1 /* 2 * Plugable 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_init_congestion_control(struct sock *sk) 78 { 79 struct inet_connection_sock *icsk = inet_csk(sk); 80 struct tcp_congestion_ops *ca; 81 82 /* if no choice made yet assign the current value set as default */ 83 if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) { 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 /* fallback to next available */ 92 } 93 rcu_read_unlock(); 94 } 95 96 if (icsk->icsk_ca_ops->init) 97 icsk->icsk_ca_ops->init(sk); 98 } 99 100 /* Manage refcounts on socket close. */ 101 void tcp_cleanup_congestion_control(struct sock *sk) 102 { 103 struct inet_connection_sock *icsk = inet_csk(sk); 104 105 if (icsk->icsk_ca_ops->release) 106 icsk->icsk_ca_ops->release(sk); 107 module_put(icsk->icsk_ca_ops->owner); 108 } 109 110 /* Used by sysctl to change default congestion control */ 111 int tcp_set_default_congestion_control(const char *name) 112 { 113 struct tcp_congestion_ops *ca; 114 int ret = -ENOENT; 115 116 spin_lock(&tcp_cong_list_lock); 117 ca = tcp_ca_find(name); 118 #ifdef CONFIG_MODULES 119 if (!ca && capable(CAP_NET_ADMIN)) { 120 spin_unlock(&tcp_cong_list_lock); 121 122 request_module("tcp_%s", name); 123 spin_lock(&tcp_cong_list_lock); 124 ca = tcp_ca_find(name); 125 } 126 #endif 127 128 if (ca) { 129 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */ 130 list_move(&ca->list, &tcp_cong_list); 131 ret = 0; 132 } 133 spin_unlock(&tcp_cong_list_lock); 134 135 return ret; 136 } 137 138 /* Set default value from kernel configuration at bootup */ 139 static int __init tcp_congestion_default(void) 140 { 141 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG); 142 } 143 late_initcall(tcp_congestion_default); 144 145 146 /* Build string with list of available congestion control values */ 147 void tcp_get_available_congestion_control(char *buf, size_t maxlen) 148 { 149 struct tcp_congestion_ops *ca; 150 size_t offs = 0; 151 152 rcu_read_lock(); 153 list_for_each_entry_rcu(ca, &tcp_cong_list, list) { 154 offs += snprintf(buf + offs, maxlen - offs, 155 "%s%s", 156 offs == 0 ? "" : " ", ca->name); 157 158 } 159 rcu_read_unlock(); 160 } 161 162 /* Get current default congestion control */ 163 void tcp_get_default_congestion_control(char *name) 164 { 165 struct tcp_congestion_ops *ca; 166 /* We will always have reno... */ 167 BUG_ON(list_empty(&tcp_cong_list)); 168 169 rcu_read_lock(); 170 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list); 171 strncpy(name, ca->name, TCP_CA_NAME_MAX); 172 rcu_read_unlock(); 173 } 174 175 /* Built list of non-restricted congestion control values */ 176 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen) 177 { 178 struct tcp_congestion_ops *ca; 179 size_t offs = 0; 180 181 *buf = '\0'; 182 rcu_read_lock(); 183 list_for_each_entry_rcu(ca, &tcp_cong_list, list) { 184 if (!(ca->flags & TCP_CONG_NON_RESTRICTED)) 185 continue; 186 offs += snprintf(buf + offs, maxlen - offs, 187 "%s%s", 188 offs == 0 ? "" : " ", ca->name); 189 190 } 191 rcu_read_unlock(); 192 } 193 194 /* Change list of non-restricted congestion control */ 195 int tcp_set_allowed_congestion_control(char *val) 196 { 197 struct tcp_congestion_ops *ca; 198 char *saved_clone, *clone, *name; 199 int ret = 0; 200 201 saved_clone = clone = kstrdup(val, GFP_USER); 202 if (!clone) 203 return -ENOMEM; 204 205 spin_lock(&tcp_cong_list_lock); 206 /* pass 1 check for bad entries */ 207 while ((name = strsep(&clone, " ")) && *name) { 208 ca = tcp_ca_find(name); 209 if (!ca) { 210 ret = -ENOENT; 211 goto out; 212 } 213 } 214 215 /* pass 2 clear old values */ 216 list_for_each_entry_rcu(ca, &tcp_cong_list, list) 217 ca->flags &= ~TCP_CONG_NON_RESTRICTED; 218 219 /* pass 3 mark as allowed */ 220 while ((name = strsep(&val, " ")) && *name) { 221 ca = tcp_ca_find(name); 222 WARN_ON(!ca); 223 if (ca) 224 ca->flags |= TCP_CONG_NON_RESTRICTED; 225 } 226 out: 227 spin_unlock(&tcp_cong_list_lock); 228 kfree(saved_clone); 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) || 261 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) 262 err = -EPERM; 263 264 else if (!try_module_get(ca->owner)) 265 err = -EBUSY; 266 267 else { 268 tcp_cleanup_congestion_control(sk); 269 icsk->icsk_ca_ops = ca; 270 271 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init) 272 icsk->icsk_ca_ops->init(sk); 273 } 274 out: 275 rcu_read_unlock(); 276 return err; 277 } 278 279 /* RFC2861 Check whether we are limited by application or congestion window 280 * This is the inverse of cwnd check in tcp_tso_should_defer 281 */ 282 bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight) 283 { 284 const struct tcp_sock *tp = tcp_sk(sk); 285 u32 left; 286 287 if (in_flight >= tp->snd_cwnd) 288 return true; 289 290 left = tp->snd_cwnd - in_flight; 291 if (sk_can_gso(sk) && 292 left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd && 293 left * tp->mss_cache < sk->sk_gso_max_size && 294 left < sk->sk_gso_max_segs) 295 return true; 296 return left <= tcp_max_tso_deferred_mss(tp); 297 } 298 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited); 299 300 /* Slow start is used when congestion window is no greater than the slow start 301 * threshold. We base on RFC2581 and also handle stretch ACKs properly. 302 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but 303 * something better;) a packet is only considered (s)acked in its entirety to 304 * defend the ACK attacks described in the RFC. Slow start processes a stretch 305 * ACK of degree N as if N acks of degree 1 are received back to back except 306 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and 307 * returns the leftover acks to adjust cwnd in congestion avoidance mode. 308 */ 309 int tcp_slow_start(struct tcp_sock *tp, u32 acked) 310 { 311 u32 cwnd = tp->snd_cwnd + acked; 312 313 if (cwnd > tp->snd_ssthresh) 314 cwnd = tp->snd_ssthresh + 1; 315 acked -= cwnd - tp->snd_cwnd; 316 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp); 317 return acked; 318 } 319 EXPORT_SYMBOL_GPL(tcp_slow_start); 320 321 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */ 322 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w) 323 { 324 if (tp->snd_cwnd_cnt >= w) { 325 if (tp->snd_cwnd < tp->snd_cwnd_clamp) 326 tp->snd_cwnd++; 327 tp->snd_cwnd_cnt = 0; 328 } else { 329 tp->snd_cwnd_cnt++; 330 } 331 } 332 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai); 333 334 /* 335 * TCP Reno congestion control 336 * This is special case used for fallback as well. 337 */ 338 /* This is Jacobson's slow start and congestion avoidance. 339 * SIGCOMM '88, p. 328. 340 */ 341 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight) 342 { 343 struct tcp_sock *tp = tcp_sk(sk); 344 345 if (!tcp_is_cwnd_limited(sk, in_flight)) 346 return; 347 348 /* In "safe" area, increase. */ 349 if (tp->snd_cwnd <= tp->snd_ssthresh) 350 tcp_slow_start(tp, acked); 351 /* In dangerous area, increase slowly. */ 352 else 353 tcp_cong_avoid_ai(tp, tp->snd_cwnd); 354 } 355 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid); 356 357 /* Slow start threshold is half the congestion window (min 2) */ 358 u32 tcp_reno_ssthresh(struct sock *sk) 359 { 360 const struct tcp_sock *tp = tcp_sk(sk); 361 return max(tp->snd_cwnd >> 1U, 2U); 362 } 363 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh); 364 365 /* Lower bound on congestion window with halving. */ 366 u32 tcp_reno_min_cwnd(const struct sock *sk) 367 { 368 const struct tcp_sock *tp = tcp_sk(sk); 369 return tp->snd_ssthresh/2; 370 } 371 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd); 372 373 struct tcp_congestion_ops tcp_reno = { 374 .flags = TCP_CONG_NON_RESTRICTED, 375 .name = "reno", 376 .owner = THIS_MODULE, 377 .ssthresh = tcp_reno_ssthresh, 378 .cong_avoid = tcp_reno_cong_avoid, 379 .min_cwnd = tcp_reno_min_cwnd, 380 }; 381 382 /* Initial congestion control used (until SYN) 383 * really reno under another name so we can tell difference 384 * during tcp_set_default_congestion_control 385 */ 386 struct tcp_congestion_ops tcp_init_congestion_ops = { 387 .name = "", 388 .owner = THIS_MODULE, 389 .ssthresh = tcp_reno_ssthresh, 390 .cong_avoid = tcp_reno_cong_avoid, 391 .min_cwnd = tcp_reno_min_cwnd, 392 }; 393 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops); 394