net/ipv4/tcp_cong.c

   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
  15 int sysctl_tcp_max_ssthresh = 0;
  16
  17 static DEFINE_SPINLOCK(tcp_cong_list_lock);
  18 static LIST_HEAD(tcp_cong_list);
  19
  20 /* Simple linear search, don't expect many entries! */
  21 static 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  */
  37 int 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 }
  60 EXPORT_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  */
  68 void 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 }
  74 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
  75
  76 /* Assign choice of congestion control. */
  77 void 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. */
 101 void 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 */
 111 int 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 */
 139 static int __init tcp_congestion_default(void)
 140 {
 141         return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 142 }
 143 late_initcall(tcp_congestion_default);
 144
 145
 146 /* Build string with list of available congestion control values */
 147 void 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 */
 163 void 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 */
 176 void 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 */
 195 int 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         }
 226 out:
 227         spin_unlock(&tcp_cong_list_lock);
 228
 229         return ret;
 230 }
 231
 232
 233 /* Change congestion control for socket */
 234 int 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  */
 280 int 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 }
 295 EXPORT_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  */
 304 void 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 }
 337 EXPORT_SYMBOL_GPL(tcp_slow_start);
 338
 339 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
 340 void 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 }
 350 EXPORT_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  */
 359 void 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 }
 384 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 385
 386 /* Slow start threshold is half the congestion window (min 2) */
 387 u32 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 }
 392 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 393
 394 /* Lower bound on congestion window with halving. */
 395 u32 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 }
 400 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
 401
 402 struct 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  */
 415 struct 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 };
 422 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);