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); 424