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/cc.h>
66 #include <netinet/tcp_seq.h>
67 #include <netinet/tcp_timer.h>
68 #include <netinet/tcp_var.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;
275 htcp_data = ccv->cc_data;
279 if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
280 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
282 * Apply hysteresis to maxrtt to ensure
283 * reductions in the RTT are reflected in our
286 htcp_data->maxrtt = (htcp_data->minrtt +
287 (htcp_data->maxrtt - htcp_data->minrtt) *
289 htcp_ssthresh_update(ccv);
290 htcp_data->t_last_cong = ticks;
291 htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
293 ENTER_RECOVERY(CCV(ccv, t_flags));
298 if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
300 * Apply hysteresis to maxrtt to ensure reductions in
301 * the RTT are reflected in our measurements.
303 htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt -
304 htcp_data->minrtt) * 95) / 100;
305 htcp_ssthresh_update(ccv);
306 CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
307 htcp_data->t_last_cong = ticks;
308 htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
309 ENTER_CONGRECOVERY(CCV(ccv, t_flags));
315 * Grab the current time and record it so we know when the
316 * most recent congestion event was. Only record it when the
317 * timeout has fired more than once, as there is a reasonable
318 * chance the first one is a false alarm and may not indicate
321 if (CCV(ccv, t_rxtshift) >= 2)
322 htcp_data->t_last_cong = ticks;
331 htcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
334 * HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in
335 * units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units
338 htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000;
344 * Perform any necessary tasks before we exit congestion recovery.
347 htcp_post_recovery(struct cc_var *ccv)
349 struct htcp *htcp_data;
351 htcp_data = ccv->cc_data;
353 if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
355 * If inflight data is less than ssthresh, set cwnd
356 * conservatively to avoid a burst of data, as suggested in the
357 * NewReno RFC. Otherwise, use the HTCP method.
359 * XXXLAS: Find a way to do this without needing curack
361 if (SEQ_GT(ccv->curack + CCV(ccv, snd_ssthresh),
363 CCV(ccv, snd_cwnd) = CCV(ccv, snd_max) - ccv->curack +
366 CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
367 htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
368 >> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
373 htcp_recalc_alpha(struct cc_var *ccv)
375 struct htcp *htcp_data;
376 int alpha, diff, now;
378 htcp_data = ccv->cc_data;
382 * If ticks has wrapped around (will happen approximately once every 49
383 * days on a machine with the default kern.hz=1000) and a flow straddles
384 * the wrap point, our alpha calcs will be completely wrong. We cut our
385 * losses and restart alpha from scratch by setting t_last_cong = now -
388 * This does not deflate our cwnd at all. It simply slows the rate cwnd
389 * is growing by until alpha regains the value it held prior to taking
390 * this drastic measure.
392 if (now < htcp_data->t_last_cong)
393 htcp_data->t_last_cong = now - HTCP_DELTA_L;
395 diff = now - htcp_data->t_last_cong - HTCP_DELTA_L;
397 /* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */
398 if (diff < htcp_max_diff) {
400 * If it has been more than HTCP_DELTA_L ticks since congestion,
401 * increase alpha according to the function defined in the spec.
404 alpha = HTCP_CALC_ALPHA(diff);
407 * Adaptive backoff fairness adjustment:
408 * 2 * (1 - beta) * alpha_raw
410 if (V_htcp_adaptive_backoff)
411 alpha = max(1, (2 * ((1 << HTCP_SHIFT) -
412 htcp_data->beta) * alpha) >> HTCP_SHIFT);
415 * RTT scaling: (RTT / RTT_ref) * alpha
416 * alpha will be the raw value from HTCP_CALC_ALPHA() if
417 * adaptive backoff is off, or the adjusted value if
418 * adaptive backoff is on.
420 if (V_htcp_rtt_scaling)
421 alpha = max(1, (min(max(HTCP_MINROWE,
422 (CCV(ccv, t_srtt) << HTCP_SHIFT) /
423 htcp_rtt_ref), HTCP_MAXROWE) * alpha)
429 htcp_data->alpha = alpha;
434 htcp_recalc_beta(struct cc_var *ccv)
436 struct htcp *htcp_data;
438 htcp_data = ccv->cc_data;
441 * TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so
442 * we only calc beta if the connection's SRTT has been changed from its
443 * inital value. beta is bounded to ensure it is always between
444 * HTCP_MINBETA and HTCP_MAXBETA.
446 if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE &&
447 htcp_data->maxrtt != TCPTV_SRTTBASE)
448 htcp_data->beta = min(max(HTCP_MINBETA,
449 (htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt),
452 htcp_data->beta = HTCP_MINBETA;
456 * Record the minimum and maximum RTT seen for the connection. These are used in
457 * the calculation of beta if adaptive backoff is enabled.
460 htcp_record_rtt(struct cc_var *ccv)
462 struct htcp *htcp_data;
464 htcp_data = ccv->cc_data;
466 /* XXXLAS: Should there be some hysteresis for minrtt? */
469 * Record the current SRTT as our minrtt if it's the smallest we've seen
470 * or minrtt is currently equal to its initialised value. Ignore SRTT
471 * until a min number of samples have been taken.
473 if ((CCV(ccv, t_srtt) < htcp_data->minrtt ||
474 htcp_data->minrtt == TCPTV_SRTTBASE) &&
475 (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES))
476 htcp_data->minrtt = CCV(ccv, t_srtt);
479 * Record the current SRTT as our maxrtt if it's the largest we've
480 * seen. Ignore SRTT until a min number of samples have been taken.
482 if (CCV(ccv, t_srtt) > htcp_data->maxrtt
483 && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)
484 htcp_data->maxrtt = CCV(ccv, t_srtt);
488 * Update the ssthresh in the event of congestion.
491 htcp_ssthresh_update(struct cc_var *ccv)
493 struct htcp *htcp_data;
495 htcp_data = ccv->cc_data;
498 * On the first congestion event, set ssthresh to cwnd * 0.5, on
499 * subsequent congestion events, set it to cwnd * beta.
501 if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT)
502 CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * HTCP_MINBETA)
505 htcp_recalc_beta(ccv);
506 CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * htcp_data->beta)
512 SYSCTL_DECL(_net_inet_tcp_cc_htcp);
513 SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW,
514 NULL, "H-TCP related settings");
515 SYSCTL_VNET_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff, CTLFLAG_RW,
516 &VNET_NAME(htcp_adaptive_backoff), 0, "enable H-TCP adaptive backoff");
517 SYSCTL_VNET_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling, CTLFLAG_RW,
518 &VNET_NAME(htcp_rtt_scaling), 0, "enable H-TCP RTT scaling");
520 DECLARE_CC_MODULE(htcp, &htcp_cc_algo);