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Stephen Hemmingerb87d8562005-06-23 12:27:19 -07001/*
2 * TCP Vegas congestion control
3 *
4 * This is based on the congestion detection/avoidance scheme described in
5 * Lawrence S. Brakmo and Larry L. Peterson.
6 * "TCP Vegas: End to end congestion avoidance on a global internet."
7 * IEEE Journal on Selected Areas in Communication, 13(8):1465--1480,
8 * October 1995. Available from:
9 * ftp://ftp.cs.arizona.edu/xkernel/Papers/jsac.ps
10 *
11 * See http://www.cs.arizona.edu/xkernel/ for their implementation.
12 * The main aspects that distinguish this implementation from the
13 * Arizona Vegas implementation are:
14 * o We do not change the loss detection or recovery mechanisms of
15 * Linux in any way. Linux already recovers from losses quite well,
16 * using fine-grained timers, NewReno, and FACK.
17 * o To avoid the performance penalty imposed by increasing cwnd
18 * only every-other RTT during slow start, we increase during
19 * every RTT during slow start, just like Reno.
20 * o Largely to allow continuous cwnd growth during slow start,
21 * we use the rate at which ACKs come back as the "actual"
22 * rate, rather than the rate at which data is sent.
23 * o To speed convergence to the right rate, we set the cwnd
24 * to achieve the right ("actual") rate when we exit slow start.
25 * o To filter out the noise caused by delayed ACKs, we use the
26 * minimum RTT sample observed during the last RTT to calculate
27 * the actual rate.
28 * o When the sender re-starts from idle, it waits until it has
29 * received ACKs for an entire flight of new data before making
30 * a cwnd adjustment decision. The original Vegas implementation
31 * assumed senders never went idle.
32 */
33
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070034#include <linux/mm.h>
35#include <linux/module.h>
36#include <linux/skbuff.h>
Arnaldo Carvalho de Meloa8c21902005-08-12 12:56:38 -030037#include <linux/inet_diag.h>
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070038
39#include <net/tcp.h>
40
Stephen Hemminger77522372007-04-23 22:28:23 -070041#include "tcp_vegas.h"
42
Doug Leith8d3a5642008-12-09 00:13:04 -080043static int alpha = 2;
44static int beta = 4;
45static int gamma = 1;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070046
47module_param(alpha, int, 0644);
Doug Leith8d3a5642008-12-09 00:13:04 -080048MODULE_PARM_DESC(alpha, "lower bound of packets in network");
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070049module_param(beta, int, 0644);
Doug Leith8d3a5642008-12-09 00:13:04 -080050MODULE_PARM_DESC(beta, "upper bound of packets in network");
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070051module_param(gamma, int, 0644);
52MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");
53
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070054/* There are several situations when we must "re-start" Vegas:
55 *
56 * o when a connection is established
57 * o after an RTO
58 * o after fast recovery
59 * o when we send a packet and there is no outstanding
60 * unacknowledged data (restarting an idle connection)
61 *
62 * In these circumstances we cannot do a Vegas calculation at the
63 * end of the first RTT, because any calculation we do is using
64 * stale info -- both the saved cwnd and congestion feedback are
65 * stale.
66 *
67 * Instead we must wait until the completion of an RTT during
68 * which we actually receive ACKs.
69 */
Stephen Hemminger77522372007-04-23 22:28:23 -070070static void vegas_enable(struct sock *sk)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070071{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -030072 const struct tcp_sock *tp = tcp_sk(sk);
73 struct vegas *vegas = inet_csk_ca(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070074
75 /* Begin taking Vegas samples next time we send something. */
76 vegas->doing_vegas_now = 1;
77
78 /* Set the beginning of the next send window. */
79 vegas->beg_snd_nxt = tp->snd_nxt;
80
81 vegas->cntRTT = 0;
82 vegas->minRTT = 0x7fffffff;
83}
84
85/* Stop taking Vegas samples for now. */
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -030086static inline void vegas_disable(struct sock *sk)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070087{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -030088 struct vegas *vegas = inet_csk_ca(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070089
90 vegas->doing_vegas_now = 0;
91}
92
Stephen Hemminger77522372007-04-23 22:28:23 -070093void tcp_vegas_init(struct sock *sk)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070094{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -030095 struct vegas *vegas = inet_csk_ca(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070096
97 vegas->baseRTT = 0x7fffffff;
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -030098 vegas_enable(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -070099}
Stephen Hemminger77522372007-04-23 22:28:23 -0700100EXPORT_SYMBOL_GPL(tcp_vegas_init);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700101
102/* Do RTT sampling needed for Vegas.
103 * Basically we:
104 * o min-filter RTT samples from within an RTT to get the current
105 * propagation delay + queuing delay (we are min-filtering to try to
106 * avoid the effects of delayed ACKs)
107 * o min-filter RTT samples from a much longer window (forever for now)
108 * to find the propagation delay (baseRTT)
109 */
Stephen Hemminger30cfd0b2007-07-25 23:49:34 -0700110void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700111{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300112 struct vegas *vegas = inet_csk_ca(sk);
Stephen Hemminger164891a2007-04-23 22:26:16 -0700113 u32 vrtt;
114
Stephen Hemminger30cfd0b2007-07-25 23:49:34 -0700115 if (rtt_us < 0)
Ilpo Järvinenb9ce2042007-06-15 15:08:43 -0700116 return;
117
Stephen Hemminger164891a2007-04-23 22:26:16 -0700118 /* Never allow zero rtt or baseRTT */
Stephen Hemminger30cfd0b2007-07-25 23:49:34 -0700119 vrtt = rtt_us + 1;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700120
121 /* Filter to find propagation delay: */
122 if (vrtt < vegas->baseRTT)
123 vegas->baseRTT = vrtt;
124
125 /* Find the min RTT during the last RTT to find
126 * the current prop. delay + queuing delay:
127 */
128 vegas->minRTT = min(vegas->minRTT, vrtt);
129 vegas->cntRTT++;
130}
Stephen Hemminger77522372007-04-23 22:28:23 -0700131EXPORT_SYMBOL_GPL(tcp_vegas_pkts_acked);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700132
Stephen Hemminger77522372007-04-23 22:28:23 -0700133void tcp_vegas_state(struct sock *sk, u8 ca_state)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700134{
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700135 if (ca_state == TCP_CA_Open)
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300136 vegas_enable(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700137 else
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300138 vegas_disable(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700139}
Stephen Hemminger77522372007-04-23 22:28:23 -0700140EXPORT_SYMBOL_GPL(tcp_vegas_state);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700141
142/*
143 * If the connection is idle and we are restarting,
144 * then we don't want to do any Vegas calculations
145 * until we get fresh RTT samples. So when we
146 * restart, we reset our Vegas state to a clean
147 * slate. After we get acks for this flight of
148 * packets, _then_ we can make Vegas calculations
149 * again.
150 */
Stephen Hemminger77522372007-04-23 22:28:23 -0700151void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700152{
153 if (event == CA_EVENT_CWND_RESTART ||
154 event == CA_EVENT_TX_START)
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300155 tcp_vegas_init(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700156}
Stephen Hemminger77522372007-04-23 22:28:23 -0700157EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700158
Doug Leithc80a5cd2009-05-25 22:44:59 -0700159static inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp)
160{
161 return min(tp->snd_ssthresh, tp->snd_cwnd-1);
162}
163
Eric Dumazet24901552014-05-02 21:18:05 -0700164static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 acked)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700165{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300166 struct tcp_sock *tp = tcp_sk(sk);
167 struct vegas *vegas = inet_csk_ca(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700168
Harvey Harrisonab598592008-05-01 02:47:38 -0700169 if (!vegas->doing_vegas_now) {
Eric Dumazet24901552014-05-02 21:18:05 -0700170 tcp_reno_cong_avoid(sk, ack, acked);
Harvey Harrisonab598592008-05-01 02:47:38 -0700171 return;
172 }
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700173
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700174 if (after(ack, vegas->beg_snd_nxt)) {
175 /* Do the Vegas once-per-RTT cwnd adjustment. */
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700176
177 /* Save the extent of the current window so we can use this
178 * at the end of the next RTT.
179 */
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700180 vegas->beg_snd_nxt = tp->snd_nxt;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700181
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700182 /* We do the Vegas calculations only if we got enough RTT
183 * samples that we can be reasonably sure that we got
184 * at least one RTT sample that wasn't from a delayed ACK.
185 * If we only had 2 samples total,
186 * then that means we're getting only 1 ACK per RTT, which
187 * means they're almost certainly delayed ACKs.
188 * If we have 3 samples, we should be OK.
189 */
190
191 if (vegas->cntRTT <= 2) {
192 /* We don't have enough RTT samples to do the Vegas
193 * calculation, so we'll behave like Reno.
194 */
Eric Dumazet24901552014-05-02 21:18:05 -0700195 tcp_reno_cong_avoid(sk, ack, acked);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700196 } else {
Lachlan Andrew15913112008-04-30 01:04:03 -0700197 u32 rtt, diff;
198 u64 target_cwnd;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700199
200 /* We have enough RTT samples, so, using the Vegas
201 * algorithm, we determine if we should increase or
202 * decrease cwnd, and by how much.
203 */
204
205 /* Pluck out the RTT we are using for the Vegas
206 * calculations. This is the min RTT seen during the
207 * last RTT. Taking the min filters out the effects
208 * of delayed ACKs, at the cost of noticing congestion
209 * a bit later.
210 */
211 rtt = vegas->minRTT;
212
213 /* Calculate the cwnd we should have, if we weren't
214 * going too fast.
215 *
216 * This is:
217 * (actual rate in segments) * baseRTT
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700218 */
Christoph Paasch1f74e612014-07-29 13:40:57 +0200219 target_cwnd = (u64)tp->snd_cwnd * vegas->baseRTT;
220 do_div(target_cwnd, rtt);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700221
222 /* Calculate the difference between the window we had,
223 * and the window we would like to have. This quantity
224 * is the "Diff" from the Arizona Vegas papers.
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700225 */
Doug Leith8d3a5642008-12-09 00:13:04 -0800226 diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700227
Yuchung Cheng071d5082015-07-09 13:16:29 -0700228 if (diff > gamma && tcp_in_slow_start(tp)) {
Xiaoliang (David) Weic9405872007-10-29 20:24:36 -0700229 /* Going too fast. Time to slow down
230 * and switch to congestion avoidance.
231 */
Xiaoliang (David) Weic9405872007-10-29 20:24:36 -0700232
233 /* Set cwnd to match the actual rate
234 * exactly:
235 * cwnd = (actual rate) * baseRTT
236 * Then we add 1 because the integer
237 * truncation robs us of full link
238 * utilization.
239 */
Doug Leith8d3a5642008-12-09 00:13:04 -0800240 tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
Doug Leithc80a5cd2009-05-25 22:44:59 -0700241 tp->snd_ssthresh = tcp_vegas_ssthresh(tp);
Xiaoliang (David) Weic9405872007-10-29 20:24:36 -0700242
Yuchung Cheng071d5082015-07-09 13:16:29 -0700243 } else if (tcp_in_slow_start(tp)) {
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700244 /* Slow start. */
Yuchung Cheng9f9843a72013-10-31 11:07:31 -0700245 tcp_slow_start(tp, acked);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700246 } else {
247 /* Congestion avoidance. */
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700248
249 /* Figure out where we would like cwnd
250 * to be.
251 */
252 if (diff > beta) {
253 /* The old window was too fast, so
254 * we slow down.
255 */
Doug Leith8d3a5642008-12-09 00:13:04 -0800256 tp->snd_cwnd--;
Doug Leithc80a5cd2009-05-25 22:44:59 -0700257 tp->snd_ssthresh
258 = tcp_vegas_ssthresh(tp);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700259 } else if (diff < alpha) {
260 /* We don't have enough extra packets
261 * in the network, so speed up.
262 */
Doug Leith8d3a5642008-12-09 00:13:04 -0800263 tp->snd_cwnd++;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700264 } else {
265 /* Sending just as fast as we
266 * should be.
267 */
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700268 }
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700269 }
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700270
Stephen Hemminger7faffa12005-11-10 17:07:24 -0800271 if (tp->snd_cwnd < 2)
272 tp->snd_cwnd = 2;
273 else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
274 tp->snd_cwnd = tp->snd_cwnd_clamp;
Doug Leitha6af2d62008-12-04 17:17:18 -0800275
276 tp->snd_ssthresh = tcp_current_ssthresh(sk);
Stephen Hemminger7faffa12005-11-10 17:07:24 -0800277 }
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700278
Thomas Young5b495612005-12-06 16:16:34 -0800279 /* Wipe the slate clean for the next RTT. */
280 vegas->cntRTT = 0;
281 vegas->minRTT = 0x7fffffff;
282 }
Thomas Young74cb8792006-01-04 13:59:32 -0800283 /* Use normal slow start */
Yuchung Cheng071d5082015-07-09 13:16:29 -0700284 else if (tcp_in_slow_start(tp))
Yuchung Cheng9f9843a72013-10-31 11:07:31 -0700285 tcp_slow_start(tp, acked);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700286}
287
288/* Extract info for Tcp socket info provided via netlink. */
Eric Dumazet64f40ff2015-04-28 16:23:48 -0700289size_t tcp_vegas_get_info(struct sock *sk, u32 ext, int *attr,
290 union tcp_cc_info *info)
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700291{
Arnaldo Carvalho de Melo6687e982005-08-10 04:03:31 -0300292 const struct vegas *ca = inet_csk_ca(sk);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700293
Eric Dumazet64f40ff2015-04-28 16:23:48 -0700294 if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
295 info->vegas.tcpv_enabled = ca->doing_vegas_now,
296 info->vegas.tcpv_rttcnt = ca->cntRTT,
297 info->vegas.tcpv_rtt = ca->baseRTT,
298 info->vegas.tcpv_minrtt = ca->minRTT,
299
300 *attr = INET_DIAG_VEGASINFO;
301 return sizeof(struct tcpvegas_info);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700302 }
Eric Dumazet521f1cf2015-04-16 18:10:35 -0700303 return 0;
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700304}
Stephen Hemminger77522372007-04-23 22:28:23 -0700305EXPORT_SYMBOL_GPL(tcp_vegas_get_info);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700306
Stephen Hemmingera252beb2011-03-10 00:40:17 -0800307static struct tcp_congestion_ops tcp_vegas __read_mostly = {
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700308 .init = tcp_vegas_init,
309 .ssthresh = tcp_reno_ssthresh,
310 .cong_avoid = tcp_vegas_cong_avoid,
Stephen Hemminger164891a2007-04-23 22:26:16 -0700311 .pkts_acked = tcp_vegas_pkts_acked,
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700312 .set_state = tcp_vegas_state,
313 .cwnd_event = tcp_vegas_cwnd_event,
314 .get_info = tcp_vegas_get_info,
315
316 .owner = THIS_MODULE,
317 .name = "vegas",
318};
319
320static int __init tcp_vegas_register(void)
321{
Alexey Dobriyan74975d42006-08-25 17:10:33 -0700322 BUILD_BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE);
Stephen Hemmingerb87d8562005-06-23 12:27:19 -0700323 tcp_register_congestion_control(&tcp_vegas);
324 return 0;
325}
326
327static void __exit tcp_vegas_unregister(void)
328{
329 tcp_unregister_congestion_control(&tcp_vegas);
330}
331
332module_init(tcp_vegas_register);
333module_exit(tcp_vegas_unregister);
334
335MODULE_AUTHOR("Stephen Hemminger");
336MODULE_LICENSE("GPL");
337MODULE_DESCRIPTION("TCP Vegas");