/*- * SPDX-License-Identifier: BSD-2-Clause * * Copyright (c) 2008-2010 Lawrence Stewart * Copyright (c) 2010 The FreeBSD Foundation * All rights reserved. * * This software was developed by Lawrence Stewart while studying at the Centre * for Advanced Internet Architectures, Swinburne University of Technology, 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 CUBIC congestion control algorithm for FreeBSD, * based on the Internet Draft "draft-rhee-tcpm-cubic-02" by Rhee, Xu and Ha. * 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 #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include static void cubic_ack_received(struct cc_var *ccv, uint16_t type); static void cubic_cb_destroy(struct cc_var *ccv); static int cubic_cb_init(struct cc_var *ccv); static void cubic_cong_signal(struct cc_var *ccv, uint32_t type); static void cubic_conn_init(struct cc_var *ccv); static int cubic_mod_init(void); static void cubic_post_recovery(struct cc_var *ccv); static void cubic_record_rtt(struct cc_var *ccv); static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg); static void cubic_after_idle(struct cc_var *ccv); struct cubic { /* Cubic K in fixed point form with CUBIC_SHIFT worth of precision. */ int64_t K; /* Sum of RTT samples across an epoch in ticks. */ int64_t sum_rtt_ticks; /* cwnd at the most recent congestion event. */ unsigned long max_cwnd; /* cwnd at the previous congestion event. */ unsigned long prev_max_cwnd; /* A copy of prev_max_cwnd. Used for CC_RTO_ERR */ unsigned long prev_max_cwnd_cp; /* various flags */ uint32_t flags; #define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */ #define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */ #define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */ #define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */ /* Minimum observed rtt in ticks. */ int min_rtt_ticks; /* Mean observed rtt between congestion epochs. */ int mean_rtt_ticks; /* ACKs since last congestion event. */ int epoch_ack_count; /* Timestamp (in ticks) of arriving in congestion avoidance from last * congestion event. */ int t_last_cong; /* Timestamp (in ticks) of a previous congestion event. Used for * CC_RTO_ERR. */ int t_last_cong_prev; }; static MALLOC_DEFINE(M_CUBIC, "cubic data", "Per connection data required for the CUBIC congestion control algorithm"); struct cc_algo cubic_cc_algo = { .name = "cubic", .ack_received = cubic_ack_received, .cb_destroy = cubic_cb_destroy, .cb_init = cubic_cb_init, .cong_signal = cubic_cong_signal, .conn_init = cubic_conn_init, .mod_init = cubic_mod_init, .post_recovery = cubic_post_recovery, .after_idle = cubic_after_idle, }; static void cubic_ack_received(struct cc_var *ccv, uint16_t type) { struct cubic *cubic_data; unsigned long w_tf, w_cubic_next; int ticks_since_cong; cubic_data = ccv->cc_data; cubic_record_rtt(ccv); /* * For a regular ACK and we're not in cong/fast recovery and * we're cwnd limited, always recalculate cwnd. */ if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && (ccv->flags & CCF_CWND_LIMITED)) { /* Use the logic in NewReno ack_received() for slow start. */ if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) || cubic_data->min_rtt_ticks == TCPTV_SRTTBASE) { cubic_data->flags |= CUBICFLAG_IN_SLOWSTART; newreno_cc_algo.ack_received(ccv, type); } else { if ((cubic_data->flags & CUBICFLAG_RTO_EVENT) && (cubic_data->flags & CUBICFLAG_IN_SLOWSTART)) { /* RFC8312 Section 4.7 */ cubic_data->flags &= ~(CUBICFLAG_RTO_EVENT | CUBICFLAG_IN_SLOWSTART); cubic_data->max_cwnd = CCV(ccv, snd_cwnd); cubic_data->t_last_cong = ticks; cubic_data->K = 0; } else if (cubic_data->flags & (CUBICFLAG_IN_SLOWSTART | CUBICFLAG_IN_APPLIMIT)) { cubic_data->flags &= ~(CUBICFLAG_IN_SLOWSTART | CUBICFLAG_IN_APPLIMIT); cubic_data->t_last_cong = ticks; cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); } if ((ticks_since_cong = ticks - cubic_data->t_last_cong) < 0) { /* * dragging t_last_cong along */ ticks_since_cong = INT_MAX; cubic_data->t_last_cong = ticks - INT_MAX; } /* * The mean RTT is used to best reflect the equations in * the I-D. Using min_rtt in the tf_cwnd calculation * causes w_tf to grow much faster than it should if the * RTT is dominated by network buffering rather than * propagation delay. */ w_tf = tf_cwnd(ticks_since_cong, cubic_data->mean_rtt_ticks, cubic_data->max_cwnd, CCV(ccv, t_maxseg)); w_cubic_next = cubic_cwnd(ticks_since_cong + cubic_data->mean_rtt_ticks, cubic_data->max_cwnd, CCV(ccv, t_maxseg), cubic_data->K); ccv->flags &= ~CCF_ABC_SENTAWND; if (w_cubic_next < w_tf) { /* * TCP-friendly region, follow tf * cwnd growth. */ if (CCV(ccv, snd_cwnd) < w_tf) CCV(ccv, snd_cwnd) = ulmin(w_tf, INT_MAX); } else if (CCV(ccv, snd_cwnd) < w_cubic_next) { /* * Concave or convex region, follow CUBIC * cwnd growth. * Only update snd_cwnd, if it doesn't shrink. */ CCV(ccv, snd_cwnd) = ulmin(w_cubic_next, INT_MAX); } /* * If we're not in slow start and we're probing for a * new cwnd limit at the start of a connection * (happens when hostcache has a relevant entry), * keep updating our current estimate of the * max_cwnd. */ if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) && cubic_data->max_cwnd < CCV(ccv, snd_cwnd)) { cubic_data->max_cwnd = CCV(ccv, snd_cwnd); cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); } } } else if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) && !(ccv->flags & CCF_CWND_LIMITED)) { cubic_data->flags |= CUBICFLAG_IN_APPLIMIT; } } /* * This is a Cubic specific implementation of after_idle. * - Reset cwnd by calling New Reno implementation of after_idle. * - Reset t_last_cong. */ static void cubic_after_idle(struct cc_var *ccv) { struct cubic *cubic_data; cubic_data = ccv->cc_data; cubic_data->max_cwnd = ulmax(cubic_data->max_cwnd, CCV(ccv, snd_cwnd)); cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg)); newreno_cc_algo.after_idle(ccv); cubic_data->t_last_cong = ticks; } static void cubic_cb_destroy(struct cc_var *ccv) { free(ccv->cc_data, M_CUBIC); } static int cubic_cb_init(struct cc_var *ccv) { struct cubic *cubic_data; cubic_data = malloc(sizeof(struct cubic), M_CUBIC, M_NOWAIT|M_ZERO); if (cubic_data == NULL) return (ENOMEM); /* Init some key variables with sensible defaults. */ cubic_data->t_last_cong = ticks; cubic_data->min_rtt_ticks = TCPTV_SRTTBASE; cubic_data->mean_rtt_ticks = 1; ccv->cc_data = cubic_data; return (0); } /* * Perform any necessary tasks before we enter congestion recovery. */ static void cubic_cong_signal(struct cc_var *ccv, uint32_t type) { struct cubic *cubic_data; u_int mss; cubic_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))) { cubic_ssthresh_update(ccv, mss); cubic_data->flags |= CUBICFLAG_CONG_EVENT; cubic_data->t_last_cong = ticks; cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); } ENTER_RECOVERY(CCV(ccv, t_flags)); } break; case CC_ECN: if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) { cubic_ssthresh_update(ccv, mss); cubic_data->flags |= CUBICFLAG_CONG_EVENT; cubic_data->t_last_cong = ticks; cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh); ENTER_CONGRECOVERY(CCV(ccv, t_flags)); } break; case CC_RTO: /* RFC8312 Section 4.7 */ if (CCV(ccv, t_rxtshift) == 1) { cubic_data->t_last_cong_prev = cubic_data->t_last_cong; cubic_data->prev_max_cwnd_cp = cubic_data->prev_max_cwnd; } cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT; cubic_data->prev_max_cwnd = cubic_data->max_cwnd; CCV(ccv, snd_ssthresh) = ((uint64_t)CCV(ccv, snd_cwnd) * CUBIC_BETA) >> CUBIC_SHIFT; CCV(ccv, snd_cwnd) = mss; break; case CC_RTO_ERR: cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT); cubic_data->max_cwnd = cubic_data->prev_max_cwnd; cubic_data->prev_max_cwnd = cubic_data->prev_max_cwnd_cp; cubic_data->t_last_cong = cubic_data->t_last_cong_prev; cubic_data->K = cubic_k(cubic_data->max_cwnd / mss); break; } } static void cubic_conn_init(struct cc_var *ccv) { struct cubic *cubic_data; cubic_data = ccv->cc_data; /* * Ensure we have a sane initial value for max_cwnd recorded. Without * this here bad things happen when entries from the TCP hostcache * get used. */ cubic_data->max_cwnd = CCV(ccv, snd_cwnd); } static int cubic_mod_init(void) { return (0); } /* * Perform any necessary tasks before we exit congestion recovery. */ static void cubic_post_recovery(struct cc_var *ccv) { struct cubic *cubic_data; int pipe; cubic_data = ccv->cc_data; pipe = 0; 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 CUBIC 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 does not collapse to 1 MSS under * adverse conditions. Implements RFC6582 */ CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) + CCV(ccv, t_maxseg); else /* Update cwnd based on beta and adjusted max_cwnd. */ CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->max_cwnd * CUBIC_BETA) >> CUBIC_SHIFT, 2 * CCV(ccv, t_maxseg)); } /* Calculate the average RTT between congestion epochs. */ if (cubic_data->epoch_ack_count > 0 && cubic_data->sum_rtt_ticks >= cubic_data->epoch_ack_count) { cubic_data->mean_rtt_ticks = (int)(cubic_data->sum_rtt_ticks / cubic_data->epoch_ack_count); } cubic_data->epoch_ack_count = 0; cubic_data->sum_rtt_ticks = 0; } /* * Record the min RTT and sum samples for the epoch average RTT calculation. */ static void cubic_record_rtt(struct cc_var *ccv) { struct cubic *cubic_data; int t_srtt_ticks; /* Ignore srtt until a min number of samples have been taken. */ if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) { cubic_data = ccv->cc_data; t_srtt_ticks = CCV(ccv, t_srtt) / TCP_RTT_SCALE; /* * Record the current SRTT as our minrtt if it's the smallest * we've seen or minrtt is currently equal to its initialised * value. * * XXXLAS: Should there be some hysteresis for minrtt? */ if ((t_srtt_ticks < cubic_data->min_rtt_ticks || cubic_data->min_rtt_ticks == TCPTV_SRTTBASE)) { cubic_data->min_rtt_ticks = max(1, t_srtt_ticks); /* * If the connection is within its first congestion * epoch, ensure we prime mean_rtt_ticks with a * reasonable value until the epoch average RTT is * calculated in cubic_post_recovery(). */ if (cubic_data->min_rtt_ticks > cubic_data->mean_rtt_ticks) cubic_data->mean_rtt_ticks = cubic_data->min_rtt_ticks; } /* Sum samples for epoch average RTT calculation. */ cubic_data->sum_rtt_ticks += t_srtt_ticks; cubic_data->epoch_ack_count++; } } /* * Update the ssthresh in the event of congestion. */ static void cubic_ssthresh_update(struct cc_var *ccv, uint32_t maxseg) { struct cubic *cubic_data; uint32_t ssthresh; uint32_t cwnd; cubic_data = ccv->cc_data; cwnd = CCV(ccv, snd_cwnd); /* Fast convergence heuristic. */ if (cwnd < cubic_data->max_cwnd) { cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT; } cubic_data->prev_max_cwnd = cubic_data->max_cwnd; cubic_data->max_cwnd = cwnd; /* * On the first congestion event, set ssthresh to cwnd * 0.5 * and reduce max_cwnd to cwnd * beta. This aligns the cubic concave * region appropriately. On subsequent congestion events, set * ssthresh to cwnd * beta. */ if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) { ssthresh = cwnd >> 1; cubic_data->max_cwnd = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; } else { ssthresh = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT; } CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg); } DECLARE_CC_MODULE(cubic, &cubic_cc_algo); MODULE_VERSION(cubic, 1);