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/config.h>
  10 #include <linux/module.h>
  11 #include <linux/mm.h>
  12 #include <linux/types.h>
  13 #include <linux/list.h>
  14 #include <net/tcp.h>
  15
  16 static DEFINE_SPINLOCK(tcp_cong_list_lock);
  17 static LIST_HEAD(tcp_cong_list);
  18
  19 /* Simple linear search, don't expect many entries! */
  20 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
  21 {
  22         struct tcp_congestion_ops *e;
  23
  24         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
  25                 if (strcmp(e->name, name) == 0)
  26                         return e;
  27         }
  28
  29         return NULL;
  30 }
  31
  32 /*
  33  * Attach new congestion control algorthim to the list
  34  * of available options.
  35  */
  36 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
  37 {
  38         int ret = 0;
  39
  40         /* all algorithms must implement ssthresh and cong_avoid ops */
  41         if (!ca->ssthresh || !ca->cong_avoid || !ca->min_cwnd) {
  42                 printk(KERN_ERR "TCP %s does not implement required ops\n",
  43                        ca->name);
  44                 return -EINVAL;
  45         }
  46
  47         spin_lock(&tcp_cong_list_lock);
  48         if (tcp_ca_find(ca->name)) {
  49                 printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
  50                 ret = -EEXIST;
  51         } else {
  52                 list_add_rcu(&ca->list, &tcp_cong_list);
  53                 printk(KERN_INFO "TCP %s registered\n", ca->name);
  54         }
  55         spin_unlock(&tcp_cong_list_lock);
  56
  57         return ret;
  58 }
  59 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
  60
  61 /*
  62  * Remove congestion control algorithm, called from
  63  * the module's remove function.  Module ref counts are used
  64  * to ensure that this can't be done till all sockets using
  65  * that method are closed.
  66  */
  67 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
  68 {
  69         spin_lock(&tcp_cong_list_lock);
  70         list_del_rcu(&ca->list);
  71         spin_unlock(&tcp_cong_list_lock);
  72 }
  73 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
  74
  75 /* Assign choice of congestion control. */
  76 void tcp_init_congestion_control(struct sock *sk)
  77 {
  78         struct inet_connection_sock *icsk = inet_csk(sk);
  79         struct tcp_congestion_ops *ca;
  80
  81         if (icsk->icsk_ca_ops != &tcp_init_congestion_ops)
  82                 return;
  83
  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         }
  92         rcu_read_unlock();
  93
  94         if (icsk->icsk_ca_ops->init)
  95                 icsk->icsk_ca_ops->init(sk);
  96 }
  97
  98 /* Manage refcounts on socket close. */
  99 void tcp_cleanup_congestion_control(struct sock *sk)
 100 {
 101         struct inet_connection_sock *icsk = inet_csk(sk);
 102
 103         if (icsk->icsk_ca_ops->release)
 104                 icsk->icsk_ca_ops->release(sk);
 105         module_put(icsk->icsk_ca_ops->owner);
 106 }
 107
 108 /* Used by sysctl to change default congestion control */
 109 int tcp_set_default_congestion_control(const char *name)
 110 {
 111         struct tcp_congestion_ops *ca;
 112         int ret = -ENOENT;
 113
 114         spin_lock(&tcp_cong_list_lock);
 115         ca = tcp_ca_find(name);
 116 #ifdef CONFIG_KMOD
 117         if (!ca) {
 118                 spin_unlock(&tcp_cong_list_lock);
 119
 120                 request_module("tcp_%s", name);
 121                 spin_lock(&tcp_cong_list_lock);
 122                 ca = tcp_ca_find(name);
 123         }
 124 #endif
 125
 126         if (ca) {
 127                 list_move(&ca->list, &tcp_cong_list);
 128                 ret = 0;
 129         }
 130         spin_unlock(&tcp_cong_list_lock);
 131
 132         return ret;
 133 }
 134
 135 /* Get current default congestion control */
 136 void tcp_get_default_congestion_control(char *name)
 137 {
 138         struct tcp_congestion_ops *ca;
 139         /* We will always have reno... */
 140         BUG_ON(list_empty(&tcp_cong_list));
 141
 142         rcu_read_lock();
 143         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
 144         strncpy(name, ca->name, TCP_CA_NAME_MAX);
 145         rcu_read_unlock();
 146 }
 147
 148 /* Change congestion control for socket */
 149 int tcp_set_congestion_control(struct sock *sk, const char *name)
 150 {
 151         struct inet_connection_sock *icsk = inet_csk(sk);
 152         struct tcp_congestion_ops *ca;
 153         int err = 0;
 154
 155         rcu_read_lock();
 156         ca = tcp_ca_find(name);
 157         if (ca == icsk->icsk_ca_ops)
 158                 goto out;
 159
 160         if (!ca)
 161                 err = -ENOENT;
 162
 163         else if (!try_module_get(ca->owner))
 164                 err = -EBUSY;
 165
 166         else {
 167                 tcp_cleanup_congestion_control(sk);
 168                 icsk->icsk_ca_ops = ca;
 169                 if (icsk->icsk_ca_ops->init)
 170                         icsk->icsk_ca_ops->init(sk);
 171         }
 172  out:
 173         rcu_read_unlock();
 174         return err;
 175 }
 176
 177
 178 /*
 179  * Linear increase during slow start
 180  */
 181 void tcp_slow_start(struct tcp_sock *tp)
 182 {
 183         if (sysctl_tcp_abc) {
 184                 /* RFC3465: Slow Start
 185                  * TCP sender SHOULD increase cwnd by the number of
 186                  * previously unacknowledged bytes ACKed by each incoming
 187                  * acknowledgment, provided the increase is not more than L
 188                  */
 189                 if (tp->bytes_acked < tp->mss_cache)
 190                         return;
 191
 192                 /* We MAY increase by 2 if discovered delayed ack */
 193                 if (sysctl_tcp_abc > 1 && tp->bytes_acked > 2*tp->mss_cache) {
 194                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 195                                 tp->snd_cwnd++;
 196                 }
 197         }
 198         tp->bytes_acked = 0;
 199
 200         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 201                 tp->snd_cwnd++;
 202 }
 203 EXPORT_SYMBOL_GPL(tcp_slow_start);
 204
 205 /*
 206  * TCP Reno congestion control
 207  * This is special case used for fallback as well.
 208  */
 209 /* This is Jacobson's slow start and congestion avoidance.
 210  * SIGCOMM '88, p. 328.
 211  */
 212 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
 213                          int flag)
 214 {
 215         struct tcp_sock *tp = tcp_sk(sk);
 216
 217         if (!tcp_is_cwnd_limited(sk, in_flight))
 218                 return;
 219
 220         /* In "safe" area, increase. */
 221         if (tp->snd_cwnd <= tp->snd_ssthresh)
 222                 tcp_slow_start(tp);
 223
 224         /* In dangerous area, increase slowly. */
 225         else if (sysctl_tcp_abc) {
 226                 /* RFC3465: Appropriate Byte Count
 227                  * increase once for each full cwnd acked
 228                  */
 229                 if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
 230                         tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
 231                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 232                                 tp->snd_cwnd++;
 233                 }
 234         } else {
 235                 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */
 236                 if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
 237                         if (tp->snd_cwnd < tp->snd_cwnd_clamp)
 238                                 tp->snd_cwnd++;
 239                         tp->snd_cwnd_cnt = 0;
 240                 } else
 241                         tp->snd_cwnd_cnt++;
 242         }
 243 }
 244 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 245
 246 /* Slow start threshold is half the congestion window (min 2) */
 247 u32 tcp_reno_ssthresh(struct sock *sk)
 248 {
 249         const struct tcp_sock *tp = tcp_sk(sk);
 250         return max(tp->snd_cwnd >> 1U, 2U);
 251 }
 252 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 253
 254 /* Lower bound on congestion window. */
 255 u32 tcp_reno_min_cwnd(struct sock *sk)
 256 {
 257         const struct tcp_sock *tp = tcp_sk(sk);
 258         return tp->snd_ssthresh/2;
 259 }
 260 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
 261
 262 struct tcp_congestion_ops tcp_reno = {
 263         .name           = "reno",
 264         .owner          = THIS_MODULE,
 265         .ssthresh       = tcp_reno_ssthresh,
 266         .cong_avoid     = tcp_reno_cong_avoid,
 267         .min_cwnd       = tcp_reno_min_cwnd,
 268 };
 269
 270 /* Initial congestion control used (until SYN)
 271  * really reno under another name so we can tell difference
 272  * during tcp_set_default_congestion_control
 273  */
 274 struct tcp_congestion_ops tcp_init_congestion_ops  = {
 275         .name           = "",
 276         .owner          = THIS_MODULE,
 277         .ssthresh       = tcp_reno_ssthresh,
 278         .cong_avoid     = tcp_reno_cong_avoid,
 279         .min_cwnd       = tcp_reno_min_cwnd,
 280 };
 281 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);