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_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 }; 356