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- /*-
- * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
- *
- * Copyright (c) 2007-2008
- * Swinburne University of Technology, Melbourne, Australia
- * Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
- * Copyright (c) 2010 The FreeBSD Foundation
- * All rights reserved.
- *
- * This software was developed at the Centre for Advanced Internet
- * Architectures, Swinburne University of Technology, by Lawrence Stewart and
- * James Healy, made possible in part by a grant from the Cisco University
- * Research Program Fund at Community Foundation Silicon Valley.
- *
- * Portions of this software were developed at the Centre for Advanced
- * Internet Architectures, Swinburne University of Technology, Melbourne,
- * Australia by David Hayes under sponsorship from the FreeBSD Foundation.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- */
- /*
- * An implementation of the H-TCP congestion control algorithm for FreeBSD,
- * based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and
- * Shorten. Originally released as part of the NewTCP research project at
- * Swinburne University of Technology's Centre for Advanced Internet
- * Architectures, Melbourne, Australia, which was made possible in part by a
- * grant from the Cisco University Research Program Fund at Community Foundation
- * Silicon Valley. More details are available at:
- * http://caia.swin.edu.au/urp/newtcp/
- */
- #include <sys/cdefs.h>
- __FBSDID("$FreeBSD$");
- #include <sys/param.h>
- #include <sys/kernel.h>
- #include <sys/limits.h>
- #include <sys/malloc.h>
- #include <sys/module.h>
- #include <sys/socket.h>
- #include <sys/socketvar.h>
- #include <sys/sysctl.h>
- #include <sys/systm.h>
- #include <net/vnet.h>
- #include <netinet/tcp.h>
- #include <netinet/tcp_seq.h>
- #include <netinet/tcp_timer.h>
- #include <netinet/tcp_var.h>
- #include <netinet/cc/cc.h>
- #include <netinet/cc/cc_module.h>
- /* Fixed point math shifts. */
- #define HTCP_SHIFT 8
- #define HTCP_ALPHA_INC_SHIFT 4
- #define HTCP_INIT_ALPHA 1
- #define HTCP_DELTA_L hz /* 1 sec in ticks. */
- #define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */
- #define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */
- #define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */
- #define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */
- /* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */
- #define HTCP_RTT_REF 100
- /* Don't trust SRTT until this many samples have been taken. */
- #define HTCP_MIN_RTT_SAMPLES 8
- /*
- * HTCP_CALC_ALPHA performs a fixed point math calculation to determine the
- * value of alpha, based on the function defined in the HTCP spec.
- *
- * i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2
- *
- * "diff" is passed in to the macro as "delta - delta_l" and is expected to be
- * in units of ticks.
- *
- * The joyousnous of fixed point maths means our function implementation looks a
- * little funky...
- *
- * In order to maintain some precision in the calculations, a fixed point shift
- * HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't
- * truncate the results too badly.
- *
- * The "16" value is the "1" term in the alpha function shifted up by
- * HTCP_ALPHA_INC_SHIFT
- *
- * The "160" value is the "10" multiplier in the alpha function multiplied by
- * 2^HTCP_ALPHA_INC_SHIFT
- *
- * Specifying these as constants reduces the computations required. After
- * up-shifting all the terms in the function and performing the required
- * calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to
- * ensure it is back in the correct range.
- *
- * The "hz" terms are required as kernels can be configured to run with
- * different tick timers, which we have to adjust for in the alpha calculation
- * (which originally was defined in terms of seconds).
- *
- * We also have to be careful to constrain the value of diff such that it won't
- * overflow whilst performing the calculation. The middle term i.e. (160 * diff)
- * / hz is the limiting factor in the calculation. We must constrain diff to be
- * less than the max size of an int divided by the constant 160 figure
- * i.e. diff < INT_MAX / 160
- *
- * NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the
- * constants used in this function!
- */
- #define HTCP_CALC_ALPHA(diff) \
- ((\
- (16) + \
- ((160 * (diff)) / hz) + \
- (((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \
- ) >> HTCP_ALPHA_INC_SHIFT)
- static void htcp_ack_received(struct cc_var *ccv, uint16_t type);
- static void htcp_cb_destroy(struct cc_var *ccv);
- static int htcp_cb_init(struct cc_var *ccv);
- static void htcp_cong_signal(struct cc_var *ccv, uint32_t type);
- static int htcp_mod_init(void);
- static void htcp_post_recovery(struct cc_var *ccv);
- static void htcp_recalc_alpha(struct cc_var *ccv);
- static void htcp_recalc_beta(struct cc_var *ccv);
- static void htcp_record_rtt(struct cc_var *ccv);
- static void htcp_ssthresh_update(struct cc_var *ccv);
- struct htcp {
- /* cwnd before entering cong recovery. */
- unsigned long prev_cwnd;
- /* cwnd additive increase parameter. */
- int alpha;
- /* cwnd multiplicative decrease parameter. */
- int beta;
- /* Largest rtt seen for the flow. */
- int maxrtt;
- /* Shortest rtt seen for the flow. */
- int minrtt;
- /* Time of last congestion event in ticks. */
- int t_last_cong;
- };
- static int htcp_rtt_ref;
- /*
- * The maximum number of ticks the value of diff can reach in
- * htcp_recalc_alpha() before alpha will stop increasing due to overflow.
- * See comment above HTCP_CALC_ALPHA for more info.
- */
- static int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10);
- /* Per-netstack vars. */
- VNET_DEFINE_STATIC(u_int, htcp_adaptive_backoff) = 0;
- VNET_DEFINE_STATIC(u_int, htcp_rtt_scaling) = 0;
- #define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff)
- #define V_htcp_rtt_scaling VNET(htcp_rtt_scaling)
- static MALLOC_DEFINE(M_HTCP, "htcp data",
- "Per connection data required for the HTCP congestion control algorithm");
- struct cc_algo htcp_cc_algo = {
- .name = "htcp",
- .ack_received = htcp_ack_received,
- .cb_destroy = htcp_cb_destroy,
- .cb_init = htcp_cb_init,
- .cong_signal = htcp_cong_signal,
- .mod_init = htcp_mod_init,
- .post_recovery = htcp_post_recovery,
- };
- static void
- htcp_ack_received(struct cc_var *ccv, uint16_t type)
- {
- struct htcp *htcp_data;
- htcp_data = ccv->cc_data;
- htcp_record_rtt(ccv);
- /*
- * Regular ACK and we're not in cong/fast recovery and we're cwnd
- * limited and we're either not doing ABC or are slow starting or are
- * doing ABC and we've sent a cwnd's worth of bytes.
- */
- if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
- (ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
- CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
- (V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
- htcp_recalc_beta(ccv);
- htcp_recalc_alpha(ccv);
- /*
- * Use the logic in NewReno ack_received() for slow start and
- * for the first HTCP_DELTA_L ticks after either the flow starts
- * or a congestion event (when alpha equals 1).
- */
- if (htcp_data->alpha == 1 ||
- CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh))
- newreno_cc_algo.ack_received(ccv, type);
- else {
- if (V_tcp_do_rfc3465) {
- /* Increment cwnd by alpha segments. */
- CCV(ccv, snd_cwnd) += htcp_data->alpha *
- CCV(ccv, t_maxseg);
- ccv->flags &= ~CCF_ABC_SENTAWND;
- } else
- /*
- * Increment cwnd by alpha/cwnd segments to
- * approximate an increase of alpha segments
- * per RTT.
- */
- CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
- HTCP_SHIFT) / (CCV(ccv, snd_cwnd) /
- CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg))
- >> HTCP_SHIFT;
- }
- }
- }
- static void
- htcp_cb_destroy(struct cc_var *ccv)
- {
- free(ccv->cc_data, M_HTCP);
- }
- static int
- htcp_cb_init(struct cc_var *ccv)
- {
- struct htcp *htcp_data;
- htcp_data = malloc(sizeof(struct htcp), M_HTCP, M_NOWAIT);
- if (htcp_data == NULL)
- return (ENOMEM);
- /* Init some key variables with sensible defaults. */
- htcp_data->alpha = HTCP_INIT_ALPHA;
- htcp_data->beta = HTCP_MINBETA;
- htcp_data->maxrtt = TCPTV_SRTTBASE;
- htcp_data->minrtt = TCPTV_SRTTBASE;
- htcp_data->prev_cwnd = 0;
- htcp_data->t_last_cong = ticks;
- ccv->cc_data = htcp_data;
- return (0);
- }
- /*
- * Perform any necessary tasks before we enter congestion recovery.
- */
- static void
- htcp_cong_signal(struct cc_var *ccv, uint32_t type)
- {
- struct htcp *htcp_data;
- u_int mss;
- htcp_data = ccv->cc_data;
- mss = tcp_maxseg(ccv->ccvc.tcp);
- switch (type) {
- case CC_NDUPACK:
- if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
- if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
- /*
- * Apply hysteresis to maxrtt to ensure
- * reductions in the RTT are reflected in our
- * measurements.
- */
- htcp_data->maxrtt = (htcp_data->minrtt +
- (htcp_data->maxrtt - htcp_data->minrtt) *
- 95) / 100;
- htcp_ssthresh_update(ccv);
- htcp_data->t_last_cong = ticks;
- htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
- }
- ENTER_RECOVERY(CCV(ccv, t_flags));
- }
- break;
- case CC_ECN:
- if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
- /*
- * Apply hysteresis to maxrtt to ensure reductions in
- * the RTT are reflected in our measurements.
- */
- htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt -
- htcp_data->minrtt) * 95) / 100;
- htcp_ssthresh_update(ccv);
- CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
- htcp_data->t_last_cong = ticks;
- htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
- ENTER_CONGRECOVERY(CCV(ccv, t_flags));
- }
- break;
- case CC_RTO:
- CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
- CCV(ccv, snd_cwnd)) / 2 / mss,
- 2) * mss;
- CCV(ccv, snd_cwnd) = mss;
- /*
- * Grab the current time and record it so we know when the
- * most recent congestion event was. Only record it when the
- * timeout has fired more than once, as there is a reasonable
- * chance the first one is a false alarm and may not indicate
- * congestion.
- */
- if (CCV(ccv, t_rxtshift) >= 2)
- htcp_data->t_last_cong = ticks;
- break;
- }
- }
- static int
- htcp_mod_init(void)
- {
- htcp_cc_algo.after_idle = newreno_cc_algo.after_idle;
- /*
- * HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in
- * units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units
- * as t_srtt.
- */
- htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000;
- return (0);
- }
- /*
- * Perform any necessary tasks before we exit congestion recovery.
- */
- static void
- htcp_post_recovery(struct cc_var *ccv)
- {
- int pipe;
- struct htcp *htcp_data;
- pipe = 0;
- htcp_data = ccv->cc_data;
- if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
- /*
- * If inflight data is less than ssthresh, set cwnd
- * conservatively to avoid a burst of data, as suggested in the
- * NewReno RFC. Otherwise, use the HTCP method.
- *
- * XXXLAS: Find a way to do this without needing curack
- */
- if (V_tcp_do_rfc6675_pipe)
- pipe = tcp_compute_pipe(ccv->ccvc.tcp);
- else
- pipe = CCV(ccv, snd_max) - ccv->curack;
- if (pipe < CCV(ccv, snd_ssthresh))
- /*
- * Ensure that cwnd down not collape to 1 MSS under
- * adverse conditions. Implements RFC6582
- */
- CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
- CCV(ccv, t_maxseg);
- else
- CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
- htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
- >> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
- }
- }
- static void
- htcp_recalc_alpha(struct cc_var *ccv)
- {
- struct htcp *htcp_data;
- int alpha, diff, now;
- htcp_data = ccv->cc_data;
- now = ticks;
- /*
- * If ticks has wrapped around (will happen approximately once every 49
- * days on a machine with the default kern.hz=1000) and a flow straddles
- * the wrap point, our alpha calcs will be completely wrong. We cut our
- * losses and restart alpha from scratch by setting t_last_cong = now -
- * HTCP_DELTA_L.
- *
- * This does not deflate our cwnd at all. It simply slows the rate cwnd
- * is growing by until alpha regains the value it held prior to taking
- * this drastic measure.
- */
- if (now < htcp_data->t_last_cong)
- htcp_data->t_last_cong = now - HTCP_DELTA_L;
- diff = now - htcp_data->t_last_cong - HTCP_DELTA_L;
- /* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */
- if (diff < htcp_max_diff) {
- /*
- * If it has been more than HTCP_DELTA_L ticks since congestion,
- * increase alpha according to the function defined in the spec.
- */
- if (diff > 0) {
- alpha = HTCP_CALC_ALPHA(diff);
- /*
- * Adaptive backoff fairness adjustment:
- * 2 * (1 - beta) * alpha_raw
- */
- if (V_htcp_adaptive_backoff)
- alpha = max(1, (2 * ((1 << HTCP_SHIFT) -
- htcp_data->beta) * alpha) >> HTCP_SHIFT);
- /*
- * RTT scaling: (RTT / RTT_ref) * alpha
- * alpha will be the raw value from HTCP_CALC_ALPHA() if
- * adaptive backoff is off, or the adjusted value if
- * adaptive backoff is on.
- */
- if (V_htcp_rtt_scaling)
- alpha = max(1, (min(max(HTCP_MINROWE,
- (CCV(ccv, t_srtt) << HTCP_SHIFT) /
- htcp_rtt_ref), HTCP_MAXROWE) * alpha)
- >> HTCP_SHIFT);
- } else
- alpha = 1;
- htcp_data->alpha = alpha;
- }
- }
- static void
- htcp_recalc_beta(struct cc_var *ccv)
- {
- struct htcp *htcp_data;
- htcp_data = ccv->cc_data;
- /*
- * TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so
- * we only calc beta if the connection's SRTT has been changed from its
- * initial value. beta is bounded to ensure it is always between
- * HTCP_MINBETA and HTCP_MAXBETA.
- */
- if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE &&
- htcp_data->maxrtt != TCPTV_SRTTBASE)
- htcp_data->beta = min(max(HTCP_MINBETA,
- (htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt),
- HTCP_MAXBETA);
- else
- htcp_data->beta = HTCP_MINBETA;
- }
- /*
- * Record the minimum and maximum RTT seen for the connection. These are used in
- * the calculation of beta if adaptive backoff is enabled.
- */
- static void
- htcp_record_rtt(struct cc_var *ccv)
- {
- struct htcp *htcp_data;
- htcp_data = ccv->cc_data;
- /* XXXLAS: Should there be some hysteresis for minrtt? */
- /*
- * Record the current SRTT as our minrtt if it's the smallest we've seen
- * or minrtt is currently equal to its initialised value. Ignore SRTT
- * until a min number of samples have been taken.
- */
- if ((CCV(ccv, t_srtt) < htcp_data->minrtt ||
- htcp_data->minrtt == TCPTV_SRTTBASE) &&
- (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES))
- htcp_data->minrtt = CCV(ccv, t_srtt);
- /*
- * Record the current SRTT as our maxrtt if it's the largest we've
- * seen. Ignore SRTT until a min number of samples have been taken.
- */
- if (CCV(ccv, t_srtt) > htcp_data->maxrtt
- && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)
- htcp_data->maxrtt = CCV(ccv, t_srtt);
- }
- /*
- * Update the ssthresh in the event of congestion.
- */
- static void
- htcp_ssthresh_update(struct cc_var *ccv)
- {
- struct htcp *htcp_data;
- htcp_data = ccv->cc_data;
- /*
- * On the first congestion event, set ssthresh to cwnd * 0.5, on
- * subsequent congestion events, set it to cwnd * beta.
- */
- if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT)
- CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
- HTCP_MINBETA) >> HTCP_SHIFT;
- else {
- htcp_recalc_beta(ccv);
- CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
- htcp_data->beta) >> HTCP_SHIFT;
- }
- }
- SYSCTL_DECL(_net_inet_tcp_cc_htcp);
- SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
- "H-TCP related settings");
- SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff,
- CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_adaptive_backoff), 0,
- "enable H-TCP adaptive backoff");
- SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling,
- CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_rtt_scaling), 0,
- "enable H-TCP RTT scaling");
- DECLARE_CC_MODULE(htcp, &htcp_cc_algo);
- MODULE_VERSION(htcp, 1);
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