Date: Sat, 28 May 2011 05:17:52 +0000 (UTC) From: Lawrence Stewart <lstewart@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org Subject: svn commit: r222403 - in stable/8/sys: modules/cc modules/cc/cc_cubic netinet/cc Message-ID: <201105280517.p4S5HqqF069320@svn.freebsd.org>
next in thread | raw e-mail | index | archive | help
Author: lstewart Date: Sat May 28 05:17:52 2011 New Revision: 222403 URL: http://svn.freebsd.org/changeset/base/222403 Log: MFC r216114,217683: Import a clean-room implementation of the experimental CUBIC congestion control algorithm based on the Internet-Draft "draft-rhee-tcpm-cubic-02.txt". It is implemented as a kernel module compatible with the recently committed modular congestion control framework. CUBIC was designed for provide increased throughput in fast and long-distance networks. It attempts to maintain fairness when competing with legacy NewReno TCP in lower speed scenarios where NewReno is able to operate adequately. The paper "CUBIC: A New TCP-Friendly High-Speed TCP Variant" provides additional detail. In collaboration with: David Hayes <dahayes at swin edu au> and Grenville Armitage <garmitage at swin edu au> Sponsored by: FreeBSD Foundation Reviewed by: rpaulo Added: stable/8/sys/modules/cc/cc_cubic/ - copied from r216114, head/sys/modules/cc/cc_cubic/ stable/8/sys/netinet/cc/cc_cubic.c - copied, changed from r216114, head/sys/netinet/cc/cc_cubic.c stable/8/sys/netinet/cc/cc_cubic.h - copied unchanged from r216114, head/sys/netinet/cc/cc_cubic.h Modified: stable/8/sys/modules/cc/Makefile Directory Properties: stable/8/sys/ (props changed) stable/8/sys/amd64/include/xen/ (props changed) stable/8/sys/cddl/contrib/opensolaris/ (props changed) stable/8/sys/contrib/dev/acpica/ (props changed) stable/8/sys/contrib/pf/ (props changed) Modified: stable/8/sys/modules/cc/Makefile ============================================================================== --- stable/8/sys/modules/cc/Makefile Sat May 28 05:04:53 2011 (r222402) +++ stable/8/sys/modules/cc/Makefile Sat May 28 05:17:52 2011 (r222403) @@ -1,5 +1,5 @@ # $FreeBSD$ -SUBDIR= +SUBDIR= cc_cubic .include <bsd.subdir.mk> Copied and modified: stable/8/sys/netinet/cc/cc_cubic.c (from r216114, head/sys/netinet/cc/cc_cubic.c) ============================================================================== --- head/sys/netinet/cc/cc_cubic.c Thu Dec 2 06:05:44 2010 (r216114, copy source) +++ stable/8/sys/netinet/cc/cc_cubic.c Sat May 28 05:17:52 2011 (r222403) @@ -212,7 +212,7 @@ cubic_cb_init(struct cc_var *ccv) /* 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 = TCPTV_SRTTBASE; + cubic_data->mean_rtt_ticks = 1; ccv->cc_data = cubic_data; @@ -328,12 +328,11 @@ cubic_post_recovery(struct cc_var *ccv) cubic_data->t_last_cong = ticks; /* Calculate the average RTT between congestion epochs. */ - if (cubic_data->epoch_ack_count > 0 && cubic_data->sum_rtt_ticks > 0) + 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); - else - /* For safety. */ - cubic_data->mean_rtt_ticks = cubic_data->min_rtt_ticks; + } cubic_data->epoch_ack_count = 0; cubic_data->sum_rtt_ticks = 0; @@ -362,9 +361,21 @@ cubic_record_rtt(struct cc_var *ccv) * 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 == 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++; Copied: stable/8/sys/netinet/cc/cc_cubic.h (from r216114, head/sys/netinet/cc/cc_cubic.h) ============================================================================== --- /dev/null 00:00:00 1970 (empty, because file is newly added) +++ stable/8/sys/netinet/cc/cc_cubic.h Sat May 28 05:17:52 2011 (r222403, copy of r216114, head/sys/netinet/cc/cc_cubic.h) @@ -0,0 +1,229 @@ +/*- + * Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org> + * 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, 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. + * + * $FreeBSD$ + */ + +#ifndef _NETINET_CC_CUBIC_H_ +#define _NETINET_CC_CUBIC_H_ + +/* Number of bits of precision for fixed point math calcs. */ +#define CUBIC_SHIFT 8 + +#define CUBIC_SHIFT_4 32 + +/* 0.5 << CUBIC_SHIFT. */ +#define RENO_BETA 128 + +/* ~0.8 << CUBIC_SHIFT. */ +#define CUBIC_BETA 204 + +/* ~0.2 << CUBIC_SHIFT. */ +#define ONE_SUB_CUBIC_BETA 51 + +/* 3 * ONE_SUB_CUBIC_BETA. */ +#define THREE_X_PT2 153 + +/* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */ +#define TWO_SUB_PT2 461 + +/* ~0.4 << CUBIC_SHIFT. */ +#define CUBIC_C_FACTOR 102 + +/* CUBIC fast convergence factor: ~0.9 << CUBIC_SHIFT. */ +#define CUBIC_FC_FACTOR 230 + +/* Don't trust s_rtt until this many rtt samples have been taken. */ +#define CUBIC_MIN_RTT_SAMPLES 8 + +/* Userland only bits. */ +#ifndef _KERNEL + +extern int hz; + +/* + * Implementation based on the formulae found in the CUBIC Internet Draft + * "draft-rhee-tcpm-cubic-02". + * + * Note BETA used in cc_cubic is equal to (1-beta) in the I-D + */ + +static __inline float +theoretical_cubic_k(double wmax_pkts) +{ + double C; + + C = 0.4; + + return (pow((wmax_pkts * 0.2) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT)); +} + +static __inline unsigned long +theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss) +{ + double C, wmax_pkts; + + C = 0.4; + wmax_pkts = wmax / (double)smss; + + return (smss * (wmax_pkts + + (C * pow(ticks_since_cong / (double)hz - + theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0)))); +} + +static __inline unsigned long +theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, + uint32_t smss) +{ + + return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss)); +} + +static __inline unsigned long +theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, + uint32_t smss) +{ + + return ((wmax * 0.8) + ((3 * 0.2) / (2 - 0.2) * + (ticks_since_cong / (float)rtt_ticks) * smss)); +} + +#endif /* !_KERNEL */ + +/* + * Compute the CUBIC K value used in the cwnd calculation, using an + * implementation of eqn 2 in the I-D. The method used + * here is adapted from Apple Computer Technical Report #KT-32. + */ +static __inline int64_t +cubic_k(unsigned long wmax_pkts) +{ + int64_t s, K; + uint16_t p; + + K = s = 0; + p = 0; + + /* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */ + s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR; + + /* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */ + while (s >= 256) { + s >>= 3; + p++; + } + + /* + * Some magic constants taken from the Apple TR with appropriate + * shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 << + * CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT. + */ + K = (((s * 275) >> CUBIC_SHIFT) + 98) - + (((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT); + + /* Multiply by 2^p to undo the rebasing of s from above. */ + return (K <<= p); +} + +/* + * Compute the new cwnd value using an implementation of eqn 1 from the I-D. + * Thanks to Kip Macy for help debugging this function. + * + * XXXLAS: Characterise bounds for overflow. + */ +static __inline unsigned long +cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K) +{ + int64_t cwnd; + + /* K is in fixed point form with CUBIC_SHIFT worth of precision. */ + + /* t - K, with CUBIC_SHIFT worth of precision. */ + cwnd = ((int64_t)(ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz; + + /* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */ + cwnd *= (cwnd * cwnd); + + /* + * C(t - K)^3 + wmax + * The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of + * CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above, + * and an extra from multiplying through by CUBIC_C_FACTOR. + */ + cwnd = ((cwnd * CUBIC_C_FACTOR * smss) >> CUBIC_SHIFT_4) + wmax; + + return ((unsigned long)cwnd); +} + +/* + * Compute an approximation of the NewReno cwnd some number of ticks after a + * congestion event. RTT should be the average RTT estimate for the path + * measured over the previous congestion epoch and wmax is the value of cwnd at + * the last congestion event. The "TCP friendly" concept in the CUBIC I-D is + * rather tricky to understand and it turns out this function is not required. + * It is left here for reference. + */ +static __inline unsigned long +reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, + uint32_t smss) +{ + + /* + * For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT + * W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in + * bytes, we have to multiply by smss. + */ + return (((wmax * RENO_BETA) + (((ticks_since_cong * smss) + << CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT); +} + +/* + * Compute an approximation of the "TCP friendly" cwnd some number of ticks + * after a congestion event that is designed to yield the same average cwnd as + * NewReno while using CUBIC's beta of 0.8. RTT should be the average RTT + * estimate for the path measured over the previous congestion epoch and wmax is + * the value of cwnd at the last congestion event. + */ +static __inline unsigned long +tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax, + uint32_t smss) +{ + + /* Equation 4 of I-D. */ + return (((wmax * CUBIC_BETA) + (((THREE_X_PT2 * ticks_since_cong * + smss) << CUBIC_SHIFT) / TWO_SUB_PT2 / rtt_ticks)) >> CUBIC_SHIFT); +} + +#endif /* _NETINET_CC_CUBIC_H_ */
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201105280517.p4S5HqqF069320>