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sys/netinet/cc/cc_cubic_8312bis.c

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/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* 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 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 <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#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 <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_cubic_8312bis.h>
#include <netinet/cc/cc_module.h>
static void cubic_8312bis_ack_received(struct cc_var *ccv, uint16_t type);
static void cubic_8312bis_cb_destroy(struct cc_var *ccv);
static int cubic_8312bis_cb_init(struct cc_var *ccv);
static void cubic_8312bis_cong_signal(struct cc_var *ccv, uint32_t type);
static void cubic_8312bis_conn_init(struct cc_var *ccv);
static int cubic_8312bis_mod_init(void);
static void cubic_8312bis_post_recovery(struct cc_var *ccv);
static void cubic_8312bis_record_rtt(struct cc_var *ccv);
static void cubic_8312bis_ssthresh_update(struct cc_var *ccv, uint32_t maxseg);
static void cubic_8312bis_after_idle(struct cc_var *ccv);
struct cubic_8312bis {
/* 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_8312bis_cc_algo = {
.name = "cubic_8312bis",
.ack_received = cubic_8312bis_ack_received,
.cb_destroy = cubic_8312bis_cb_destroy,
.cb_init = cubic_8312bis_cb_init,
.cong_signal = cubic_8312bis_cong_signal,
.conn_init = cubic_8312bis_conn_init,
.mod_init = cubic_8312bis_mod_init,
.post_recovery = cubic_8312bis_post_recovery,
.after_idle = cubic_8312bis_after_idle,
};
static void
cubic_8312bis_ack_received(struct cc_var *ccv, uint16_t type)
{
struct cubic_8312bis *cubic_data;
unsigned long w_tf, w_cubic_next;
int ticks_since_cong;
cubic_data = ccv->cc_data;
cubic_8312bis_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->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_8312bis_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_8312bis_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_8312bis_after_idle(struct cc_var *ccv)
{
struct cubic_8312bis *cubic_data;
cubic_data = ccv->cc_data;
cubic_data->max_cwnd = ulmax(cubic_data->max_cwnd, CCV(ccv, snd_cwnd));
cubic_data->K = cubic_8312bis_k(cubic_data->max_cwnd / CCV(ccv, t_maxseg));
newreno_cc_algo.after_idle(ccv);
cubic_data->t_last_cong = ticks;
}
static void
cubic_8312bis_cb_destroy(struct cc_var *ccv)
{
free(ccv->cc_data, M_CUBIC);
}
static int
cubic_8312bis_cb_init(struct cc_var *ccv)
{
struct cubic_8312bis *cubic_data;
cubic_data = malloc(sizeof(struct cubic_8312bis), 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_8312bis_cong_signal(struct cc_var *ccv, uint32_t type)
{
struct cubic_8312bis *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_8312bis_ssthresh_update(ccv, mss);
cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->t_last_cong = ticks;
cubic_data->K = cubic_8312bis_k(cubic_data->max_cwnd / mss);
}
ENTER_RECOVERY(CCV(ccv, t_flags));
}
break;
case CC_ECN:
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_8312bis_ssthresh_update(ccv, mss);
cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->t_last_cong = ticks;
cubic_data->K = cubic_8312bis_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_8312bis_k(cubic_data->max_cwnd / mss);
break;
}
}
static void
cubic_8312bis_conn_init(struct cc_var *ccv)
{
struct cubic_8312bis *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_8312bis_mod_init(void)
{
return (0);
}
/*
* Perform any necessary tasks before we exit congestion recovery.
*/
static void
cubic_8312bis_post_recovery(struct cc_var *ccv)
{
struct cubic_8312bis *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_8312bis_record_rtt(struct cc_var *ccv)
{
struct cubic_8312bis *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_8312bis_ssthresh_update(struct cc_var *ccv, uint32_t maxseg)
{
struct cubic_8312bis *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_8312bis, &cubic_8312bis_cc_algo);
MODULE_VERSION(cubic_8312bis, 1);