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