/*- * SPDX-License-Identifier: BSD-2-Clause * * 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/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 <net/route.h> #include <net/route/nhop.h> #include <netinet/in_pcb.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, ccsignal_t type); static void htcp_cb_destroy(struct cc_var *ccv); static int htcp_cb_init(struct cc_var *ccv, void *ptr); static void htcp_cong_signal(struct cc_var *ccv, ccsignal_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); static size_t htcp_data_sz(void); 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) 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, .cc_data_sz = htcp_data_sz, .after_idle = newreno_cc_after_idle, }; static void htcp_ack_received(struct cc_var *ccv, ccsignal_t type) { struct htcp *htcp_data; uint32_t mss = tcp_fixed_maxseg(ccv->tp); 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_ack_received(ccv, type); else { if (V_tcp_do_rfc3465) { /* Increment cwnd by alpha segments. */ CCV(ccv, snd_cwnd) += htcp_data->alpha * mss; 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) / (max(1, CCV(ccv, snd_cwnd) / mss))) * mss) >> HTCP_SHIFT; } } } static void htcp_cb_destroy(struct cc_var *ccv) { free(ccv->cc_data, M_CC_MEM); } static size_t htcp_data_sz(void) { return(sizeof(struct htcp)); } static int htcp_cb_init(struct cc_var *ccv, void *ptr) { struct htcp *htcp_data; INP_WLOCK_ASSERT(tptoinpcb(ccv->tp)); if (ptr == NULL) { htcp_data = malloc(sizeof(struct htcp), M_CC_MEM, M_NOWAIT); if (htcp_data == NULL) return (ENOMEM); } else htcp_data = ptr; /* 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, ccsignal_t type) { struct htcp *htcp_data; uint32_t mss, pipe; htcp_data = ccv->cc_data; mss = tcp_fixed_maxseg(ccv->tp); 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: if (CCV(ccv, t_rxtshift) == 1) { pipe = tcp_compute_pipe(ccv->tp); CCV(ccv, snd_ssthresh) = max(2, min(CCV(ccv, snd_wnd), pipe) / 2 / mss) * 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; default: break; } } static int htcp_mod_init(void) { /* * 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; uint32_t mss = tcp_fixed_maxseg(ccv->tp); 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. */ pipe = tcp_compute_pipe(ccv->tp); 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, mss) + mss; else CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta * htcp_data->prev_cwnd / mss) >> HTCP_SHIFT)) * mss; } } 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, (tcp_get_srtt(ccv->tp, TCP_TMR_GRANULARITY_TICKS) << 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 ((tcp_get_srtt(ccv->tp, TCP_TMR_GRANULARITY_TICKS) < htcp_data->minrtt || htcp_data->minrtt == TCPTV_SRTTBASE) && (CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)) htcp_data->minrtt = tcp_get_srtt(ccv->tp, TCP_TMR_GRANULARITY_TICKS); /* * 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 (tcp_get_srtt(ccv->tp, TCP_TMR_GRANULARITY_TICKS) > htcp_data->maxrtt && CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES) htcp_data->maxrtt = tcp_get_srtt(ccv->tp, TCP_TMR_GRANULARITY_TICKS); } /* * 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, 2);
