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Commit | Line | Data |
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b87d8561 SH |
1 | /* |
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 | ||
b87d8561 SH |
34 | #include <linux/mm.h> |
35 | #include <linux/module.h> | |
36 | #include <linux/skbuff.h> | |
a8c2190e | 37 | #include <linux/inet_diag.h> |
b87d8561 SH |
38 | |
39 | #include <net/tcp.h> | |
40 | ||
7752237e SH |
41 | #include "tcp_vegas.h" |
42 | ||
b87d8561 SH |
43 | /* Default values of the Vegas variables, in fixed-point representation |
44 | * with V_PARAM_SHIFT bits to the right of the binary point. | |
45 | */ | |
46 | #define V_PARAM_SHIFT 1 | |
d2e4bdc8 DM |
47 | static int alpha = 2<<V_PARAM_SHIFT; |
48 | static int beta = 4<<V_PARAM_SHIFT; | |
b87d8561 SH |
49 | static int gamma = 1<<V_PARAM_SHIFT; |
50 | ||
51 | module_param(alpha, int, 0644); | |
52 | MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)"); | |
53 | module_param(beta, int, 0644); | |
54 | MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)"); | |
55 | module_param(gamma, int, 0644); | |
56 | MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)"); | |
57 | ||
58 | ||
b87d8561 SH |
59 | /* There are several situations when we must "re-start" Vegas: |
60 | * | |
61 | * o when a connection is established | |
62 | * o after an RTO | |
63 | * o after fast recovery | |
64 | * o when we send a packet and there is no outstanding | |
65 | * unacknowledged data (restarting an idle connection) | |
66 | * | |
67 | * In these circumstances we cannot do a Vegas calculation at the | |
68 | * end of the first RTT, because any calculation we do is using | |
69 | * stale info -- both the saved cwnd and congestion feedback are | |
70 | * stale. | |
71 | * | |
72 | * Instead we must wait until the completion of an RTT during | |
73 | * which we actually receive ACKs. | |
74 | */ | |
7752237e | 75 | static void vegas_enable(struct sock *sk) |
b87d8561 | 76 | { |
6687e988 ACM |
77 | const struct tcp_sock *tp = tcp_sk(sk); |
78 | struct vegas *vegas = inet_csk_ca(sk); | |
b87d8561 SH |
79 | |
80 | /* Begin taking Vegas samples next time we send something. */ | |
81 | vegas->doing_vegas_now = 1; | |
82 | ||
83 | /* Set the beginning of the next send window. */ | |
84 | vegas->beg_snd_nxt = tp->snd_nxt; | |
85 | ||
86 | vegas->cntRTT = 0; | |
87 | vegas->minRTT = 0x7fffffff; | |
88 | } | |
89 | ||
90 | /* Stop taking Vegas samples for now. */ | |
6687e988 | 91 | static inline void vegas_disable(struct sock *sk) |
b87d8561 | 92 | { |
6687e988 | 93 | struct vegas *vegas = inet_csk_ca(sk); |
b87d8561 SH |
94 | |
95 | vegas->doing_vegas_now = 0; | |
96 | } | |
97 | ||
7752237e | 98 | void tcp_vegas_init(struct sock *sk) |
b87d8561 | 99 | { |
6687e988 | 100 | struct vegas *vegas = inet_csk_ca(sk); |
b87d8561 SH |
101 | |
102 | vegas->baseRTT = 0x7fffffff; | |
6687e988 | 103 | vegas_enable(sk); |
b87d8561 | 104 | } |
7752237e | 105 | EXPORT_SYMBOL_GPL(tcp_vegas_init); |
b87d8561 SH |
106 | |
107 | /* Do RTT sampling needed for Vegas. | |
108 | * Basically we: | |
109 | * o min-filter RTT samples from within an RTT to get the current | |
110 | * propagation delay + queuing delay (we are min-filtering to try to | |
111 | * avoid the effects of delayed ACKs) | |
112 | * o min-filter RTT samples from a much longer window (forever for now) | |
113 | * to find the propagation delay (baseRTT) | |
114 | */ | |
30cfd0ba | 115 | void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, s32 rtt_us) |
b87d8561 | 116 | { |
6687e988 | 117 | struct vegas *vegas = inet_csk_ca(sk); |
164891aa SH |
118 | u32 vrtt; |
119 | ||
30cfd0ba | 120 | if (rtt_us < 0) |
b9ce204f IJ |
121 | return; |
122 | ||
164891aa | 123 | /* Never allow zero rtt or baseRTT */ |
30cfd0ba | 124 | vrtt = rtt_us + 1; |
b87d8561 SH |
125 | |
126 | /* Filter to find propagation delay: */ | |
127 | if (vrtt < vegas->baseRTT) | |
128 | vegas->baseRTT = vrtt; | |
129 | ||
130 | /* Find the min RTT during the last RTT to find | |
131 | * the current prop. delay + queuing delay: | |
132 | */ | |
133 | vegas->minRTT = min(vegas->minRTT, vrtt); | |
134 | vegas->cntRTT++; | |
135 | } | |
7752237e | 136 | EXPORT_SYMBOL_GPL(tcp_vegas_pkts_acked); |
b87d8561 | 137 | |
7752237e | 138 | void tcp_vegas_state(struct sock *sk, u8 ca_state) |
b87d8561 SH |
139 | { |
140 | ||
141 | if (ca_state == TCP_CA_Open) | |
6687e988 | 142 | vegas_enable(sk); |
b87d8561 | 143 | else |
6687e988 | 144 | vegas_disable(sk); |
b87d8561 | 145 | } |
7752237e | 146 | EXPORT_SYMBOL_GPL(tcp_vegas_state); |
b87d8561 SH |
147 | |
148 | /* | |
149 | * If the connection is idle and we are restarting, | |
150 | * then we don't want to do any Vegas calculations | |
151 | * until we get fresh RTT samples. So when we | |
152 | * restart, we reset our Vegas state to a clean | |
153 | * slate. After we get acks for this flight of | |
154 | * packets, _then_ we can make Vegas calculations | |
155 | * again. | |
156 | */ | |
7752237e | 157 | void tcp_vegas_cwnd_event(struct sock *sk, enum tcp_ca_event event) |
b87d8561 SH |
158 | { |
159 | if (event == CA_EVENT_CWND_RESTART || | |
160 | event == CA_EVENT_TX_START) | |
6687e988 | 161 | tcp_vegas_init(sk); |
b87d8561 | 162 | } |
7752237e | 163 | EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event); |
b87d8561 | 164 | |
c3a05c60 | 165 | static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight) |
b87d8561 | 166 | { |
6687e988 ACM |
167 | struct tcp_sock *tp = tcp_sk(sk); |
168 | struct vegas *vegas = inet_csk_ca(sk); | |
b87d8561 SH |
169 | |
170 | if (!vegas->doing_vegas_now) | |
c3a05c60 | 171 | return tcp_reno_cong_avoid(sk, ack, in_flight); |
b87d8561 SH |
172 | |
173 | /* The key players are v_beg_snd_una and v_beg_snd_nxt. | |
174 | * | |
175 | * These are so named because they represent the approximate values | |
176 | * of snd_una and snd_nxt at the beginning of the current RTT. More | |
177 | * precisely, they represent the amount of data sent during the RTT. | |
178 | * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt, | |
179 | * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding | |
180 | * bytes of data have been ACKed during the course of the RTT, giving | |
181 | * an "actual" rate of: | |
182 | * | |
183 | * (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration) | |
184 | * | |
185 | * Unfortunately, v_beg_snd_una is not exactly equal to snd_una, | |
186 | * because delayed ACKs can cover more than one segment, so they | |
187 | * don't line up nicely with the boundaries of RTTs. | |
188 | * | |
189 | * Another unfortunate fact of life is that delayed ACKs delay the | |
190 | * advance of the left edge of our send window, so that the number | |
191 | * of bytes we send in an RTT is often less than our cwnd will allow. | |
192 | * So we keep track of our cwnd separately, in v_beg_snd_cwnd. | |
193 | */ | |
194 | ||
195 | if (after(ack, vegas->beg_snd_nxt)) { | |
196 | /* Do the Vegas once-per-RTT cwnd adjustment. */ | |
197 | u32 old_wnd, old_snd_cwnd; | |
198 | ||
199 | ||
200 | /* Here old_wnd is essentially the window of data that was | |
201 | * sent during the previous RTT, and has all | |
202 | * been acknowledged in the course of the RTT that ended | |
203 | * with the ACK we just received. Likewise, old_snd_cwnd | |
204 | * is the cwnd during the previous RTT. | |
205 | */ | |
206 | old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) / | |
207 | tp->mss_cache; | |
208 | old_snd_cwnd = vegas->beg_snd_cwnd; | |
209 | ||
210 | /* Save the extent of the current window so we can use this | |
211 | * at the end of the next RTT. | |
212 | */ | |
213 | vegas->beg_snd_una = vegas->beg_snd_nxt; | |
214 | vegas->beg_snd_nxt = tp->snd_nxt; | |
215 | vegas->beg_snd_cwnd = tp->snd_cwnd; | |
216 | ||
b87d8561 SH |
217 | /* We do the Vegas calculations only if we got enough RTT |
218 | * samples that we can be reasonably sure that we got | |
219 | * at least one RTT sample that wasn't from a delayed ACK. | |
220 | * If we only had 2 samples total, | |
221 | * then that means we're getting only 1 ACK per RTT, which | |
222 | * means they're almost certainly delayed ACKs. | |
223 | * If we have 3 samples, we should be OK. | |
224 | */ | |
225 | ||
226 | if (vegas->cntRTT <= 2) { | |
227 | /* We don't have enough RTT samples to do the Vegas | |
228 | * calculation, so we'll behave like Reno. | |
229 | */ | |
c3a05c60 | 230 | tcp_reno_cong_avoid(sk, ack, in_flight); |
b87d8561 SH |
231 | } else { |
232 | u32 rtt, target_cwnd, diff; | |
233 | ||
234 | /* We have enough RTT samples, so, using the Vegas | |
235 | * algorithm, we determine if we should increase or | |
236 | * decrease cwnd, and by how much. | |
237 | */ | |
238 | ||
239 | /* Pluck out the RTT we are using for the Vegas | |
240 | * calculations. This is the min RTT seen during the | |
241 | * last RTT. Taking the min filters out the effects | |
242 | * of delayed ACKs, at the cost of noticing congestion | |
243 | * a bit later. | |
244 | */ | |
245 | rtt = vegas->minRTT; | |
246 | ||
247 | /* Calculate the cwnd we should have, if we weren't | |
248 | * going too fast. | |
249 | * | |
250 | * This is: | |
251 | * (actual rate in segments) * baseRTT | |
252 | * We keep it as a fixed point number with | |
253 | * V_PARAM_SHIFT bits to the right of the binary point. | |
254 | */ | |
255 | target_cwnd = ((old_wnd * vegas->baseRTT) | |
256 | << V_PARAM_SHIFT) / rtt; | |
257 | ||
258 | /* Calculate the difference between the window we had, | |
259 | * and the window we would like to have. This quantity | |
260 | * is the "Diff" from the Arizona Vegas papers. | |
261 | * | |
262 | * Again, this is a fixed point number with | |
263 | * V_PARAM_SHIFT bits to the right of the binary | |
264 | * point. | |
265 | */ | |
266 | diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd; | |
267 | ||
c940587b XDW |
268 | if (diff > gamma && tp->snd_ssthresh > 2 ) { |
269 | /* Going too fast. Time to slow down | |
270 | * and switch to congestion avoidance. | |
271 | */ | |
272 | tp->snd_ssthresh = 2; | |
273 | ||
274 | /* Set cwnd to match the actual rate | |
275 | * exactly: | |
276 | * cwnd = (actual rate) * baseRTT | |
277 | * Then we add 1 because the integer | |
278 | * truncation robs us of full link | |
279 | * utilization. | |
280 | */ | |
281 | tp->snd_cwnd = min(tp->snd_cwnd, | |
282 | (target_cwnd >> | |
283 | V_PARAM_SHIFT)+1); | |
b87d8561 | 284 | |
c940587b XDW |
285 | } else if (tp->snd_cwnd <= tp->snd_ssthresh) { |
286 | /* Slow start. */ | |
7faffa1c | 287 | tcp_slow_start(tp); |
b87d8561 SH |
288 | } else { |
289 | /* Congestion avoidance. */ | |
290 | u32 next_snd_cwnd; | |
291 | ||
292 | /* Figure out where we would like cwnd | |
293 | * to be. | |
294 | */ | |
295 | if (diff > beta) { | |
296 | /* The old window was too fast, so | |
297 | * we slow down. | |
298 | */ | |
299 | next_snd_cwnd = old_snd_cwnd - 1; | |
300 | } else if (diff < alpha) { | |
301 | /* We don't have enough extra packets | |
302 | * in the network, so speed up. | |
303 | */ | |
304 | next_snd_cwnd = old_snd_cwnd + 1; | |
305 | } else { | |
306 | /* Sending just as fast as we | |
307 | * should be. | |
308 | */ | |
309 | next_snd_cwnd = old_snd_cwnd; | |
310 | } | |
311 | ||
312 | /* Adjust cwnd upward or downward, toward the | |
313 | * desired value. | |
314 | */ | |
315 | if (next_snd_cwnd > tp->snd_cwnd) | |
316 | tp->snd_cwnd++; | |
317 | else if (next_snd_cwnd < tp->snd_cwnd) | |
318 | tp->snd_cwnd--; | |
319 | } | |
b87d8561 | 320 | |
7faffa1c SH |
321 | if (tp->snd_cwnd < 2) |
322 | tp->snd_cwnd = 2; | |
323 | else if (tp->snd_cwnd > tp->snd_cwnd_clamp) | |
324 | tp->snd_cwnd = tp->snd_cwnd_clamp; | |
325 | } | |
b87d8561 | 326 | |
5b495613 TY |
327 | /* Wipe the slate clean for the next RTT. */ |
328 | vegas->cntRTT = 0; | |
329 | vegas->minRTT = 0x7fffffff; | |
330 | } | |
74cb8798 | 331 | /* Use normal slow start */ |
e905a9ed | 332 | else if (tp->snd_cwnd <= tp->snd_ssthresh) |
74cb8798 | 333 | tcp_slow_start(tp); |
e905a9ed | 334 | |
b87d8561 SH |
335 | } |
336 | ||
337 | /* Extract info for Tcp socket info provided via netlink. */ | |
7752237e | 338 | void tcp_vegas_get_info(struct sock *sk, u32 ext, struct sk_buff *skb) |
b87d8561 | 339 | { |
6687e988 | 340 | const struct vegas *ca = inet_csk_ca(sk); |
73c1f4a0 | 341 | if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) { |
e9195d67 TG |
342 | struct tcpvegas_info info = { |
343 | .tcpv_enabled = ca->doing_vegas_now, | |
344 | .tcpv_rttcnt = ca->cntRTT, | |
345 | .tcpv_rtt = ca->baseRTT, | |
346 | .tcpv_minrtt = ca->minRTT, | |
347 | }; | |
348 | ||
349 | nla_put(skb, INET_DIAG_VEGASINFO, sizeof(info), &info); | |
b87d8561 SH |
350 | } |
351 | } | |
7752237e | 352 | EXPORT_SYMBOL_GPL(tcp_vegas_get_info); |
b87d8561 SH |
353 | |
354 | static struct tcp_congestion_ops tcp_vegas = { | |
164891aa | 355 | .flags = TCP_CONG_RTT_STAMP, |
b87d8561 SH |
356 | .init = tcp_vegas_init, |
357 | .ssthresh = tcp_reno_ssthresh, | |
358 | .cong_avoid = tcp_vegas_cong_avoid, | |
359 | .min_cwnd = tcp_reno_min_cwnd, | |
164891aa | 360 | .pkts_acked = tcp_vegas_pkts_acked, |
b87d8561 SH |
361 | .set_state = tcp_vegas_state, |
362 | .cwnd_event = tcp_vegas_cwnd_event, | |
363 | .get_info = tcp_vegas_get_info, | |
364 | ||
365 | .owner = THIS_MODULE, | |
366 | .name = "vegas", | |
367 | }; | |
368 | ||
369 | static int __init tcp_vegas_register(void) | |
370 | { | |
74975d40 | 371 | BUILD_BUG_ON(sizeof(struct vegas) > ICSK_CA_PRIV_SIZE); |
b87d8561 SH |
372 | tcp_register_congestion_control(&tcp_vegas); |
373 | return 0; | |
374 | } | |
375 | ||
376 | static void __exit tcp_vegas_unregister(void) | |
377 | { | |
378 | tcp_unregister_congestion_control(&tcp_vegas); | |
379 | } | |
380 | ||
381 | module_init(tcp_vegas_register); | |
382 | module_exit(tcp_vegas_unregister); | |
383 | ||
384 | MODULE_AUTHOR("Stephen Hemminger"); | |
385 | MODULE_LICENSE("GPL"); | |
386 | MODULE_DESCRIPTION("TCP Vegas"); |