2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
5 * Copyright (c) 2010 The FreeBSD Foundation
8 * This software was developed by Lawrence Stewart while studying at the Centre
9 * for Advanced Internet Architectures, Swinburne University of Technology, made
10 * possible in part by a grant from the Cisco University Research Program Fund
11 * at Community Foundation Silicon Valley.
13 * Portions of this software were developed at the Centre for Advanced
14 * Internet Architectures, Swinburne University of Technology, Melbourne,
15 * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
17 * Redistribution and use in source and binary forms, with or without
18 * modification, are permitted provided that the following conditions
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
22 * 2. Redistributions in binary form must reproduce the above copyright
23 * notice, this list of conditions and the following disclaimer in the
24 * documentation and/or other materials provided with the distribution.
26 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
29 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
40 * An implementation of the CUBIC congestion control algorithm for FreeBSD,
41 * based on the Internet Draft "draft-rhee-tcpm-cubic-02" by Rhee, Xu and Ha.
42 * Originally released as part of the NewTCP research project at Swinburne
43 * University of Technology's Centre for Advanced Internet Architectures,
44 * Melbourne, Australia, which was made possible in part by a grant from the
45 * Cisco University Research Program Fund at Community Foundation Silicon
46 * Valley. More details are available at:
47 * http://caia.swin.edu.au/urp/newtcp/
50 #include <sys/cdefs.h>
51 __FBSDID("$FreeBSD$");
53 #include <sys/param.h>
54 #include <sys/kernel.h>
55 #include <sys/limits.h>
56 #include <sys/malloc.h>
57 #include <sys/module.h>
58 #include <sys/socket.h>
59 #include <sys/socketvar.h>
60 #include <sys/sysctl.h>
61 #include <sys/systm.h>
65 #include <netinet/tcp.h>
66 #include <netinet/tcp_seq.h>
67 #include <netinet/tcp_timer.h>
68 #include <netinet/tcp_var.h>
69 #include <netinet/cc/cc.h>
70 #include <netinet/cc/cc_cubic.h>
71 #include <netinet/cc/cc_module.h>
73 static void cubic_ack_received(struct cc_var *ccv, uint16_t type);
74 static void cubic_cb_destroy(struct cc_var *ccv);
75 static int cubic_cb_init(struct cc_var *ccv);
76 static void cubic_cong_signal(struct cc_var *ccv, uint32_t type);
77 static void cubic_conn_init(struct cc_var *ccv);
78 static int cubic_mod_init(void);
79 static void cubic_post_recovery(struct cc_var *ccv);
80 static void cubic_record_rtt(struct cc_var *ccv);
81 static void cubic_ssthresh_update(struct cc_var *ccv);
82 static void cubic_after_idle(struct cc_var *ccv);
85 /* Cubic K in fixed point form with CUBIC_SHIFT worth of precision. */
87 /* Sum of RTT samples across an epoch in ticks. */
88 int64_t sum_rtt_ticks;
89 /* cwnd at the most recent congestion event. */
90 unsigned long max_cwnd;
91 /* cwnd at the previous congestion event. */
92 unsigned long prev_max_cwnd;
93 /* Number of congestion events. */
94 uint32_t num_cong_events;
95 /* Minimum observed rtt in ticks. */
97 /* Mean observed rtt between congestion epochs. */
99 /* ACKs since last congestion event. */
101 /* Time of last congestion event in ticks. */
105 static MALLOC_DEFINE(M_CUBIC, "cubic data",
106 "Per connection data required for the CUBIC congestion control algorithm");
108 struct cc_algo cubic_cc_algo = {
110 .ack_received = cubic_ack_received,
111 .cb_destroy = cubic_cb_destroy,
112 .cb_init = cubic_cb_init,
113 .cong_signal = cubic_cong_signal,
114 .conn_init = cubic_conn_init,
115 .mod_init = cubic_mod_init,
116 .post_recovery = cubic_post_recovery,
117 .after_idle = cubic_after_idle,
121 cubic_ack_received(struct cc_var *ccv, uint16_t type)
123 struct cubic *cubic_data;
124 unsigned long w_tf, w_cubic_next;
125 int ticks_since_cong;
127 cubic_data = ccv->cc_data;
128 cubic_record_rtt(ccv);
131 * Regular ACK and we're not in cong/fast recovery and we're cwnd
132 * limited and we're either not doing ABC or are slow starting or are
133 * doing ABC and we've sent a cwnd's worth of bytes.
135 if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
136 (ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
137 CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
138 (V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
139 /* Use the logic in NewReno ack_received() for slow start. */
140 if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
141 cubic_data->min_rtt_ticks == TCPTV_SRTTBASE)
142 newreno_cc_algo.ack_received(ccv, type);
144 if ((ticks_since_cong =
145 ticks - cubic_data->t_last_cong) < 0) {
147 * dragging t_last_cong along
149 ticks_since_cong = INT_MAX;
150 cubic_data->t_last_cong = ticks - INT_MAX;
154 * The mean RTT is used to best reflect the equations in
155 * the I-D. Using min_rtt in the tf_cwnd calculation
156 * causes w_tf to grow much faster than it should if the
157 * RTT is dominated by network buffering rather than
160 w_tf = tf_cwnd(ticks_since_cong,
161 cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
164 w_cubic_next = cubic_cwnd(ticks_since_cong +
165 cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
166 CCV(ccv, t_maxseg), cubic_data->K);
168 ccv->flags &= ~CCF_ABC_SENTAWND;
170 if (w_cubic_next < w_tf) {
172 * TCP-friendly region, follow tf
175 if (CCV(ccv, snd_cwnd) < w_tf)
176 CCV(ccv, snd_cwnd) = ulmin(w_tf, INT_MAX);
179 else if (CCV(ccv, snd_cwnd) < w_cubic_next) {
181 * Concave or convex region, follow CUBIC
184 if (V_tcp_do_rfc3465)
185 CCV(ccv, snd_cwnd) = ulmin(w_cubic_next,
188 CCV(ccv, snd_cwnd) += ulmax(1,
189 ((ulmin(w_cubic_next, INT_MAX) -
190 CCV(ccv, snd_cwnd)) *
191 CCV(ccv, t_maxseg)) /
196 * If we're not in slow start and we're probing for a
197 * new cwnd limit at the start of a connection
198 * (happens when hostcache has a relevant entry),
199 * keep updating our current estimate of the
202 if (cubic_data->num_cong_events == 0 &&
203 cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) {
204 cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
205 cubic_data->K = cubic_k(cubic_data->max_cwnd /
213 * This is a Cubic specific implementation of after_idle.
214 * - Reset cwnd by calling New Reno implementation of after_idle.
215 * - Reset t_last_cong.
218 cubic_after_idle(struct cc_var *ccv)
220 struct cubic *cubic_data;
222 cubic_data = ccv->cc_data;
224 cubic_data->max_cwnd = ulmax(cubic_data->max_cwnd, CCV(ccv, snd_cwnd));
225 cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
227 newreno_cc_algo.after_idle(ccv);
228 cubic_data->t_last_cong = ticks;
233 cubic_cb_destroy(struct cc_var *ccv)
235 free(ccv->cc_data, M_CUBIC);
239 cubic_cb_init(struct cc_var *ccv)
241 struct cubic *cubic_data;
243 cubic_data = malloc(sizeof(struct cubic), M_CUBIC, M_NOWAIT|M_ZERO);
245 if (cubic_data == NULL)
248 /* Init some key variables with sensible defaults. */
249 cubic_data->t_last_cong = ticks;
250 cubic_data->min_rtt_ticks = TCPTV_SRTTBASE;
251 cubic_data->mean_rtt_ticks = 1;
253 ccv->cc_data = cubic_data;
259 * Perform any necessary tasks before we enter congestion recovery.
262 cubic_cong_signal(struct cc_var *ccv, uint32_t type)
264 struct cubic *cubic_data;
266 cubic_data = ccv->cc_data;
270 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
271 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
272 cubic_ssthresh_update(ccv);
273 cubic_data->num_cong_events++;
274 cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
275 cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
277 ENTER_RECOVERY(CCV(ccv, t_flags));
282 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
283 cubic_ssthresh_update(ccv);
284 cubic_data->num_cong_events++;
285 cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
286 cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
287 cubic_data->t_last_cong = ticks;
288 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
289 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
295 * Grab the current time and record it so we know when the
296 * most recent congestion event was. Only record it when the
297 * timeout has fired more than once, as there is a reasonable
298 * chance the first one is a false alarm and may not indicate
301 if (CCV(ccv, t_rxtshift) >= 2) {
302 cubic_data->num_cong_events++;
303 cubic_data->t_last_cong = ticks;
310 cubic_conn_init(struct cc_var *ccv)
312 struct cubic *cubic_data;
314 cubic_data = ccv->cc_data;
317 * Ensure we have a sane initial value for max_cwnd recorded. Without
318 * this here bad things happen when entries from the TCP hostcache
321 cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
331 * Perform any necessary tasks before we exit congestion recovery.
334 cubic_post_recovery(struct cc_var *ccv)
336 struct cubic *cubic_data;
339 cubic_data = ccv->cc_data;
342 /* Fast convergence heuristic. */
343 if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd)
344 cubic_data->max_cwnd = (cubic_data->max_cwnd * CUBIC_FC_FACTOR)
347 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
349 * If inflight data is less than ssthresh, set cwnd
350 * conservatively to avoid a burst of data, as suggested in
351 * the NewReno RFC. Otherwise, use the CUBIC method.
353 * XXXLAS: Find a way to do this without needing curack
355 if (V_tcp_do_rfc6675_pipe)
356 pipe = tcp_compute_pipe(ccv->ccvc.tcp);
358 pipe = CCV(ccv, snd_max) - ccv->curack;
360 if (pipe < CCV(ccv, snd_ssthresh))
362 * Ensure that cwnd does not collapse to 1 MSS under
363 * adverse conditions. Implements RFC6582
365 CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
368 /* Update cwnd based on beta and adjusted max_cwnd. */
369 CCV(ccv, snd_cwnd) = max(1, ((CUBIC_BETA *
370 cubic_data->max_cwnd) >> CUBIC_SHIFT));
372 cubic_data->t_last_cong = ticks;
374 /* Calculate the average RTT between congestion epochs. */
375 if (cubic_data->epoch_ack_count > 0 &&
376 cubic_data->sum_rtt_ticks >= cubic_data->epoch_ack_count) {
377 cubic_data->mean_rtt_ticks = (int)(cubic_data->sum_rtt_ticks /
378 cubic_data->epoch_ack_count);
381 cubic_data->epoch_ack_count = 0;
382 cubic_data->sum_rtt_ticks = 0;
383 cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
387 * Record the min RTT and sum samples for the epoch average RTT calculation.
390 cubic_record_rtt(struct cc_var *ccv)
392 struct cubic *cubic_data;
395 /* Ignore srtt until a min number of samples have been taken. */
396 if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) {
397 cubic_data = ccv->cc_data;
398 t_srtt_ticks = CCV(ccv, t_srtt) / TCP_RTT_SCALE;
401 * Record the current SRTT as our minrtt if it's the smallest
402 * we've seen or minrtt is currently equal to its initialised
405 * XXXLAS: Should there be some hysteresis for minrtt?
407 if ((t_srtt_ticks < cubic_data->min_rtt_ticks ||
408 cubic_data->min_rtt_ticks == TCPTV_SRTTBASE)) {
409 cubic_data->min_rtt_ticks = max(1, t_srtt_ticks);
412 * If the connection is within its first congestion
413 * epoch, ensure we prime mean_rtt_ticks with a
414 * reasonable value until the epoch average RTT is
415 * calculated in cubic_post_recovery().
417 if (cubic_data->min_rtt_ticks >
418 cubic_data->mean_rtt_ticks)
419 cubic_data->mean_rtt_ticks =
420 cubic_data->min_rtt_ticks;
423 /* Sum samples for epoch average RTT calculation. */
424 cubic_data->sum_rtt_ticks += t_srtt_ticks;
425 cubic_data->epoch_ack_count++;
430 * Update the ssthresh in the event of congestion.
433 cubic_ssthresh_update(struct cc_var *ccv)
435 struct cubic *cubic_data;
437 cubic_data = ccv->cc_data;
440 * On the first congestion event, set ssthresh to cwnd * 0.5, on
441 * subsequent congestion events, set it to cwnd * beta.
443 if (cubic_data->num_cong_events == 0)
444 CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd) >> 1;
446 CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
447 CUBIC_BETA) >> CUBIC_SHIFT;
451 DECLARE_CC_MODULE(cubic, &cubic_cc_algo);