ea6d0de299
Consistently refer to the CUBIC congestion control mechanism in uppercase throughout all comments. No functional change. Reviewed By: #transport, tuexen, mav, guest-ccui, emaste Sponsored by: NetApp, Inc. Differential Revision: https://reviews.freebsd.org/D36547
299 lines
9.0 KiB
C
299 lines
9.0 KiB
C
/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright (c) 2008-2010 Lawrence Stewart <lstewart@freebsd.org>
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* Copyright (c) 2010 The FreeBSD Foundation
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* All rights reserved.
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*
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* This software was developed by Lawrence Stewart while studying at the Centre
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* for Advanced Internet Architectures, Swinburne University of Technology, made
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* possible in part by a grant from the Cisco University Research Program Fund
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* at Community Foundation Silicon Valley.
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*
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* Portions of this software were developed at the Centre for Advanced
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* Internet Architectures, Swinburne University of Technology, Melbourne,
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* Australia by David Hayes under sponsorship from the FreeBSD Foundation.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef _NETINET_CC_CUBIC_H_
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#define _NETINET_CC_CUBIC_H_
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#include <sys/limits.h>
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/* Number of bits of precision for fixed point math calcs. */
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#define CUBIC_SHIFT 8
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#define CUBIC_SHIFT_4 32
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/* 0.5 << CUBIC_SHIFT. */
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#define RENO_BETA 128
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/* ~0.7 << CUBIC_SHIFT. */
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#define CUBIC_BETA 179
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/* ~0.3 << CUBIC_SHIFT. */
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#define ONE_SUB_CUBIC_BETA 77
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/* 3 * ONE_SUB_CUBIC_BETA. */
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#define THREE_X_PT3 231
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/* (2 << CUBIC_SHIFT) - ONE_SUB_CUBIC_BETA. */
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#define TWO_SUB_PT3 435
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/* ~0.4 << CUBIC_SHIFT. */
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#define CUBIC_C_FACTOR 102
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/* CUBIC fast convergence factor: (1+beta_cubic)/2. */
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#define CUBIC_FC_FACTOR 217
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/* Don't trust s_rtt until this many rtt samples have been taken. */
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#define CUBIC_MIN_RTT_SAMPLES 8
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/*
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* (2^21)^3 is long max. Dividing (2^63) by Cubic_C_factor
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* and taking cube-root yields 448845 as the effective useful limit
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*/
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#define CUBED_ROOT_MAX_ULONG 448845
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/* Flags used in the cubic structure */
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#define CUBICFLAG_CONG_EVENT 0x00000001 /* congestion experienced */
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#define CUBICFLAG_IN_SLOWSTART 0x00000002 /* in slow start */
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#define CUBICFLAG_IN_APPLIMIT 0x00000004 /* application limited */
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#define CUBICFLAG_RTO_EVENT 0x00000008 /* RTO experienced */
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#define CUBICFLAG_HYSTART_ENABLED 0x00000010 /* Hystart++ is enabled */
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#define CUBICFLAG_HYSTART_IN_CSS 0x00000020 /* We are in Hystart++ CSS */
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/* Kernel only bits */
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#ifdef _KERNEL
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struct cubic {
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/* CUBIC K in fixed point form with CUBIC_SHIFT worth of precision. */
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int64_t K;
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/* Sum of RTT samples across an epoch in ticks. */
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int64_t sum_rtt_ticks;
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/* cwnd at the most recent congestion event. */
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unsigned long max_cwnd;
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/* cwnd at the previous congestion event. */
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unsigned long prev_max_cwnd;
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/* A copy of prev_max_cwnd. Used for CC_RTO_ERR */
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unsigned long prev_max_cwnd_cp;
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/* various flags */
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uint32_t flags;
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/* Minimum observed rtt in ticks. */
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int min_rtt_ticks;
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/* Mean observed rtt between congestion epochs. */
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int mean_rtt_ticks;
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/* ACKs since last congestion event. */
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int epoch_ack_count;
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/* Timestamp (in ticks) of arriving in congestion avoidance from last
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* congestion event.
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*/
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int t_last_cong;
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/* Timestamp (in ticks) of a previous congestion event. Used for
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* CC_RTO_ERR.
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*/
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int t_last_cong_prev;
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uint32_t css_baseline_minrtt;
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uint32_t css_current_round_minrtt;
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uint32_t css_lastround_minrtt;
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uint32_t css_rttsample_count;
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uint32_t css_entered_at_round;
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uint32_t css_current_round;
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uint32_t css_fas_at_css_entry;
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uint32_t css_lowrtt_fas;
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uint32_t css_last_fas;
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};
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#endif
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/* Userland only bits. */
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#ifndef _KERNEL
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extern int hz;
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/*
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* Implementation based on the formulae found in the CUBIC Internet Draft
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* "draft-ietf-tcpm-cubic-04".
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*
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*/
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static __inline float
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theoretical_cubic_k(double wmax_pkts)
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{
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double C;
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C = 0.4;
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return (pow((wmax_pkts * 0.3) / C, (1.0 / 3.0)) * pow(2, CUBIC_SHIFT));
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}
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static __inline unsigned long
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theoretical_cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss)
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{
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double C, wmax_pkts;
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C = 0.4;
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wmax_pkts = wmax / (double)smss;
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return (smss * (wmax_pkts +
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(C * pow(ticks_since_cong / (double)hz -
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theoretical_cubic_k(wmax_pkts) / pow(2, CUBIC_SHIFT), 3.0))));
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}
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static __inline unsigned long
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theoretical_reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
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uint32_t smss)
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{
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return ((wmax * 0.5) + ((ticks_since_cong / (float)rtt_ticks) * smss));
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}
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static __inline unsigned long
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theoretical_tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
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uint32_t smss)
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{
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return ((wmax * 0.7) + ((3 * 0.3) / (2 - 0.3) *
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(ticks_since_cong / (float)rtt_ticks) * smss));
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}
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#endif /* !_KERNEL */
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/*
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* Compute the CUBIC K value used in the cwnd calculation, using an
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* implementation of eqn 2 in the I-D. The method used
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* here is adapted from Apple Computer Technical Report #KT-32.
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*/
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static __inline int64_t
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cubic_k(unsigned long wmax_pkts)
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{
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int64_t s, K;
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uint16_t p;
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K = s = 0;
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p = 0;
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/* (wmax * beta)/C with CUBIC_SHIFT worth of precision. */
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s = ((wmax_pkts * ONE_SUB_CUBIC_BETA) << CUBIC_SHIFT) / CUBIC_C_FACTOR;
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/* Rebase s to be between 1 and 1/8 with a shift of CUBIC_SHIFT. */
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while (s >= 256) {
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s >>= 3;
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p++;
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}
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/*
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* Some magic constants taken from the Apple TR with appropriate
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* shifts: 275 == 1.072302 << CUBIC_SHIFT, 98 == 0.3812513 <<
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* CUBIC_SHIFT, 120 == 0.46946116 << CUBIC_SHIFT.
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*/
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K = (((s * 275) >> CUBIC_SHIFT) + 98) -
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(((s * s * 120) >> CUBIC_SHIFT) >> CUBIC_SHIFT);
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/* Multiply by 2^p to undo the rebasing of s from above. */
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return (K <<= p);
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}
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/*
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* Compute the new cwnd value using an implementation of eqn 1 from the I-D.
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* Thanks to Kip Macy for help debugging this function.
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*
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* XXXLAS: Characterise bounds for overflow.
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*/
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static __inline unsigned long
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cubic_cwnd(int ticks_since_cong, unsigned long wmax, uint32_t smss, int64_t K)
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{
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int64_t cwnd;
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/* K is in fixed point form with CUBIC_SHIFT worth of precision. */
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/* t - K, with CUBIC_SHIFT worth of precision. */
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cwnd = (((int64_t)ticks_since_cong << CUBIC_SHIFT) - (K * hz)) / hz;
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if (cwnd > CUBED_ROOT_MAX_ULONG)
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return INT_MAX;
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if (cwnd < -CUBED_ROOT_MAX_ULONG)
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return 0;
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/* (t - K)^3, with CUBIC_SHIFT^3 worth of precision. */
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cwnd *= (cwnd * cwnd);
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/*
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* C(t - K)^3 + wmax
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* The down shift by CUBIC_SHIFT_4 is because cwnd has 4 lots of
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* CUBIC_SHIFT included in the value. 3 from the cubing of cwnd above,
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* and an extra from multiplying through by CUBIC_C_FACTOR.
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*/
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cwnd = ((cwnd * CUBIC_C_FACTOR) >> CUBIC_SHIFT_4) * smss + wmax;
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/*
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* for negative cwnd, limiting to zero as lower bound
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*/
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return (lmax(0,cwnd));
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}
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/*
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* Compute an approximation of the NewReno cwnd some number of ticks after a
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* congestion event. RTT should be the average RTT estimate for the path
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* measured over the previous congestion epoch and wmax is the value of cwnd at
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* the last congestion event. The "TCP friendly" concept in the CUBIC I-D is
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* rather tricky to understand and it turns out this function is not required.
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* It is left here for reference.
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*/
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static __inline unsigned long
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reno_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
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uint32_t smss)
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{
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/*
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* For NewReno, beta = 0.5, therefore: W_tcp(t) = wmax*0.5 + t/RTT
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* W_tcp(t) deals with cwnd/wmax in pkts, so because our cwnd is in
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* bytes, we have to multiply by smss.
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*/
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return (((wmax * RENO_BETA) + (((ticks_since_cong * smss)
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<< CUBIC_SHIFT) / rtt_ticks)) >> CUBIC_SHIFT);
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}
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/*
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* Compute an approximation of the "TCP friendly" cwnd some number of ticks
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* after a congestion event that is designed to yield the same average cwnd as
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* NewReno while using CUBIC's beta of 0.7. RTT should be the average RTT
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* estimate for the path measured over the previous congestion epoch and wmax is
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* the value of cwnd at the last congestion event.
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*/
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static __inline unsigned long
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tf_cwnd(int ticks_since_cong, int rtt_ticks, unsigned long wmax,
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uint32_t smss)
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{
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/* Equation 4 of I-D. */
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return (((wmax * CUBIC_BETA) +
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(((THREE_X_PT3 * (unsigned long)ticks_since_cong *
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(unsigned long)smss) << CUBIC_SHIFT) / (TWO_SUB_PT3 * rtt_ticks)))
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>> CUBIC_SHIFT);
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}
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#endif /* _NETINET_CC_CUBIC_H_ */
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