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