hardenedbsd/HardenedBSD
1
0
Fork 0
mirror of https://git.hardenedbsd.org/hardenedbsd/HardenedBSD.git synced 2024-11-22 20:11:06 +01:00
Code Issues Actions Packages Projects Releases Wiki Activity
a64729f507
HardenedBSD/sys/netinet/cc/cc_cubic.c
Cheng Cui ee45061051
cc_cubic: use newreno to emulate AIMD in TCP-friendly region 
Reviewed by: rscheff, tuexen
Differential Revision: https://reviews.freebsd.org/D46546
2024-09-17 10:37:00 -04:00

741 lines
23 KiB
C
Raw Blame History

/*-
* SPDX-License-Identifier: BSD-2-Clause
*
* 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/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 <net/route.h>
#include <net/route/nhop.h>
#include <netinet/in_pcb.h>
#include <netinet/tcp.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_hpts.h>
#include <netinet/cc/cc.h>
#include <netinet/cc/cc_cubic.h>
#include <netinet/cc/cc_module.h>
static void cubic_ack_received(struct cc_var *ccv, ccsignal_t type);
static void cubic_cb_destroy(struct cc_var *ccv);
static int cubic_cb_init(struct cc_var *ccv, void *ptr);
static void cubic_cong_signal(struct cc_var *ccv, ccsignal_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);
static size_t cubic_data_sz(void);
static void cubic_newround(struct cc_var *ccv, uint32_t round_cnt);
static void cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt,
uint32_t rxtcnt, uint32_t fas);
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,
.cc_data_sz = cubic_data_sz,
.rttsample = cubic_rttsample,
.newround = cubic_newround
};
static void
cubic_log_hystart_event(struct cc_var *ccv, struct cubic *cubicd, uint8_t mod, uint32_t flex1)
{
/*
* Types of logs (mod value)
* 1 - rtt_thresh in flex1, checking to see if RTT is to great.
* 2 - rtt is too great, rtt_thresh in flex1.
* 3 - CSS is active incr in flex1
* 4 - A new round is beginning flex1 is round count
* 5 - A new RTT measurement flex1 is the new measurement.
* 6 - We enter CA ssthresh is also in flex1.
* 7 - Socket option to change hystart executed opt.val in flex1.
* 8 - Back out of CSS into SS, flex1 is the css_baseline_minrtt
* 9 - We enter CA, via an ECN mark.
* 10 - We enter CA, via a loss.
* 11 - We have slipped out of SS into CA via cwnd growth.
* 12 - After idle has re-enabled hystart++
*/
struct tcpcb *tp;
if (hystart_bblogs == 0)
return;
tp = ccv->tp;
if (tcp_bblogging_on(tp)) {
union tcp_log_stackspecific log;
struct timeval tv;
memset(&log, 0, sizeof(log));
log.u_bbr.flex1 = flex1;
log.u_bbr.flex2 = cubicd->css_current_round_minrtt;
log.u_bbr.flex3 = cubicd->css_lastround_minrtt;
log.u_bbr.flex4 = cubicd->css_rttsample_count;
log.u_bbr.flex5 = cubicd->css_entered_at_round;
log.u_bbr.flex6 = cubicd->css_baseline_minrtt;
/* We only need bottom 16 bits of flags */
log.u_bbr.flex7 = cubicd->flags & 0x0000ffff;
log.u_bbr.flex8 = mod;
log.u_bbr.epoch = cubicd->css_current_round;
log.u_bbr.timeStamp = tcp_get_usecs(&tv);
log.u_bbr.lt_epoch = cubicd->css_fas_at_css_entry;
log.u_bbr.pkts_out = cubicd->css_last_fas;
log.u_bbr.delivered = cubicd->css_lowrtt_fas;
log.u_bbr.pkt_epoch = ccv->flags;
TCP_LOG_EVENTP(tp, NULL,
&tptosocket(tp)->so_rcv,
&tptosocket(tp)->so_snd,
TCP_HYSTART, 0,
0, &log, false, &tv);
}
}
static void
cubic_does_slow_start(struct cc_var *ccv, struct cubic *cubicd)
{
/*
* In slow-start with ABC enabled and no RTO in sight?
* (Must not use abc_l_var > 1 if slow starting after
* an RTO. On RTO, snd_nxt = snd_una, so the
* snd_nxt == snd_max check is sufficient to
* handle this).
*
* XXXLAS: Find a way to signal SS after RTO that
* doesn't rely on tcpcb vars.
*/
u_int cw = CCV(ccv, snd_cwnd);
u_int incr = CCV(ccv, t_maxseg);
uint16_t abc_val;
cubicd->flags |= CUBICFLAG_IN_SLOWSTART;
if (ccv->flags & CCF_USE_LOCAL_ABC)
abc_val = ccv->labc;
else
abc_val = V_tcp_abc_l_var;
if ((ccv->flags & CCF_HYSTART_ALLOWED) &&
(cubicd->flags & CUBICFLAG_HYSTART_ENABLED) &&
((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) == 0)) {
/*
* Hystart is allowed and still enabled and we are not yet
* in CSS. Lets check to see if we can make a decision on
* if we need to go into CSS.
*/
if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) &&
(cubicd->css_current_round_minrtt != 0xffffffff) &&
(cubicd->css_lastround_minrtt != 0xffffffff)) {
uint32_t rtt_thresh;
/* Clamp (minrtt_thresh, lastround/8, maxrtt_thresh) */
rtt_thresh = (cubicd->css_lastround_minrtt >> 3);
if (rtt_thresh < hystart_minrtt_thresh)
rtt_thresh = hystart_minrtt_thresh;
if (rtt_thresh > hystart_maxrtt_thresh)
rtt_thresh = hystart_maxrtt_thresh;
cubic_log_hystart_event(ccv, cubicd, 1, rtt_thresh);
if (cubicd->css_current_round_minrtt >= (cubicd->css_lastround_minrtt + rtt_thresh)) {
/* Enter CSS */
cubicd->flags |= CUBICFLAG_HYSTART_IN_CSS;
cubicd->css_fas_at_css_entry = cubicd->css_lowrtt_fas;
/*
* The draft (v4) calls for us to set baseline to css_current_round_min
* but that can cause an oscillation. We probably shoudl be using
* css_lastround_minrtt, but the authors insist that will cause
* issues on exiting early. We will leave the draft version for now
* but I suspect this is incorrect.
*/
cubicd->css_baseline_minrtt = cubicd->css_current_round_minrtt;
cubicd->css_entered_at_round = cubicd->css_current_round;
cubic_log_hystart_event(ccv, cubicd, 2, rtt_thresh);
}
}
}
if (CCV(ccv, snd_nxt) == CCV(ccv, snd_max))
incr = min(ccv->bytes_this_ack,
ccv->nsegs * abc_val *
CCV(ccv, t_maxseg));
else
incr = min(ccv->bytes_this_ack, CCV(ccv, t_maxseg));
/* Only if Hystart is enabled will the flag get set */
if (cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) {
incr /= hystart_css_growth_div;
cubic_log_hystart_event(ccv, cubicd, 3, incr);
}
/* ABC is on by default, so incr equals 0 frequently. */
if (incr > 0)
CCV(ccv, snd_cwnd) = min((cw + incr),
TCP_MAXWIN << CCV(ccv, snd_scale));
}
static void
cubic_ack_received(struct cc_var *ccv, ccsignal_t type)
{
struct cubic *cubic_data;
unsigned long W_est, W_cubic;
int usecs_since_epoch;
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_usecs == TCPTV_SRTTBASE) {
cubic_does_slow_start(ccv, cubic_data);
} else {
if (cubic_data->flags & CUBICFLAG_HYSTART_IN_CSS) {
/*
* We have slipped into CA with
* CSS active. Deactivate all.
*/
/* Turn off the CSS flag */
cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
/* Disable use of CSS in the future except long idle */
cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED;
cubic_log_hystart_event(ccv, cubic_data, 11, CCV(ccv, snd_ssthresh));
}
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->W_max = CCV(ccv, snd_cwnd);
cubic_data->t_epoch = 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_epoch = ticks;
cubic_data->K = cubic_k(cubic_data->W_max /
CCV(ccv, t_maxseg));
}
usecs_since_epoch = (ticks - cubic_data->t_epoch) * tick;
if (usecs_since_epoch < 0) {
/*
* dragging t_epoch along
*/
usecs_since_epoch = INT_MAX;
cubic_data->t_epoch = ticks - INT_MAX;
}
W_est = tf_cwnd(ccv);
/*
* The mean RTT is used to best reflect the equations in
* the I-D.
*/
W_cubic = cubic_cwnd(usecs_since_epoch +
cubic_data->mean_rtt_usecs,
cubic_data->W_max,
CCV(ccv, t_maxseg),
cubic_data->K);
if (W_cubic < W_est) {
/*
* TCP-friendly region, follow tf
* cwnd growth.
*/
CCV(ccv, snd_cwnd) = ulmin(W_est, INT_MAX);
cubic_data->flags |= CUBICFLAG_IN_TF;
} else if (CCV(ccv, snd_cwnd) < W_cubic) {
/*
* Concave or convex region, follow CUBIC
* cwnd growth.
* Only update snd_cwnd, if it doesn't shrink.
*/
CCV(ccv, snd_cwnd) = ulmin(W_cubic, INT_MAX);
cubic_data->flags &= ~CUBICFLAG_IN_TF;
}
/*
* 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
* W_max.
*/
if (((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) &&
cubic_data->W_max < CCV(ccv, snd_cwnd)) {
cubic_data->W_max = CCV(ccv, snd_cwnd);
cubic_data->K = cubic_k(cubic_data->W_max /
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_epoch.
*/
static void
cubic_after_idle(struct cc_var *ccv)
{
struct cubic *cubic_data;
cubic_data = ccv->cc_data;
cubic_data->W_max = ulmax(cubic_data->W_max, CCV(ccv, snd_cwnd));
cubic_data->K = cubic_k(cubic_data->W_max / CCV(ccv, t_maxseg));
if ((cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) == 0) {
/*
* Re-enable hystart if we have been idle.
*/
cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
cubic_data->flags |= CUBICFLAG_HYSTART_ENABLED;
cubic_log_hystart_event(ccv, cubic_data, 12, CCV(ccv, snd_ssthresh));
}
newreno_cc_after_idle(ccv);
cubic_data->t_epoch = ticks;
}
static void
cubic_cb_destroy(struct cc_var *ccv)
{
free(ccv->cc_data, M_CC_MEM);
}
static size_t
cubic_data_sz(void)
{
return (sizeof(struct cubic));
}
static int
cubic_cb_init(struct cc_var *ccv, void *ptr)
{
struct cubic *cubic_data;
INP_WLOCK_ASSERT(tptoinpcb(ccv->tp));
if (ptr == NULL) {
cubic_data = malloc(sizeof(struct cubic), M_CC_MEM, M_NOWAIT|M_ZERO);
if (cubic_data == NULL)
return (ENOMEM);
} else
cubic_data = ptr;
/* Init some key variables with sensible defaults. */
cubic_data->t_epoch = ticks;
cubic_data->min_rtt_usecs = TCPTV_SRTTBASE;
cubic_data->mean_rtt_usecs = 1;
ccv->cc_data = cubic_data;
cubic_data->flags = CUBICFLAG_HYSTART_ENABLED;
/* At init set both to infinity */
cubic_data->css_lastround_minrtt = 0xffffffff;
cubic_data->css_current_round_minrtt = 0xffffffff;
cubic_data->css_current_round = 0;
cubic_data->css_baseline_minrtt = 0xffffffff;
cubic_data->css_rttsample_count = 0;
cubic_data->css_entered_at_round = 0;
cubic_data->css_fas_at_css_entry = 0;
cubic_data->css_lowrtt_fas = 0;
cubic_data->css_last_fas = 0;
return (0);
}
/*
* Perform any necessary tasks before we enter congestion recovery.
*/
static void
cubic_cong_signal(struct cc_var *ccv, ccsignal_t type)
{
struct cubic *cubic_data;
uint32_t mss, pipe;
cubic_data = ccv->cc_data;
mss = tcp_fixed_maxseg(ccv->tp);
switch (type) {
case CC_NDUPACK:
if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) {
/* Make sure the flags are all off we had a loss */
cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED;
cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
cubic_log_hystart_event(ccv, cubic_data, 10, CCV(ccv, snd_ssthresh));
}
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_epoch = ticks;
cubic_data->K = cubic_k(cubic_data->W_max / mss);
}
ENTER_RECOVERY(CCV(ccv, t_flags));
}
break;
case CC_ECN:
if (cubic_data->flags & CUBICFLAG_HYSTART_ENABLED) {
/* Make sure the flags are all off we had a loss */
cubic_data->flags &= ~CUBICFLAG_HYSTART_ENABLED;
cubic_data->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
cubic_log_hystart_event(ccv, cubic_data, 9, CCV(ccv, snd_ssthresh));
}
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
cubic_ssthresh_update(ccv, mss);
cubic_data->flags |= CUBICFLAG_CONG_EVENT;
cubic_data->t_epoch = ticks;
cubic_data->K = cubic_k(cubic_data->W_max / 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) {
/*
* Remember the state only for the first RTO event. This
* will help us restore the state to the values seen
* at the most recent congestion avoidance stage before
* the current RTO event.
*/
cubic_data->undo_t_epoch = cubic_data->t_epoch;
cubic_data->undo_cwnd_epoch = cubic_data->cwnd_epoch;
cubic_data->undo_W_est = cubic_data->W_est;
cubic_data->undo_cwnd_prior = cubic_data->cwnd_prior;
cubic_data->undo_W_max = cubic_data->W_max;
cubic_data->undo_K = cubic_data->K;
if (V_tcp_do_newsack) {
pipe = tcp_compute_pipe(ccv->tp);
} else {
pipe = CCV(ccv, snd_max) -
CCV(ccv, snd_fack) +
CCV(ccv, sackhint.sack_bytes_rexmit);
}
CCV(ccv, snd_ssthresh) = max(2,
(((uint64_t)min(CCV(ccv, snd_wnd), pipe) *
CUBIC_BETA) >> CUBIC_SHIFT) / mss) * mss;
}
cubic_data->flags |= CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT;
cubic_data->undo_W_max = cubic_data->W_max;
CCV(ccv, snd_cwnd) = mss;
break;
case CC_RTO_ERR:
cubic_data->flags &= ~(CUBICFLAG_CONG_EVENT | CUBICFLAG_RTO_EVENT);
cubic_data->K = cubic_data->undo_K;
cubic_data->cwnd_prior = cubic_data->undo_cwnd_prior;
cubic_data->W_max = cubic_data->undo_W_max;
cubic_data->W_est = cubic_data->undo_W_est;
cubic_data->cwnd_epoch = cubic_data->undo_cwnd_epoch;
cubic_data->t_epoch = cubic_data->undo_t_epoch;
break;
default:
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 W_max recorded. Without
* this here bad things happen when entries from the TCP hostcache
* get used.
*/
cubic_data->W_max = 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_newsack)
pipe = tcp_compute_pipe(ccv->tp);
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 W_max. */
CCV(ccv, snd_cwnd) = max(((uint64_t)cubic_data->W_max *
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_usecs >= cubic_data->epoch_ack_count) {
cubic_data->mean_rtt_usecs = (int)(cubic_data->sum_rtt_usecs /
cubic_data->epoch_ack_count);
}
cubic_data->epoch_ack_count = 0;
cubic_data->sum_rtt_usecs = 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;
uint32_t t_srtt_usecs;
/* 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_usecs = tcp_get_srtt(ccv->tp,
TCP_TMR_GRANULARITY_USEC);
/*
* 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_usecs < cubic_data->min_rtt_usecs ||
cubic_data->min_rtt_usecs == TCPTV_SRTTBASE)) {
/* A minimal rtt is a single unshifted tick of a ticks
* timer. */
cubic_data->min_rtt_usecs = max(tick >> TCP_RTT_SHIFT,
t_srtt_usecs);
/*
* If the connection is within its first congestion
* epoch, ensure we prime mean_rtt_usecs with a
* reasonable value until the epoch average RTT is
* calculated in cubic_post_recovery().
*/
if (cubic_data->min_rtt_usecs >
cubic_data->mean_rtt_usecs)
cubic_data->mean_rtt_usecs =
cubic_data->min_rtt_usecs;
}
/* Sum samples for epoch average RTT calculation. */
cubic_data->sum_rtt_usecs += t_srtt_usecs;
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->W_max) {
cwnd = ((uint64_t)cwnd * CUBIC_FC_FACTOR) >> CUBIC_SHIFT;
}
cubic_data->undo_W_max = cubic_data->W_max;
cubic_data->W_max = cwnd;
if (cubic_data->flags & CUBICFLAG_IN_TF) {
/* If in the TCP friendly region, follow what newreno does */
ssthresh = newreno_cc_cwnd_on_multiplicative_decrease(ccv, maxseg);
} else if ((cubic_data->flags & CUBICFLAG_CONG_EVENT) == 0) {
/*
* On the first congestion event, set ssthresh to cwnd * 0.5
* and reduce W_max to cwnd * beta. This aligns the cubic
* concave region appropriately.
*/
ssthresh = cwnd >> 1;
cubic_data->W_max = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT;
} else {
/*
* On subsequent congestion events, set ssthresh to cwnd * beta.
*/
ssthresh = ((uint64_t)cwnd * CUBIC_BETA) >> CUBIC_SHIFT;
}
CCV(ccv, snd_ssthresh) = max(ssthresh, 2 * maxseg);
}
static void
cubic_rttsample(struct cc_var *ccv, uint32_t usec_rtt, uint32_t rxtcnt, uint32_t fas)
{
struct cubic *cubicd;
cubicd = ccv->cc_data;
if (rxtcnt > 1) {
/*
* Only look at RTT's that are non-ambiguous.
*/
return;
}
cubicd->css_rttsample_count++;
cubicd->css_last_fas = fas;
if (cubicd->css_current_round_minrtt > usec_rtt) {
cubicd->css_current_round_minrtt = usec_rtt;
cubicd->css_lowrtt_fas = cubicd->css_last_fas;
}
if ((cubicd->css_rttsample_count >= hystart_n_rttsamples) &&
(cubicd->css_current_round_minrtt != 0xffffffff) &&
(cubicd->css_current_round_minrtt < cubicd->css_baseline_minrtt) &&
(cubicd->css_lastround_minrtt != 0xffffffff)) {
/*
* We were in CSS and the RTT is now less, we
* entered CSS erroneously.
*/
cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
cubic_log_hystart_event(ccv, cubicd, 8, cubicd->css_baseline_minrtt);
cubicd->css_baseline_minrtt = 0xffffffff;
}
if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED)
cubic_log_hystart_event(ccv, cubicd, 5, usec_rtt);
}
static void
cubic_newround(struct cc_var *ccv, uint32_t round_cnt)
{
struct cubic *cubicd;
cubicd = ccv->cc_data;
/* We have entered a new round */
cubicd->css_lastround_minrtt = cubicd->css_current_round_minrtt;
cubicd->css_current_round_minrtt = 0xffffffff;
cubicd->css_rttsample_count = 0;
cubicd->css_current_round = round_cnt;
if ((cubicd->flags & CUBICFLAG_HYSTART_IN_CSS) &&
((round_cnt - cubicd->css_entered_at_round) >= hystart_css_rounds)) {
/* Enter CA */
if (ccv->flags & CCF_HYSTART_CAN_SH_CWND) {
/*
* We engage more than snd_ssthresh, engage
* the brakes!! Though we will stay in SS to
* creep back up again, so lets leave CSS active
* and give us hystart_css_rounds more rounds.
*/
if (ccv->flags & CCF_HYSTART_CONS_SSTH) {
CCV(ccv, snd_ssthresh) = ((cubicd->css_lowrtt_fas + cubicd->css_fas_at_css_entry) / 2);
} else {
CCV(ccv, snd_ssthresh) = cubicd->css_lowrtt_fas;
}
CCV(ccv, snd_cwnd) = cubicd->css_fas_at_css_entry;
cubicd->css_entered_at_round = round_cnt;
} else {
CCV(ccv, snd_ssthresh) = CCV(ccv, snd_cwnd);
/* Turn off the CSS flag */
cubicd->flags &= ~CUBICFLAG_HYSTART_IN_CSS;
/* Disable use of CSS in the future except long idle */
cubicd->flags &= ~CUBICFLAG_HYSTART_ENABLED;
}
cubic_log_hystart_event(ccv, cubicd, 6, CCV(ccv, snd_ssthresh));
}
if (cubicd->flags & CUBICFLAG_HYSTART_ENABLED)
cubic_log_hystart_event(ccv, cubicd, 4, round_cnt);
}
DECLARE_CC_MODULE(cubic, &cubic_cc_algo);
MODULE_VERSION(cubic, 2);
Reference in New Issue View Git Blame Copy Permalink