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https://github.com/freebsd/freebsd-src
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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 (older patch from a few weeks ago) MFC after: 3 months
This commit is contained in:
Lawrence Stewart
parent
5a7bfc90a9
commit
67fef78ba4
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=216114
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@ -1,5 +1,5 @@
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# $FreeBSD$
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SUBDIR=
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SUBDIR= cc_cubic
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.include <bsd.subdir.mk>
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9
sys/modules/cc/cc_cubic/Makefile
Normal file
9
sys/modules/cc/cc_cubic/Makefile
Normal file
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@ -0,0 +1,9 @@
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# $FreeBSD$
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.include <bsd.own.mk>
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.PATH: ${.CURDIR}/../../../netinet/cc
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KMOD= cc_cubic
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SRCS= cc_cubic.c
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.include <bsd.kmod.mk>
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396
sys/netinet/cc/cc_cubic.c
Normal file
396
sys/netinet/cc/cc_cubic.c
Normal file
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@ -0,0 +1,396 @@
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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, made possible in
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* part by a grant from the Cisco University Research Program Fund at Community
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* 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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/*
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* An implementation of the CUBIC congestion control algorithm for FreeBSD,
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* based on the Internet Draft "draft-rhee-tcpm-cubic-02" by Rhee, Xu and Ha.
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* Originally released as part of the NewTCP research project at Swinburne
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* University's Centre for Advanced Internet Architectures, Melbourne,
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* Australia, which was made possible in part by a grant from the Cisco
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* University Research Program Fund at Community Foundation Silicon Valley. More
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* details are available at:
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* http://caia.swin.edu.au/urp/newtcp/
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/malloc.h>
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#include <sys/module.h>
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#include <sys/socket.h>
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#include <sys/socketvar.h>
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#include <sys/sysctl.h>
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#include <sys/systm.h>
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#include <net/vnet.h>
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#include <netinet/cc.h>
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#include <netinet/tcp_seq.h>
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#include <netinet/tcp_timer.h>
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#include <netinet/tcp_var.h>
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#include <netinet/cc/cc_cubic.h>
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#include <netinet/cc/cc_module.h>
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static void cubic_ack_received(struct cc_var *ccv, uint16_t type);
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static void cubic_cb_destroy(struct cc_var *ccv);
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static int cubic_cb_init(struct cc_var *ccv);
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static void cubic_cong_signal(struct cc_var *ccv, uint32_t type);
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static void cubic_conn_init(struct cc_var *ccv);
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static int cubic_mod_init(void);
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static void cubic_post_recovery(struct cc_var *ccv);
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static void cubic_record_rtt(struct cc_var *ccv);
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static void cubic_ssthresh_update(struct cc_var *ccv);
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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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/* Number of congestion events. */
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uint32_t num_cong_events;
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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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/* Time of last congestion event in ticks. */
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int t_last_cong;
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};
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MALLOC_DECLARE(M_CUBIC);
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MALLOC_DEFINE(M_CUBIC, "cubic data",
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"Per connection data required for the CUBIC congestion control algorithm");
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struct cc_algo cubic_cc_algo = {
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.name = "cubic",
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.ack_received = cubic_ack_received,
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.cb_destroy = cubic_cb_destroy,
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.cb_init = cubic_cb_init,
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.cong_signal = cubic_cong_signal,
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.conn_init = cubic_conn_init,
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.mod_init = cubic_mod_init,
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.post_recovery = cubic_post_recovery,
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};
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static void
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cubic_ack_received(struct cc_var *ccv, uint16_t type)
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{
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struct cubic *cubic_data;
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unsigned long w_tf, w_cubic_next;
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int ticks_since_cong;
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cubic_data = ccv->cc_data;
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cubic_record_rtt(ccv);
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/*
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* Regular ACK and we're not in cong/fast recovery and we're cwnd
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* limited and we're either not doing ABC or are slow starting or are
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* doing ABC and we've sent a cwnd's worth of bytes.
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*/
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if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
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(ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
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CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
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(V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
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/* Use the logic in NewReno ack_received() for slow start. */
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if (CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
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cubic_data->min_rtt_ticks == TCPTV_SRTTBASE)
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newreno_cc_algo.ack_received(ccv, type);
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else {
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ticks_since_cong = ticks - cubic_data->t_last_cong;
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/*
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* The mean RTT is used to best reflect the equations in
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* the I-D. Using min_rtt in the tf_cwnd calculation
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* causes w_tf to grow much faster than it should if the
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* RTT is dominated by network buffering rather than
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* propogation delay.
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*/
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w_tf = tf_cwnd(ticks_since_cong,
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cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
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CCV(ccv, t_maxseg));
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w_cubic_next = cubic_cwnd(ticks_since_cong +
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cubic_data->mean_rtt_ticks, cubic_data->max_cwnd,
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CCV(ccv, t_maxseg), cubic_data->K);
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ccv->flags &= ~CCF_ABC_SENTAWND;
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if (w_cubic_next < w_tf)
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/*
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* TCP-friendly region, follow tf
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* cwnd growth.
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*/
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CCV(ccv, snd_cwnd) = w_tf;
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else if (CCV(ccv, snd_cwnd) < w_cubic_next) {
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/*
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* Concave or convex region, follow CUBIC
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* cwnd growth.
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*/
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if (V_tcp_do_rfc3465)
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CCV(ccv, snd_cwnd) = w_cubic_next;
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else
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CCV(ccv, snd_cwnd) += ((w_cubic_next -
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CCV(ccv, snd_cwnd)) *
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CCV(ccv, t_maxseg)) /
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CCV(ccv, snd_cwnd);
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}
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/*
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* If we're not in slow start and we're probing for a
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* new cwnd limit at the start of a connection
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* (happens when hostcache has a relevant entry),
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* keep updating our current estimate of the
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* max_cwnd.
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*/
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if (cubic_data->num_cong_events == 0 &&
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cubic_data->max_cwnd < CCV(ccv, snd_cwnd))
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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}
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}
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}
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static void
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cubic_cb_destroy(struct cc_var *ccv)
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{
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if (ccv->cc_data != NULL)
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free(ccv->cc_data, M_CUBIC);
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}
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static int
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cubic_cb_init(struct cc_var *ccv)
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{
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struct cubic *cubic_data;
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cubic_data = malloc(sizeof(struct cubic), M_CUBIC, M_NOWAIT|M_ZERO);
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if (cubic_data == NULL)
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return (ENOMEM);
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/* Init some key variables with sensible defaults. */
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cubic_data->t_last_cong = ticks;
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cubic_data->min_rtt_ticks = TCPTV_SRTTBASE;
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cubic_data->mean_rtt_ticks = TCPTV_SRTTBASE;
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ccv->cc_data = cubic_data;
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return (0);
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}
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/*
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* Perform any necessary tasks before we enter congestion recovery.
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*/
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static void
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cubic_cong_signal(struct cc_var *ccv, uint32_t type)
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{
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struct cubic *cubic_data;
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cubic_data = ccv->cc_data;
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switch (type) {
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case CC_NDUPACK:
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if (!IN_FASTRECOVERY(CCV(ccv, t_flags))) {
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if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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cubic_ssthresh_update(ccv);
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cubic_data->num_cong_events++;
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cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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}
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ENTER_RECOVERY(CCV(ccv, t_flags));
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}
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break;
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case CC_ECN:
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if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
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cubic_ssthresh_update(ccv);
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cubic_data->num_cong_events++;
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cubic_data->prev_max_cwnd = cubic_data->max_cwnd;
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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cubic_data->t_last_cong = ticks;
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CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
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ENTER_CONGRECOVERY(CCV(ccv, t_flags));
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}
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break;
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case CC_RTO:
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/*
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* Grab the current time and record it so we know when the
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* most recent congestion event was. Only record it when the
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* timeout has fired more than once, as there is a reasonable
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* chance the first one is a false alarm and may not indicate
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* congestion.
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*/
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if (CCV(ccv, t_rxtshift) >= 2)
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cubic_data->num_cong_events++;
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cubic_data->t_last_cong = ticks;
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break;
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}
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}
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static void
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cubic_conn_init(struct cc_var *ccv)
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{
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struct cubic *cubic_data;
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cubic_data = ccv->cc_data;
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/*
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* Ensure we have a sane initial value for max_cwnd recorded. Without
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* this here bad things happen when entries from the TCP hostcache
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* get used.
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*/
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cubic_data->max_cwnd = CCV(ccv, snd_cwnd);
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}
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static int
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cubic_mod_init(void)
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{
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cubic_cc_algo.after_idle = newreno_cc_algo.after_idle;
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return (0);
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}
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/*
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* Perform any necessary tasks before we exit congestion recovery.
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*/
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static void
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cubic_post_recovery(struct cc_var *ccv)
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{
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struct cubic *cubic_data;
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cubic_data = ccv->cc_data;
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/* Fast convergence heuristic. */
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if (cubic_data->max_cwnd < cubic_data->prev_max_cwnd)
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cubic_data->max_cwnd = (cubic_data->max_cwnd * CUBIC_FC_FACTOR)
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>> CUBIC_SHIFT;
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if (IN_FASTRECOVERY(CCV(ccv, t_flags))) {
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/*
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* If inflight data is less than ssthresh, set cwnd
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* conservatively to avoid a burst of data, as suggested in
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* the NewReno RFC. Otherwise, use the CUBIC method.
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*
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* XXXLAS: Find a way to do this without needing curack
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*/
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if (SEQ_GT(ccv->curack + CCV(ccv, snd_ssthresh),
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CCV(ccv, snd_max)))
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CCV(ccv, snd_cwnd) = CCV(ccv, snd_max) - ccv->curack +
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CCV(ccv, t_maxseg);
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else
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/* Update cwnd based on beta and adjusted max_cwnd. */
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CCV(ccv, snd_cwnd) = max(1, ((CUBIC_BETA *
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cubic_data->max_cwnd) >> CUBIC_SHIFT));
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}
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cubic_data->t_last_cong = ticks;
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/* Calculate the average RTT between congestion epochs. */
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if (cubic_data->epoch_ack_count > 0 && cubic_data->sum_rtt_ticks > 0)
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cubic_data->mean_rtt_ticks = (int)(cubic_data->sum_rtt_ticks /
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cubic_data->epoch_ack_count);
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else
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/* For safety. */
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cubic_data->mean_rtt_ticks = cubic_data->min_rtt_ticks;
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cubic_data->epoch_ack_count = 0;
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cubic_data->sum_rtt_ticks = 0;
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cubic_data->K = cubic_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
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}
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/*
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* Record the min RTT and sum samples for the epoch average RTT calculation.
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*/
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static void
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cubic_record_rtt(struct cc_var *ccv)
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{
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struct cubic *cubic_data;
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int t_srtt_ticks;
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/* Ignore srtt until a min number of samples have been taken. */
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if (CCV(ccv, t_rttupdated) >= CUBIC_MIN_RTT_SAMPLES) {
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cubic_data = ccv->cc_data;
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t_srtt_ticks = CCV(ccv, t_srtt) / TCP_RTT_SCALE;
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/*
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* Record the current SRTT as our minrtt if it's the smallest
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* we've seen or minrtt is currently equal to its initialised
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* value.
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*
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* XXXLAS: Should there be some hysteresis for minrtt?
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*/
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if ((t_srtt_ticks < cubic_data->min_rtt_ticks ||
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cubic_data->min_rtt_ticks == TCPTV_SRTTBASE))
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cubic_data->min_rtt_ticks = max(1, t_srtt_ticks);
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/* Sum samples for epoch average RTT calculation. */
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cubic_data->sum_rtt_ticks += t_srtt_ticks;
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cubic_data->epoch_ack_count++;
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}
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}
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|
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/*
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* Update the ssthresh in the event of congestion.
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*/
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static void
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cubic_ssthresh_update(struct cc_var *ccv)
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{
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struct cubic *cubic_data;
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cubic_data = ccv->cc_data;
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/*
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* On the first congestion event, set ssthresh to cwnd * 0.5, on
|
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* subsequent congestion events, set it to cwnd * beta.
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*/
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if (cubic_data->num_cong_events == 0)
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CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd) >> 1;
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else
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CCV(ccv, snd_ssthresh) = (CCV(ccv, snd_cwnd) * CUBIC_BETA)
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>> CUBIC_SHIFT;
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}
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DECLARE_CC_MODULE(cubic, &cubic_cc_algo);
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229
sys/netinet/cc/cc_cubic.h
Normal file
229
sys/netinet/cc/cc_cubic.h
Normal file
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|
@ -0,0 +1,229 @@
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/*-
|
||||
* 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_ */
|
||||
Loading…
Reference in a new issue