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1/*
2 * Pluggable 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 <linux/jhash.h>
17#include <net/tcp.h>
18
19static DEFINE_SPINLOCK(tcp_cong_list_lock);
20static LIST_HEAD(tcp_cong_list);
21
22/* Simple linear search, don't expect many entries! */
23static struct tcp_congestion_ops *tcp_ca_find(const char *name)
24{
25 struct tcp_congestion_ops *e;
26
27 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
28 if (strcmp(e->name, name) == 0)
29 return e;
30 }
31
32 return NULL;
33}
34
35/* Must be called with rcu lock held */
36static const struct tcp_congestion_ops *__tcp_ca_find_autoload(const char *name)
37{
38 const struct tcp_congestion_ops *ca = tcp_ca_find(name);
39#ifdef CONFIG_MODULES
40 if (!ca && capable(CAP_NET_ADMIN)) {
41 rcu_read_unlock();
42 request_module("tcp_%s", name);
43 rcu_read_lock();
44 ca = tcp_ca_find(name);
45 }
46#endif
47 return ca;
48}
49
50/* Simple linear search, not much in here. */
51struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
52{
53 struct tcp_congestion_ops *e;
54
55 list_for_each_entry_rcu(e, &tcp_cong_list, list) {
56 if (e->key == key)
57 return e;
58 }
59
60 return NULL;
61}
62
63/*
64 * Attach new congestion control algorithm to the list
65 * of available options.
66 */
67int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
68{
69 int ret = 0;
70
71 /* all algorithms must implement ssthresh and cong_avoid ops */
72 if (!ca->ssthresh || !ca->cong_avoid) {
73 pr_err("%s does not implement required ops\n", ca->name);
74 return -EINVAL;
75 }
76
77 ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name));
78
79 spin_lock(&tcp_cong_list_lock);
80 if (ca->key == TCP_CA_UNSPEC || tcp_ca_find_key(ca->key)) {
81 pr_notice("%s already registered or non-unique key\n",
82 ca->name);
83 ret = -EEXIST;
84 } else {
85 list_add_tail_rcu(&ca->list, &tcp_cong_list);
86 pr_debug("%s registered\n", ca->name);
87 }
88 spin_unlock(&tcp_cong_list_lock);
89
90 return ret;
91}
92EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
93
94/*
95 * Remove congestion control algorithm, called from
96 * the module's remove function. Module ref counts are used
97 * to ensure that this can't be done till all sockets using
98 * that method are closed.
99 */
100void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
101{
102 spin_lock(&tcp_cong_list_lock);
103 list_del_rcu(&ca->list);
104 spin_unlock(&tcp_cong_list_lock);
105
106 /* Wait for outstanding readers to complete before the
107 * module gets removed entirely.
108 *
109 * A try_module_get() should fail by now as our module is
110 * in "going" state since no refs are held anymore and
111 * module_exit() handler being called.
112 */
113 synchronize_rcu();
114}
115EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
116
117u32 tcp_ca_get_key_by_name(const char *name, bool *ecn_ca)
118{
119 const struct tcp_congestion_ops *ca;
120 u32 key = TCP_CA_UNSPEC;
121
122 might_sleep();
123
124 rcu_read_lock();
125 ca = __tcp_ca_find_autoload(name);
126 if (ca) {
127 key = ca->key;
128 *ecn_ca = ca->flags & TCP_CONG_NEEDS_ECN;
129 }
130 rcu_read_unlock();
131
132 return key;
133}
134EXPORT_SYMBOL_GPL(tcp_ca_get_key_by_name);
135
136char *tcp_ca_get_name_by_key(u32 key, char *buffer)
137{
138 const struct tcp_congestion_ops *ca;
139 char *ret = NULL;
140
141 rcu_read_lock();
142 ca = tcp_ca_find_key(key);
143 if (ca)
144 ret = strncpy(buffer, ca->name,
145 TCP_CA_NAME_MAX);
146 rcu_read_unlock();
147
148 return ret;
149}
150EXPORT_SYMBOL_GPL(tcp_ca_get_name_by_key);
151
152/* Assign choice of congestion control. */
153void tcp_assign_congestion_control(struct sock *sk)
154{
155 struct inet_connection_sock *icsk = inet_csk(sk);
156 struct tcp_congestion_ops *ca;
157
158 rcu_read_lock();
159 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
160 if (likely(try_module_get(ca->owner))) {
161 icsk->icsk_ca_ops = ca;
162 goto out;
163 }
164 /* Fallback to next available. The last really
165 * guaranteed fallback is Reno from this list.
166 */
167 }
168out:
169 rcu_read_unlock();
170
171 /* Clear out private data before diag gets it and
172 * the ca has not been initialized.
173 */
174 if (ca->get_info)
175 memset(icsk->icsk_ca_priv, 0, sizeof(icsk->icsk_ca_priv));
176 if (ca->flags & TCP_CONG_NEEDS_ECN)
177 INET_ECN_xmit(sk);
178 else
179 INET_ECN_dontxmit(sk);
180}
181
182void tcp_init_congestion_control(struct sock *sk)
183{
184 const struct inet_connection_sock *icsk = inet_csk(sk);
185
186 if (icsk->icsk_ca_ops->init)
187 icsk->icsk_ca_ops->init(sk);
188 if (tcp_ca_needs_ecn(sk))
189 INET_ECN_xmit(sk);
190 else
191 INET_ECN_dontxmit(sk);
192}
193
194static void tcp_reinit_congestion_control(struct sock *sk,
195 const struct tcp_congestion_ops *ca)
196{
197 struct inet_connection_sock *icsk = inet_csk(sk);
198
199 tcp_cleanup_congestion_control(sk);
200 icsk->icsk_ca_ops = ca;
201 icsk->icsk_ca_setsockopt = 1;
202
203 if (sk->sk_state != TCP_CLOSE)
204 tcp_init_congestion_control(sk);
205}
206
207/* Manage refcounts on socket close. */
208void tcp_cleanup_congestion_control(struct sock *sk)
209{
210 struct inet_connection_sock *icsk = inet_csk(sk);
211
212 if (icsk->icsk_ca_ops->release)
213 icsk->icsk_ca_ops->release(sk);
214 module_put(icsk->icsk_ca_ops->owner);
215}
216
217/* Used by sysctl to change default congestion control */
218int tcp_set_default_congestion_control(const char *name)
219{
220 struct tcp_congestion_ops *ca;
221 int ret = -ENOENT;
222
223 spin_lock(&tcp_cong_list_lock);
224 ca = tcp_ca_find(name);
225#ifdef CONFIG_MODULES
226 if (!ca && capable(CAP_NET_ADMIN)) {
227 spin_unlock(&tcp_cong_list_lock);
228
229 request_module("tcp_%s", name);
230 spin_lock(&tcp_cong_list_lock);
231 ca = tcp_ca_find(name);
232 }
233#endif
234
235 if (ca) {
236 ca->flags |= TCP_CONG_NON_RESTRICTED; /* default is always allowed */
237 list_move(&ca->list, &tcp_cong_list);
238 ret = 0;
239 }
240 spin_unlock(&tcp_cong_list_lock);
241
242 return ret;
243}
244
245/* Set default value from kernel configuration at bootup */
246static int __init tcp_congestion_default(void)
247{
248 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
249}
250late_initcall(tcp_congestion_default);
251
252/* Build string with list of available congestion control values */
253void tcp_get_available_congestion_control(char *buf, size_t maxlen)
254{
255 struct tcp_congestion_ops *ca;
256 size_t offs = 0;
257
258 rcu_read_lock();
259 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
260 offs += snprintf(buf + offs, maxlen - offs,
261 "%s%s",
262 offs == 0 ? "" : " ", ca->name);
263 }
264 rcu_read_unlock();
265}
266
267/* Get current default congestion control */
268void tcp_get_default_congestion_control(char *name)
269{
270 struct tcp_congestion_ops *ca;
271 /* We will always have reno... */
272 BUG_ON(list_empty(&tcp_cong_list));
273
274 rcu_read_lock();
275 ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
276 strncpy(name, ca->name, TCP_CA_NAME_MAX);
277 rcu_read_unlock();
278}
279
280/* Built list of non-restricted congestion control values */
281void tcp_get_allowed_congestion_control(char *buf, size_t maxlen)
282{
283 struct tcp_congestion_ops *ca;
284 size_t offs = 0;
285
286 *buf = '\0';
287 rcu_read_lock();
288 list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
289 if (!(ca->flags & TCP_CONG_NON_RESTRICTED))
290 continue;
291 offs += snprintf(buf + offs, maxlen - offs,
292 "%s%s",
293 offs == 0 ? "" : " ", ca->name);
294 }
295 rcu_read_unlock();
296}
297
298/* Change list of non-restricted congestion control */
299int tcp_set_allowed_congestion_control(char *val)
300{
301 struct tcp_congestion_ops *ca;
302 char *saved_clone, *clone, *name;
303 int ret = 0;
304
305 saved_clone = clone = kstrdup(val, GFP_USER);
306 if (!clone)
307 return -ENOMEM;
308
309 spin_lock(&tcp_cong_list_lock);
310 /* pass 1 check for bad entries */
311 while ((name = strsep(&clone, " ")) && *name) {
312 ca = tcp_ca_find(name);
313 if (!ca) {
314 ret = -ENOENT;
315 goto out;
316 }
317 }
318
319 /* pass 2 clear old values */
320 list_for_each_entry_rcu(ca, &tcp_cong_list, list)
321 ca->flags &= ~TCP_CONG_NON_RESTRICTED;
322
323 /* pass 3 mark as allowed */
324 while ((name = strsep(&val, " ")) && *name) {
325 ca = tcp_ca_find(name);
326 WARN_ON(!ca);
327 if (ca)
328 ca->flags |= TCP_CONG_NON_RESTRICTED;
329 }
330out:
331 spin_unlock(&tcp_cong_list_lock);
332 kfree(saved_clone);
333
334 return ret;
335}
336
337/* Change congestion control for socket */
338int tcp_set_congestion_control(struct sock *sk, const char *name)
339{
340 struct inet_connection_sock *icsk = inet_csk(sk);
341 const struct tcp_congestion_ops *ca;
342 int err = 0;
343
344 if (icsk->icsk_ca_dst_locked)
345 return -EPERM;
346
347 rcu_read_lock();
348 ca = __tcp_ca_find_autoload(name);
349 /* No change asking for existing value */
350 if (ca == icsk->icsk_ca_ops) {
351 icsk->icsk_ca_setsockopt = 1;
352 goto out;
353 }
354 if (!ca)
355 err = -ENOENT;
356 else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
357 ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)))
358 err = -EPERM;
359 else if (!try_module_get(ca->owner))
360 err = -EBUSY;
361 else
362 tcp_reinit_congestion_control(sk, ca);
363 out:
364 rcu_read_unlock();
365 return err;
366}
367
368/* Slow start is used when congestion window is no greater than the slow start
369 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
370 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
371 * something better;) a packet is only considered (s)acked in its entirety to
372 * defend the ACK attacks described in the RFC. Slow start processes a stretch
373 * ACK of degree N as if N acks of degree 1 are received back to back except
374 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
375 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
376 */
377u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
378{
379 u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
380
381 acked -= cwnd - tp->snd_cwnd;
382 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
383
384 return acked;
385}
386EXPORT_SYMBOL_GPL(tcp_slow_start);
387
388/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w),
389 * for every packet that was ACKed.
390 */
391void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w, u32 acked)
392{
393 /* If credits accumulated at a higher w, apply them gently now. */
394 if (tp->snd_cwnd_cnt >= w) {
395 tp->snd_cwnd_cnt = 0;
396 tp->snd_cwnd++;
397 }
398
399 tp->snd_cwnd_cnt += acked;
400 if (tp->snd_cwnd_cnt >= w) {
401 u32 delta = tp->snd_cwnd_cnt / w;
402
403 tp->snd_cwnd_cnt -= delta * w;
404 tp->snd_cwnd += delta;
405 }
406 tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
407}
408EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
409
410/*
411 * TCP Reno congestion control
412 * This is special case used for fallback as well.
413 */
414/* This is Jacobson's slow start and congestion avoidance.
415 * SIGCOMM '88, p. 328.
416 */
417void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked)
418{
419 struct tcp_sock *tp = tcp_sk(sk);
420
421 if (!tcp_is_cwnd_limited(sk))
422 return;
423
424 /* In "safe" area, increase. */
425 if (tcp_in_slow_start(tp)) {
426 acked = tcp_slow_start(tp, acked);
427 if (!acked)
428 return;
429 }
430 /* In dangerous area, increase slowly. */
431 tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
432}
433EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
434
435/* Slow start threshold is half the congestion window (min 2) */
436u32 tcp_reno_ssthresh(struct sock *sk)
437{
438 const struct tcp_sock *tp = tcp_sk(sk);
439
440 return max(tp->snd_cwnd >> 1U, 2U);
441}
442EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
443
444struct tcp_congestion_ops tcp_reno = {
445 .flags = TCP_CONG_NON_RESTRICTED,
446 .name = "reno",
447 .owner = THIS_MODULE,
448 .ssthresh = tcp_reno_ssthresh,
449 .cong_avoid = tcp_reno_cong_avoid,
450};
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
18static DEFINE_SPINLOCK(tcp_cong_list_lock);
19static LIST_HEAD(tcp_cong_list);
20
21/* Simple linear search, don't expect many entries! */
22static 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 */
38int 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}
60EXPORT_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 */
68void 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}
74EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
75
76/* Assign choice of congestion control. */
77void 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. */
101void 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 */
111int 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 */
139static int __init tcp_congestion_default(void)
140{
141 return tcp_set_default_congestion_control(CONFIG_DEFAULT_TCP_CONG);
142}
143late_initcall(tcp_congestion_default);
144
145
146/* Build string with list of available congestion control values */
147void 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 */
163void 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 */
176void 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 */
195int 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 }
226out:
227 spin_unlock(&tcp_cong_list_lock);
228 kfree(saved_clone);
229
230 return ret;
231}
232
233
234/* Change congestion control for socket */
235int 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 */
282bool 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->xmit_size_goal_segs)
294 return true;
295 return left <= tcp_max_tso_deferred_mss(tp);
296}
297EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
298
299/* Slow start is used when congestion window is no greater than the slow start
300 * threshold. We base on RFC2581 and also handle stretch ACKs properly.
301 * We do not implement RFC3465 Appropriate Byte Counting (ABC) per se but
302 * something better;) a packet is only considered (s)acked in its entirety to
303 * defend the ACK attacks described in the RFC. Slow start processes a stretch
304 * ACK of degree N as if N acks of degree 1 are received back to back except
305 * ABC caps N to 2. Slow start exits when cwnd grows over ssthresh and
306 * returns the leftover acks to adjust cwnd in congestion avoidance mode.
307 */
308int tcp_slow_start(struct tcp_sock *tp, u32 acked)
309{
310 u32 cwnd = tp->snd_cwnd + acked;
311
312 if (cwnd > tp->snd_ssthresh)
313 cwnd = tp->snd_ssthresh + 1;
314 acked -= cwnd - tp->snd_cwnd;
315 tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
316 return acked;
317}
318EXPORT_SYMBOL_GPL(tcp_slow_start);
319
320/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd (or alternative w) */
321void tcp_cong_avoid_ai(struct tcp_sock *tp, u32 w)
322{
323 if (tp->snd_cwnd_cnt >= w) {
324 if (tp->snd_cwnd < tp->snd_cwnd_clamp)
325 tp->snd_cwnd++;
326 tp->snd_cwnd_cnt = 0;
327 } else {
328 tp->snd_cwnd_cnt++;
329 }
330}
331EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
332
333/*
334 * TCP Reno congestion control
335 * This is special case used for fallback as well.
336 */
337/* This is Jacobson's slow start and congestion avoidance.
338 * SIGCOMM '88, p. 328.
339 */
340void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 acked, u32 in_flight)
341{
342 struct tcp_sock *tp = tcp_sk(sk);
343
344 if (!tcp_is_cwnd_limited(sk, in_flight))
345 return;
346
347 /* In "safe" area, increase. */
348 if (tp->snd_cwnd <= tp->snd_ssthresh)
349 tcp_slow_start(tp, acked);
350 /* In dangerous area, increase slowly. */
351 else
352 tcp_cong_avoid_ai(tp, tp->snd_cwnd);
353}
354EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
355
356/* Slow start threshold is half the congestion window (min 2) */
357u32 tcp_reno_ssthresh(struct sock *sk)
358{
359 const struct tcp_sock *tp = tcp_sk(sk);
360 return max(tp->snd_cwnd >> 1U, 2U);
361}
362EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
363
364struct tcp_congestion_ops tcp_reno = {
365 .flags = TCP_CONG_NON_RESTRICTED,
366 .name = "reno",
367 .owner = THIS_MODULE,
368 .ssthresh = tcp_reno_ssthresh,
369 .cong_avoid = tcp_reno_cong_avoid,
370};
371
372/* Initial congestion control used (until SYN)
373 * really reno under another name so we can tell difference
374 * during tcp_set_default_congestion_control
375 */
376struct tcp_congestion_ops tcp_init_congestion_ops = {
377 .name = "",
378 .owner = THIS_MODULE,
379 .ssthresh = tcp_reno_ssthresh,
380 .cong_avoid = tcp_reno_cong_avoid,
381};
382EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);