2 * Copyright (c) 2007-2008
3 * Swinburne University of Technology, Melbourne, Australia
4 * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
5 * Copyright (c) 2010 The FreeBSD Foundation
8 * This software was developed at the Centre for Advanced Internet
9 * Architectures, Swinburne University of Technology, by Lawrence Stewart and
10 * James Healy, made possible in part by a grant from the Cisco University
11 * Research Program Fund 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 H-TCP congestion control algorithm for FreeBSD,
41 * based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and
42 * Shorten. Originally released as part of the NewTCP research project at
43 * Swinburne University of Technology's Centre for Advanced Internet
44 * Architectures, Melbourne, Australia, which was made possible in part by a
45 * grant from the Cisco University Research Program Fund at Community Foundation
46 * Silicon 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_module.h>
72 /* Fixed point math shifts. */
74 #define HTCP_ALPHA_INC_SHIFT 4
76 #define HTCP_INIT_ALPHA 1
77 #define HTCP_DELTA_L hz /* 1 sec in ticks. */
78 #define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */
79 #define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */
80 #define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */
81 #define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */
83 /* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */
84 #define HTCP_RTT_REF 100
86 /* Don't trust SRTT until this many samples have been taken. */
87 #define HTCP_MIN_RTT_SAMPLES 8
90 * HTCP_CALC_ALPHA performs a fixed point math calculation to determine the
91 * value of alpha, based on the function defined in the HTCP spec.
93 * i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2
95 * "diff" is passed in to the macro as "delta - delta_l" and is expected to be
98 * The joyousnous of fixed point maths means our function implementation looks a
101 * In order to maintain some precision in the calculations, a fixed point shift
102 * HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't
103 * truncate the results too badly.
105 * The "16" value is the "1" term in the alpha function shifted up by
106 * HTCP_ALPHA_INC_SHIFT
108 * The "160" value is the "10" multiplier in the alpha function multiplied by
109 * 2^HTCP_ALPHA_INC_SHIFT
111 * Specifying these as constants reduces the computations required. After
112 * up-shifting all the terms in the function and performing the required
113 * calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to
114 * ensure it is back in the correct range.
116 * The "hz" terms are required as kernels can be configured to run with
117 * different tick timers, which we have to adjust for in the alpha calculation
118 * (which originally was defined in terms of seconds).
120 * We also have to be careful to constrain the value of diff such that it won't
121 * overflow whilst performing the calculation. The middle term i.e. (160 * diff)
122 * / hz is the limiting factor in the calculation. We must constrain diff to be
123 * less than the max size of an int divided by the constant 160 figure
124 * i.e. diff < INT_MAX / 160
126 * NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the
127 * constants used in this function!
129 #define HTCP_CALC_ALPHA(diff) \
132 ((160 * (diff)) / hz) + \
133 (((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \
134 ) >> HTCP_ALPHA_INC_SHIFT)
136 static void htcp_ack_received(struct cc_var *ccv, uint16_t type);
137 static void htcp_cb_destroy(struct cc_var *ccv);
138 static int htcp_cb_init(struct cc_var *ccv);
139 static void htcp_cong_signal(struct cc_var *ccv, uint32_t type);
140 static int htcp_mod_init(void);
141 static void htcp_post_recovery(struct cc_var *ccv);
142 static void htcp_recalc_alpha(struct cc_var *ccv);
143 static void htcp_recalc_beta(struct cc_var *ccv);
144 static void htcp_record_rtt(struct cc_var *ccv);
145 static void htcp_ssthresh_update(struct cc_var *ccv);
148 /* cwnd before entering cong recovery. */
149 unsigned long prev_cwnd;
150 /* cwnd additive increase parameter. */
152 /* cwnd multiplicative decrease parameter. */
154 /* Largest rtt seen for the flow. */
156 /* Shortest rtt seen for the flow. */
158 /* Time of last congestion event in ticks. */
162 static int htcp_rtt_ref;
164 * The maximum number of ticks the value of diff can reach in
165 * htcp_recalc_alpha() before alpha will stop increasing due to overflow.
166 * See comment above HTCP_CALC_ALPHA for more info.
168 static int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10);
170 /* Per-netstack vars. */
171 static VNET_DEFINE(u_int, htcp_adaptive_backoff) = 0;
172 static VNET_DEFINE(u_int, htcp_rtt_scaling) = 0;
173 #define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff)
174 #define V_htcp_rtt_scaling VNET(htcp_rtt_scaling)
176 static MALLOC_DEFINE(M_HTCP, "htcp data",
177 "Per connection data required for the HTCP congestion control algorithm");
179 struct cc_algo htcp_cc_algo = {
181 .ack_received = htcp_ack_received,
182 .cb_destroy = htcp_cb_destroy,
183 .cb_init = htcp_cb_init,
184 .cong_signal = htcp_cong_signal,
185 .mod_init = htcp_mod_init,
186 .post_recovery = htcp_post_recovery,
190 htcp_ack_received(struct cc_var *ccv, uint16_t type)
192 struct htcp *htcp_data;
194 htcp_data = ccv->cc_data;
195 htcp_record_rtt(ccv);
198 * Regular ACK and we're not in cong/fast recovery and we're cwnd
199 * limited and we're either not doing ABC or are slow starting or are
200 * doing ABC and we've sent a cwnd's worth of bytes.
202 if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
203 (ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
204 CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
205 (V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
206 htcp_recalc_beta(ccv);
207 htcp_recalc_alpha(ccv);
209 * Use the logic in NewReno ack_received() for slow start and
210 * for the first HTCP_DELTA_L ticks after either the flow starts
211 * or a congestion event (when alpha equals 1).
213 if (htcp_data->alpha == 1 ||
214 CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh))
215 newreno_cc_algo.ack_received(ccv, type);
217 if (V_tcp_do_rfc3465) {
218 /* Increment cwnd by alpha segments. */
219 CCV(ccv, snd_cwnd) += htcp_data->alpha *
221 ccv->flags &= ~CCF_ABC_SENTAWND;
224 * Increment cwnd by alpha/cwnd segments to
225 * approximate an increase of alpha segments
228 CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
229 HTCP_SHIFT) / (CCV(ccv, snd_cwnd) /
230 CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg))
237 htcp_cb_destroy(struct cc_var *ccv)
240 if (ccv->cc_data != NULL)
241 free(ccv->cc_data, M_HTCP);
245 htcp_cb_init(struct cc_var *ccv)
247 struct htcp *htcp_data;
249 htcp_data = malloc(sizeof(struct htcp), M_HTCP, M_NOWAIT);
251 if (htcp_data == NULL)
254 /* Init some key variables with sensible defaults. */
255 htcp_data->alpha = HTCP_INIT_ALPHA;
256 htcp_data->beta = HTCP_MINBETA;
257 htcp_data->maxrtt = TCPTV_SRTTBASE;
258 htcp_data->minrtt = TCPTV_SRTTBASE;
259 htcp_data->prev_cwnd = 0;
260 htcp_data->t_last_cong = ticks;
262 ccv->cc_data = htcp_data;
268 * Perform any necessary tasks before we enter congestion recovery.
271 htcp_cong_signal(struct cc_var *ccv, uint32_t type)
273 struct htcp *htcp_data;
277 htcp_data = ccv->cc_data;
278 cwin = CCV(ccv, snd_cwnd);
279 mss = CCV(ccv, t_maxseg);
283 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
284 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
286 * Apply hysteresis to maxrtt to ensure
287 * reductions in the RTT are reflected in our
290 htcp_data->maxrtt = (htcp_data->minrtt +
291 (htcp_data->maxrtt - htcp_data->minrtt) *
293 htcp_ssthresh_update(ccv);
294 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
295 htcp_data->t_last_cong = ticks;
296 htcp_data->prev_cwnd = cwin;
298 ENTER_RECOVERY(CCV(ccv, t_flags));
303 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
305 * Apply hysteresis to maxrtt to ensure reductions in
306 * the RTT are reflected in our measurements.
308 htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt -
309 htcp_data->minrtt) * 95) / 100;
310 htcp_ssthresh_update(ccv);
311 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
312 htcp_data->t_last_cong = ticks;
313 htcp_data->prev_cwnd = cwin;
314 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
320 * Grab the current time and record it so we know when the
321 * most recent congestion event was. Only record it when the
322 * timeout has fired more than once, as there is a reasonable
323 * chance the first one is a false alarm and may not indicate
326 if (CCV(ccv, t_rxtshift) >= 2)
327 htcp_data->t_last_cong = ticks;
328 CCV(ccv, snd_ssthresh) =
329 max((CCV(ccv, snd_max) - CCV(ccv, snd_una)) / 2 / mss, 2)
331 CCV(ccv, snd_cwnd) = mss;
340 htcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
343 * HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in
344 * units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units
347 htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000;
353 * Perform any necessary tasks before we exit congestion recovery.
356 htcp_post_recovery(struct cc_var *ccv)
359 struct htcp *htcp_data;
362 htcp_data = ccv->cc_data;
364 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
366 * If inflight data is less than ssthresh, set cwnd
367 * conservatively to avoid a burst of data, as suggested in the
368 * NewReno RFC. Otherwise, use the HTCP method.
370 * XXXLAS: Find a way to do this without needing curack
372 if (V_tcp_do_rfc6675_pipe)
373 pipe = tcp_compute_pipe(ccv->ccvc.tcp);
375 pipe = CCV(ccv, snd_max) - ccv->curack;
377 if (pipe < CCV(ccv, snd_ssthresh))
378 CCV(ccv, snd_cwnd) = pipe + CCV(ccv, t_maxseg);
380 CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
381 htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
382 >> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
387 htcp_recalc_alpha(struct cc_var *ccv)
389 struct htcp *htcp_data;
390 int alpha, diff, now;
392 htcp_data = ccv->cc_data;
396 * If ticks has wrapped around (will happen approximately once every 49
397 * days on a machine with the default kern.hz=1000) and a flow straddles
398 * the wrap point, our alpha calcs will be completely wrong. We cut our
399 * losses and restart alpha from scratch by setting t_last_cong = now -
402 * This does not deflate our cwnd at all. It simply slows the rate cwnd
403 * is growing by until alpha regains the value it held prior to taking
404 * this drastic measure.
406 if (now < htcp_data->t_last_cong)
407 htcp_data->t_last_cong = now - HTCP_DELTA_L;
409 diff = now - htcp_data->t_last_cong - HTCP_DELTA_L;
411 /* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */
412 if (diff < htcp_max_diff) {
414 * If it has been more than HTCP_DELTA_L ticks since congestion,
415 * increase alpha according to the function defined in the spec.
418 alpha = HTCP_CALC_ALPHA(diff);
421 * Adaptive backoff fairness adjustment:
422 * 2 * (1 - beta) * alpha_raw
424 if (V_htcp_adaptive_backoff)
425 alpha = max(1, (2 * ((1 << HTCP_SHIFT) -
426 htcp_data->beta) * alpha) >> HTCP_SHIFT);
429 * RTT scaling: (RTT / RTT_ref) * alpha
430 * alpha will be the raw value from HTCP_CALC_ALPHA() if
431 * adaptive backoff is off, or the adjusted value if
432 * adaptive backoff is on.
434 if (V_htcp_rtt_scaling)
435 alpha = max(1, (min(max(HTCP_MINROWE,
436 (CCV(ccv, t_srtt) << HTCP_SHIFT) /
437 htcp_rtt_ref), HTCP_MAXROWE) * alpha)
443 htcp_data->alpha = alpha;
448 htcp_recalc_beta(struct cc_var *ccv)
450 struct htcp *htcp_data;
452 htcp_data = ccv->cc_data;
455 * TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so
456 * we only calc beta if the connection's SRTT has been changed from its
457 * initial value. beta is bounded to ensure it is always between
458 * HTCP_MINBETA and HTCP_MAXBETA.
460 if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE &&
461 htcp_data->maxrtt != TCPTV_SRTTBASE)
462 htcp_data->beta = min(max(HTCP_MINBETA,
463 (htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt),
466 htcp_data->beta = HTCP_MINBETA;
470 * Record the minimum and maximum RTT seen for the connection. These are used in
471 * the calculation of beta if adaptive backoff is enabled.
474 htcp_record_rtt(struct cc_var *ccv)
476 struct htcp *htcp_data;
478 htcp_data = ccv->cc_data;
480 /* XXXLAS: Should there be some hysteresis for minrtt? */
483 * Record the current SRTT as our minrtt if it's the smallest we've seen
484 * or minrtt is currently equal to its initialised value. Ignore SRTT
485 * until a min number of samples have been taken.
487 if ((CCV(ccv, t_srtt) < htcp_data->minrtt ||
488 htcp_data->minrtt == TCPTV_SRTTBASE) &&
489 (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES))
490 htcp_data->minrtt = CCV(ccv, t_srtt);
493 * Record the current SRTT as our maxrtt if it's the largest we've
494 * seen. Ignore SRTT until a min number of samples have been taken.
496 if (CCV(ccv, t_srtt) > htcp_data->maxrtt
497 && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)
498 htcp_data->maxrtt = CCV(ccv, t_srtt);
502 * Update the ssthresh in the event of congestion.
505 htcp_ssthresh_update(struct cc_var *ccv)
507 struct htcp *htcp_data;
509 htcp_data = ccv->cc_data;
512 * On the first congestion event, set ssthresh to cwnd * 0.5, on
513 * subsequent congestion events, set it to cwnd * beta.
515 if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT)
516 CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
517 HTCP_MINBETA) >> HTCP_SHIFT;
519 htcp_recalc_beta(ccv);
520 CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
521 htcp_data->beta) >> HTCP_SHIFT;
524 /* Align ssthresh to MSS boundary */
525 CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_ssthresh) / CCV(ccv, t_maxseg))
526 * CCV(ccv, t_maxseg);
530 SYSCTL_DECL(_net_inet_tcp_cc_htcp);
531 SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW,
532 NULL, "H-TCP related settings");
533 SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff,
534 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_adaptive_backoff), 0,
535 "enable H-TCP adaptive backoff");
536 SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling,
537 CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_rtt_scaling), 0,
538 "enable H-TCP RTT scaling");
540 DECLARE_CC_MODULE(htcp, &htcp_cc_algo);