net/ipv4/tcp_cong.c

   1 /*
   2  * Pluggable TCP congestion control support and newReno
   3  * congestion control.
   4  * Based on ideas from I/O scheduler support and Web100.
   5  *
   6  * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
   7  */
   8
   9 #define pr_fmt(fmt) "TCP: " fmt
  10
  11 #include <linux/module.h>
  12 #include <linux/mm.h>
  13 #include <linux/types.h>
  14 #include <linux/list.h>
  15 #include <linux/gfp.h>
  16 #include <net/tcp.h>
  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                 pr_err("%s does not implement required ops\n", ca->name);
  45                 return -EINVAL;
  46         }
  47
  48         spin_lock(&tcp_cong_list_lock);
  49         if (tcp_ca_find(ca->name)) {
  50                 pr_notice("%s already registered\n", ca->name);
  51                 ret = -EEXIST;
  52         } else {
  53                 list_add_tail_rcu(&ca->list, &tcp_cong_list);
  54                 pr_info("%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_assign_congestion_control(struct sock *sk)
  78 {
  79         struct inet_connection_sock *icsk = inet_csk(sk);
  80         struct tcp_congestion_ops *ca;
  81
  82         rcu_read_lock();
  83         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
  84                 if (likely(try_module_get(ca->owner))) {
  85                         icsk->icsk_ca_ops = ca;
  86                         goto out;
  87                 }
  88                 /* Fallback to next available. The last really
  89                  * guaranteed fallback is Reno from this list.
  90                  */
  91         }
  92 out:
  93         rcu_read_unlock();
  94
  95         /* Clear out private data before diag gets it and
  96          * the ca has not been initialized.
  97          */
  98         if (ca->get_info)
  99                 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
 100 }
 101
 102 void tcp_init_congestion_control(struct sock *sk)
 103 {
 104         const struct inet_connection_sock *icsk = inet_csk(sk);
 105
 106         if (icsk->icsk_ca_ops->init)
 107                 icsk->icsk_ca_ops->init(sk);
 108 }
 109
 110 /* Manage refcounts on socket close. */
 111 void tcp_cleanup_congestion_control(struct sock *sk)
 112 {
 113         struct inet_connection_sock *icsk = inet_csk(sk);
 114
 115         if (icsk->icsk_ca_ops->release)
 116                 icsk->icsk_ca_ops->release(sk);
 117         module_put(icsk->icsk_ca_ops->owner);
 118 }
 119
 120 /* Used by sysctl to change default congestion control */
 121 int tcp_set_default_congestion_control(const char *name)
 122 {
 123         struct tcp_congestion_ops *ca;
 124         int ret = -ENOENT;
 125
 126         spin_lock(&tcp_cong_list_lock);
 127         ca = tcp_ca_find(name);
 128 #ifdef CONFIG_MODULES
 129         if (!ca && capable(CAP_NET_ADMIN)) {
 130                 spin_unlock(&tcp_cong_list_lock);
 131
 132                 request_module("tcp_%s", name);
 133                 spin_lock(&tcp_cong_list_lock);
 134                 ca = tcp_ca_find(name);
 135         }
 136 #endif
 137
 138         if (ca) {
 139                 ca->flags |= TCP_CONG_NON_RESTRICTED;   /* default is always allowed */
 140                 list_move(&ca->list, &tcp_cong_list);
 141                 ret = 0;
 142         }
 143         spin_unlock(&tcp_cong_list_lock);
 144
 145         return ret;
 146 }
 147
 148 /* Set default value from kernel configuration at bootup */
 149 static int __init tcp_congestion_default(void)
 150 {
 151         return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
 152 }
 153 late_initcall(tcp_congestion_default);
 154
 155 /* Build string with list of available congestion control values */
 156 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
 157 {
 158         struct tcp_congestion_ops *ca;
 159         size_t offs = 0;
 160
 161         rcu_read_lock();
 162         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 163                 offs += snprintf(buf + offs, maxlen - offs,
 164                                  "%s%s",
 165                                  offs == 0 ? "" : " ", ca->name);
 166         }
 167         rcu_read_unlock();
 168 }
 169
 170 /* Get current default congestion control */
 171 void tcp_get_default_congestion_control(char *name)
 172 {
 173         struct tcp_congestion_ops *ca;
 174         /* We will always have reno... */
 175         BUG_ON(list_empty(&tcp_cong_list));
 176
 177         rcu_read_lock();
 178         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 179         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 180         rcu_read_unlock();
 181 }
 182
 183 /* Built list of non-restricted congestion control values */
 184 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
 185 {
 186         struct tcp_congestion_ops *ca;
 187         size_t offs = 0;
 188
 189         *buf = '\0';
 190         rcu_read_lock();
 191         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 192                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
 193                         continue;
 194                 offs += snprintf(buf + offs, maxlen - offs,
 195                                  "%s%s",
 196                                  offs == 0 ? "" : " ", ca->name);
 197         }
 198         rcu_read_unlock();
 199 }
 200
 201 /* Change list of non-restricted congestion control */
 202 int tcp_set_allowed_congestion_control(char *val)
 203 {
 204         struct tcp_congestion_ops *ca;
 205         char *saved_clone, *clone, *name;
 206         int ret = 0;
 207
 208         saved_clone = clone = kstrdup(val, GFP_USER);
 209         if (!clone)
 210                 return -ENOMEM;
 211
 212         spin_lock(&tcp_cong_list_lock);
 213         /* pass 1 check for bad entries */
 214         while ((name = strsep(&clone, " ")) && *name) {
 215                 ca = tcp_ca_find(name);
 216                 if (!ca) {
 217                         ret = -ENOENT;
 218                         goto out;
 219                 }
 220         }
 221
 222         /* pass 2 clear old values */
 223         list_for_each_entry_rcu(ca, &tcp_cong_list, list)
 224                 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 225
 226         /* pass 3 mark as allowed */
 227         while ((name = strsep(&val, " ")) && *name) {
 228                 ca = tcp_ca_find(name);
 229                 WARN_ON(!ca);
 230                 if (ca)
 231                         ca->flags |= TCP_CONG_NON_RESTRICTED;
 232         }
 233 out:
 234         spin_unlock(&tcp_cong_list_lock);
 235         kfree(saved_clone);
 236
 237         return ret;
 238 }
 239
 240 /* Change congestion control for socket */
 241 int tcp_set_congestion_control(struct sock *sk, const char *name)
 242 {
 243         struct inet_connection_sock *icsk = inet_csk(sk);
 244         struct tcp_congestion_ops *ca;
 245         int err = 0;
 246
 247         rcu_read_lock();
 248         ca = tcp_ca_find(name);
 249
 250         /* no change asking for existing value */
 251         if (ca == icsk->icsk_ca_ops)
 252                 goto out;
 253
 254 #ifdef CONFIG_MODULES
 255         /* not found attempt to autoload module */
 256         if (!ca && capable(CAP_NET_ADMIN)) {
 257                 rcu_read_unlock();
 258                 request_module("tcp_%s", name);
 259                 rcu_read_lock();
 260                 ca = tcp_ca_find(name);
 261         }
 262 #endif
 263         if (!ca)
 264                 err = -ENOENT;
 265
 266         else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
 267                    ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
 268                 err = -EPERM;
 269
 270         else if (!try_module_get(ca->owner))
 271                 err = -EBUSY;
 272
 273         else {
 274                 tcp_cleanup_congestion_control(sk);
 275                 icsk->icsk_ca_ops = ca;
 276
 277                 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
 278                         icsk->icsk_ca_ops->init(sk);
 279         }
 280  out:
 281         rcu_read_unlock();
 282         return err;
 283 }
 284
 285 /* Slow start is used when congestion window is no greater than the slow start
 286  * threshold. We base on RFC2581 and also handle stretch ACKs properly.
 287  * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
 288  * something better;) a packet is only considered (s)acked in its entirety to
 289  * defend the ACK attacks described in the RFC. Slow start processes a stretch
 290  * ACK of degree N as if N acks of degree 1 are received back to back except
 291  * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
 292  * returns the leftover acks to adjust cwnd in congestion avoidance mode.
 293  */
 294 void tcp_slow_start(struct tcp_sock *tp, u32 acked)
 295 {
 296         u32 cwnd = tp->snd_cwnd + acked;
 297
 298         if (cwnd > tp->snd_ssthresh)
 299                 cwnd = tp->snd_ssthresh + 1;
 300         tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
 301 }
 302 EXPORT_SYMBOL_GPL(tcp_slow_start);
 303
 304 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
 305 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
 306 {
 307         if (tp->snd_cwnd_cnt >= w) {
 308                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 309                         tp->snd_cwnd++;
 310                 tp->snd_cwnd_cnt = 0;
 311         } else {
 312                 tp->snd_cwnd_cnt++;
 313         }
 314 }
 315 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 316
 317 /*
 318  * TCP Reno congestion control
 319  * This is special case used for fallback as well.
 320  */
 321 /* This is Jacobson's slow start and congestion avoidance.
 322  * SIGCOMM '88, p. 328.
 323  */
 324 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
 325 {
 326         struct tcp_sock *tp = tcp_sk(sk);
 327
 328         if (!tcp_is_cwnd_limited(sk))
 329                 return;
 330
 331         /* In "safe" area, increase. */
 332         if (tp->snd_cwnd <= tp->snd_ssthresh)
 333                 tcp_slow_start(tp, acked);
 334         /* In dangerous area, increase slowly. */
 335         else
 336                 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
 337 }
 338 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 339
 340 /* Slow start threshold is half the congestion window (min 2) */
 341 u32 tcp_reno_ssthresh(struct sock *sk)
 342 {
 343         const struct tcp_sock *tp = tcp_sk(sk);
 344
 345         return max(tp->snd_cwnd >> 1U, 2U);
 346 }
 347 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 348
 349 struct tcp_congestion_ops tcp_reno = {
 350         .flags          = TCP_CONG_NON_RESTRICTED,
 351         .name           = "reno",
 352         .owner          = THIS_MODULE,
 353         .ssthresh       = tcp_reno_ssthresh,
 354         .cong_avoid     = tcp_reno_cong_avoid,
 355 };