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Linux/net/ipv4/tcp_cong.c

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  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 int sysctl_tcp_max_ssthresh = 0;
 19 
 20 static DEFINE_SPINLOCK(tcp_cong_list_lock);
 21 static LIST_HEAD(tcp_cong_list);
 22 
 23 /* Simple linear search, don't expect many entries! */
 24 static struct tcp_congestion_ops *tcp_ca_find(const char *name)
 25 {
 26         struct tcp_congestion_ops *e;
 27 
 28         list_for_each_entry_rcu(e, &tcp_cong_list, list) {
 29                 if (strcmp(e->name, name) == 0)
 30                         return e;
 31         }
 32 
 33         return NULL;
 34 }
 35 
 36 /*
 37  * Attach new congestion control algorithm to the list
 38  * of available options.
 39  */
 40 int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
 41 {
 42         int ret = 0;
 43 
 44         /* all algorithms must implement ssthresh and cong_avoid ops */
 45         if (!ca->ssthresh || !ca->cong_avoid) {
 46                 pr_err("%s does not implement required ops\n", ca->name);
 47                 return -EINVAL;
 48         }
 49 
 50         spin_lock(&tcp_cong_list_lock);
 51         if (tcp_ca_find(ca->name)) {
 52                 pr_notice("%s already registered\n", ca->name);
 53                 ret = -EEXIST;
 54         } else {
 55                 list_add_tail_rcu(&ca->list, &tcp_cong_list);
 56                 pr_info("%s registered\n", ca->name);
 57         }
 58         spin_unlock(&tcp_cong_list_lock);
 59 
 60         return ret;
 61 }
 62 EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
 63 
 64 /*
 65  * Remove congestion control algorithm, called from
 66  * the module's remove function.  Module ref counts are used
 67  * to ensure that this can't be done till all sockets using
 68  * that method are closed.
 69  */
 70 void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
 71 {
 72         spin_lock(&tcp_cong_list_lock);
 73         list_del_rcu(&ca->list);
 74         spin_unlock(&tcp_cong_list_lock);
 75 }
 76 EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
 77 
 78 /* Assign choice of congestion control. */
 79 void tcp_init_congestion_control(struct sock *sk)
 80 {
 81         struct inet_connection_sock *icsk = inet_csk(sk);
 82         struct tcp_congestion_ops *ca;
 83 
 84         /* if no choice made yet assign the current value set as default */
 85         if (icsk->icsk_ca_ops == &tcp_init_congestion_ops) {
 86                 rcu_read_lock();
 87                 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
 88                         if (try_module_get(ca->owner)) {
 89                                 icsk->icsk_ca_ops = ca;
 90                                 break;
 91                         }
 92 
 93                         /* fallback to next available */
 94                 }
 95                 rcu_read_unlock();
 96         }
 97 
 98         if (icsk->icsk_ca_ops->init)
 99                 icsk->icsk_ca_ops->init(sk);
100 }
101 
102 /* Manage refcounts on socket close. */
103 void tcp_cleanup_congestion_control(struct sock *sk)
104 {
105         struct inet_connection_sock *icsk = inet_csk(sk);
106 
107         if (icsk->icsk_ca_ops->release)
108                 icsk->icsk_ca_ops->release(sk);
109         module_put(icsk->icsk_ca_ops->owner);
110 }
111 
112 /* Used by sysctl to change default congestion control */
113 int tcp_set_default_congestion_control(const char *name)
114 {
115         struct tcp_congestion_ops *ca;
116         int ret = -ENOENT;
117 
118         spin_lock(&tcp_cong_list_lock);
119         ca = tcp_ca_find(name);
120 #ifdef CONFIG_MODULES
121         if (!ca && capable(CAP_NET_ADMIN)) {
122                 spin_unlock(&tcp_cong_list_lock);
123 
124                 request_module("tcp_%s", name);
125                 spin_lock(&tcp_cong_list_lock);
126                 ca = tcp_ca_find(name);
127         }
128 #endif
129 
130         if (ca) {
131                 ca->flags |= TCP_CONG_NON_RESTRICTED;   /* default is always allowed */
132                 list_move(&ca->list, &tcp_cong_list);
133                 ret = 0;
134         }
135         spin_unlock(&tcp_cong_list_lock);
136 
137         return ret;
138 }
139 
140 /* Set default value from kernel configuration at bootup */
141 static int __init tcp_congestion_default(void)
142 {
143         return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
144 }
145 late_initcall(tcp_congestion_default);
146 
147 
148 /* Build string with list of available congestion control values */
149 void tcp_get_available_congestion_control(char *buf, size_t maxlen)
150 {
151         struct tcp_congestion_ops *ca;
152         size_t offs = 0;
153 
154         rcu_read_lock();
155         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
156                 offs += snprintf(buf + offs, maxlen - offs,
157                                  "%s%s",
158                                  offs == 0 ? "" : " ", ca->name);
159 
160         }
161         rcu_read_unlock();
162 }
163 
164 /* Get current default congestion control */
165 void tcp_get_default_congestion_control(char *name)
166 {
167         struct tcp_congestion_ops *ca;
168         /* We will always have reno... */
169         BUG_ON(list_empty(&tcp_cong_list));
170 
171         rcu_read_lock();
172         ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
173         strncpy(name, ca->name, TCP_CA_NAME_MAX);
174         rcu_read_unlock();
175 }
176 
177 /* Built list of non-restricted congestion control values */
178 void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
179 {
180         struct tcp_congestion_ops *ca;
181         size_t offs = 0;
182 
183         *buf = '\0';
184         rcu_read_lock();
185         list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
186                 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
187                         continue;
188                 offs += snprintf(buf + offs, maxlen - offs,
189                                  "%s%s",
190                                  offs == 0 ? "" : " ", ca->name);
191 
192         }
193         rcu_read_unlock();
194 }
195 
196 /* Change list of non-restricted congestion control */
197 int tcp_set_allowed_congestion_control(char *val)
198 {
199         struct tcp_congestion_ops *ca;
200         char *saved_clone, *clone, *name;
201         int ret = 0;
202 
203         saved_clone = clone = kstrdup(val, GFP_USER);
204         if (!clone)
205                 return -ENOMEM;
206 
207         spin_lock(&tcp_cong_list_lock);
208         /* pass 1 check for bad entries */
209         while ((name = strsep(&clone, " ")) && *name) {
210                 ca = tcp_ca_find(name);
211                 if (!ca) {
212                         ret = -ENOENT;
213                         goto out;
214                 }
215         }
216 
217         /* pass 2 clear old values */
218         list_for_each_entry_rcu(ca, &tcp_cong_list, list)
219                 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
220 
221         /* pass 3 mark as allowed */
222         while ((name = strsep(&val, " ")) && *name) {
223                 ca = tcp_ca_find(name);
224                 WARN_ON(!ca);
225                 if (ca)
226                         ca->flags |= TCP_CONG_NON_RESTRICTED;
227         }
228 out:
229         spin_unlock(&tcp_cong_list_lock);
230         kfree(saved_clone);
231 
232         return ret;
233 }
234 
235 
236 /* Change congestion control for socket */
237 int tcp_set_congestion_control(struct sock *sk, const char *name)
238 {
239         struct inet_connection_sock *icsk = inet_csk(sk);
240         struct tcp_congestion_ops *ca;
241         int err = 0;
242 
243         rcu_read_lock();
244         ca = tcp_ca_find(name);
245 
246         /* no change asking for existing value */
247         if (ca == icsk->icsk_ca_ops)
248                 goto out;
249 
250 #ifdef CONFIG_MODULES
251         /* not found attempt to autoload module */
252         if (!ca && capable(CAP_NET_ADMIN)) {
253                 rcu_read_unlock();
254                 request_module("tcp_%s", name);
255                 rcu_read_lock();
256                 ca = tcp_ca_find(name);
257         }
258 #endif
259         if (!ca)
260                 err = -ENOENT;
261 
262         else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
263                    ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
264                 err = -EPERM;
265 
266         else if (!try_module_get(ca->owner))
267                 err = -EBUSY;
268 
269         else {
270                 tcp_cleanup_congestion_control(sk);
271                 icsk->icsk_ca_ops = ca;
272 
273                 if (sk->sk_state != TCP_CLOSE && icsk->icsk_ca_ops->init)
274                         icsk->icsk_ca_ops->init(sk);
275         }
276  out:
277         rcu_read_unlock();
278         return err;
279 }
280 
281 /* RFC2861 Check whether we are limited by application or congestion window
282  * This is the inverse of cwnd check in tcp_tso_should_defer
283  */
284 bool tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
285 {
286         const struct tcp_sock *tp = tcp_sk(sk);
287         u32 left;
288 
289         if (in_flight >= tp->snd_cwnd)
290                 return true;
291 
292         left = tp->snd_cwnd - in_flight;
293         if (sk_can_gso(sk) &&
294             left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
295             left * tp->mss_cache < sk->sk_gso_max_size &&
296             left < sk->sk_gso_max_segs)
297                 return true;
298         return left <= tcp_max_tso_deferred_mss(tp);
299 }
300 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
301 
302 /*
303  * Slow start is used when congestion window is less than slow start
304  * threshold. This version implements the basic RFC2581 version
305  * and optionally supports:
306  *      RFC3742 Limited Slow Start        - growth limited to max_ssthresh
307  *      RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged
308  */
309 void tcp_slow_start(struct tcp_sock *tp)
310 {
311         int cnt; /* increase in packets */
312         unsigned int delta = 0;
313         u32 snd_cwnd = tp->snd_cwnd;
314 
315         if (unlikely(!snd_cwnd)) {
316                 pr_err_once("snd_cwnd is nul, please report this bug.\n");
317                 snd_cwnd = 1U;
318         }
319 
320         if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
321                 cnt = sysctl_tcp_max_ssthresh >> 1;     /* limited slow start */
322         else
323                 cnt = snd_cwnd;                         /* exponential increase */
324 
325         tp->snd_cwnd_cnt += cnt;
326         while (tp->snd_cwnd_cnt >= snd_cwnd) {
327                 tp->snd_cwnd_cnt -= snd_cwnd;
328                 delta++;
329         }
330         tp->snd_cwnd = min(snd_cwnd + delta, tp->snd_cwnd_clamp);
331 }
332 EXPORT_SYMBOL_GPL(tcp_slow_start);
333 
334 /* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
335 void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
336 {
337         if (tp->snd_cwnd_cnt >= w) {
338                 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
339                         tp->snd_cwnd++;
340                 tp->snd_cwnd_cnt = 0;
341         } else {
342                 tp->snd_cwnd_cnt++;
343         }
344 }
345 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
346 
347 /*
348  * TCP Reno congestion control
349  * This is special case used for fallback as well.
350  */
351 /* This is Jacobson's slow start and congestion avoidance.
352  * SIGCOMM '88, p. 328.
353  */
354 void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
355 {
356         struct tcp_sock *tp = tcp_sk(sk);
357 
358         if (!tcp_is_cwnd_limited(sk, in_flight))
359                 return;
360 
361         /* In "safe" area, increase. */
362         if (tp->snd_cwnd <= tp->snd_ssthresh)
363                 tcp_slow_start(tp);
364         /* In dangerous area, increase slowly. */
365         else
366                 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
367 }
368 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
369 
370 /* Slow start threshold is half the congestion window (min 2) */
371 u32 tcp_reno_ssthresh(struct sock *sk)
372 {
373         const struct tcp_sock *tp = tcp_sk(sk);
374         return max(tp->snd_cwnd >> 1U, 2U);
375 }
376 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
377 
378 /* Lower bound on congestion window with halving. */
379 u32 tcp_reno_min_cwnd(const struct sock *sk)
380 {
381         const struct tcp_sock *tp = tcp_sk(sk);
382         return tp->snd_ssthresh/2;
383 }
384 EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
385 
386 struct tcp_congestion_ops tcp_reno = {
387         .flags          = TCP_CONG_NON_RESTRICTED,
388         .name           = "reno",
389         .owner          = THIS_MODULE,
390         .ssthresh       = tcp_reno_ssthresh,
391         .cong_avoid     = tcp_reno_cong_avoid,
392         .min_cwnd       = tcp_reno_min_cwnd,
393 };
394 
395 /* Initial congestion control used (until SYN)
396  * really reno under another name so we can tell difference
397  * during tcp_set_default_congestion_control
398  */
399 struct tcp_congestion_ops tcp_init_congestion_ops  = {
400         .name           = "",
401         .owner          = THIS_MODULE,
402         .ssthresh       = tcp_reno_ssthresh,
403         .cong_avoid     = tcp_reno_cong_avoid,
404         .min_cwnd       = tcp_reno_min_cwnd,
405 };
406 EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
407 

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