change congestion control for socket */
 234int tcp_set_congestion_control(struct sock *sk, const char *name)
 235{
 236        struct inet_connection_sock *icsk = inet_csk(sk);
 237        struct tcp_congestion_ops *ca;
 238        int err = 0;
 239
 240        rcu_read_lock();
 241        ca = tcp_ca_find(name);
 242
 243        /* no change asking for existing value */
 244        if (ca == icsk->icsk_ca_ops)
 245                goto out;
 246
 247#ifdef CONFIG_MODULES
 248        /* not found attempt to autoload module */
 249        if (!ca && capable(CAP_SYS_MODULE)) {
 250                rcu_read_unlock();
 251                request_module("tcp_%s", name);
 252                rcu_read_lock();
 253                ca = tcp_ca_find(name);
 254        }
 255#endif
 256        if (!ca)
 257                err = -ENOENT;
 258
 259        else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) || capable(CAP_NET_ADMIN)))
 260                err = -EPERM;
 261
 262        else if (!try_module_get(ca->owner))
 263                err = -EBUSY;
 264
 265        else {
 266                tcp_cleanup_congestion_control(sk);
 267                icsk->icsk_ca_ops = ca;
 268
 269                if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
 270                        icsk->icsk_ca_ops->init(sk);
 271        }
 272 out:
 273        rcu_read_unlock();
 274        return err;
 275}
 276
 277/* RFC2861 Check whether we are limited by application or congestion window
 278 * This is the inverse of cwnd check in tcp_tso_should_defer
 279 */
 280int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
 281{
 282        const struct tcp_sock *tp = tcp_sk(sk);
 283        u32 left;
 284
 285        if (in_flight >= tp->snd_cwnd)
 286                return 1;
 287
 288        left = tp->snd_cwnd - in_flight;
 289        if (sk_can_gso(sk) &&
 290            left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
 291            left * tp->mss_cache < sk->sk_gso_max_size)
 292                return 1;
 293        return left <= tcp_max_burst(tp);
 294}
 295EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
 296
 297/*
 298 * Slow start is used when congestion window is less than slow start
 299 * threshold. This version implements the basic RFC2581 version
 300 * and optionally supports:
 301 *      RFC3742 Limited Slow Start        - growth limited to max_ssthresh
 302 *      RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
 303 */
 304void tcp_slow_start(struct tcp_sock *tp)
 305{
 306        int cnt; /* increase in packets */
 307
 308        /* RFC3465: ABC Slow start
 309         * Increase only after a full MSS of bytes is acked
 310         *
 311         * TCP sender SHOULD increase cwnd by the number of
 312         * previously unacknowledged bytes ACKed by each incoming
 313         * acknowledgment, provided the increase is not more than L
 314         */
 315        if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)
 316                return;
 317
 318        if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
 319                cnt = sysctl_tcp_max_ssthresh >> 1;     /* limited slow start */
 320        else
 321                cnt = tp->snd_cwnd;                     /* exponential increase */
 322
 323        /* RFC3465: ABC
 324         * We MAY increase by 2 if discovered delayed ack
 325         */
 326        if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
 327                cnt <<= 1;
 328        tp->bytes_acked = 0;
 329
 330        tp->snd_cwnd_cnt += cnt;
 331        while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 332                tp->snd_cwnd_cnt -= tp->snd_cwnd;
 333                if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 334                        tp->snd_cwnd++;
 335        }
 336}
 337EXPORT_SYMBOL_GPL(tcp_slow_start);
 338
 339/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
 340void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
 341{
 342        if (tp->snd_cwnd_cnt >= w) {
 343                if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 344                        tp->snd_cwnd++;
 345                tp->snd_cwnd_cnt = 0;
 346        } else {
 347                tp->snd_cwnd_cnt++;
 348        }
 349}
 350EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 351
 352/*
 353 * TCP Reno congestion control
 354 * This is special case used for fallback as well.
 355 */
 356/* This is Jacobson's slow start and congestion avoidance.
 357 * SIGCOMM '88, p. 328.
 358 */
 359void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 360{
 361        struct tcp_sock *tp = tcp_sk(sk);
 362
 363        if (!tcp_is_cwnd_limited(sk, in_flight))
 364                return;
 365
 366        /* In "safe" area, increase. */
 367        if (tp->snd_cwnd <= tp->snd_ssthresh)
 368                tcp_slow_start(tp);
 369
 370        /* In dangerous area, increase slowly. */
 371        else if (sysctl_tcp_abc) {
 372                /* RFC3465: Appropriate Byte Count
 373                 * increase once for each full cwnd acked
 374                 */
 375                if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
 376                        tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
 377                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 378                                tp->snd_cwnd++;
 379                }
 380        } else {
 381                tcp_cong_avoid_ai(tp, tp->snd_cwnd);
 382        }
 383}
 384EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 385
 386/* Slow start threshold is half the congestion window (min 2) */
 387u32 tcp_reno_ssthresh(struct sock *sk)
 388{
 389        const struct tcp_sock *tp = tcp_sk(sk);
 390        return max(tp->snd_cwnd >> 1U, 2U);
 391}
 392EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 393
 394/* Lower bound on congestion window with halving. */
 395u32 tcp_reno_min_cwnd(const struct sock *sk)
 396{
 397        const struct tcp_sock *tp = tcp_sk(sk);
 398        return tp->snd_ssthresh/2;
 399}
 400EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
 401
 402struct tcp_congestion_ops tcp_reno = {
 403        .flags          = TCP_CONG_NON_RESTRICTED,
 404        .name           = "reno",
 405        .owner          = THIS_MODULE,
 406        .ssthresh       = tcp_reno_ssthresh,
 407        .cong_avoid     = tcp_reno_cong_avoid,
 408        .min_cwnd       = tcp_reno_min_cwnd,
 409};
 410
 411/* Initial congestion control used (until SYN)
 412 * really reno under another name so we can tell difference
 413 * during tcp_set_default_congestion_control
 414 */
 415struct tcp_congestion_ops tcp_init_congestion_ops  = {
 416        .name           = "",
 417        .owner          = THIS_MODULE,
 418        .ssthresh       = tcp_reno_ssthresh,
 419        .cong_avoid     = tcp_reno_cong_avoid,
 420        .min_cwnd       = tcp_reno_min_cwnd,
 421};
 422EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
 423