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freebsd/sys/netinet/cc/cc_htcp.c
Randall Stewart b8d60729de tcp: Congestion control cleanup. 
NOTE: HEADS UP read the note below if your kernel config is not including GENERIC!!

This patch does a bit of cleanup on TCP congestion control modules. There were some rather
interesting surprises that one could get i.e. where you use a socket option to change
from one CC (say cc_cubic) to another CC (say cc_vegas) and you could in theory get
a memory failure and end up on cc_newreno. This is not what one would expect. The
new code fixes this by requiring a cc_data_sz() function so we can malloc with M_WAITOK
and pass in to the init function preallocated memory. The CC init is expected in this
case *not* to fail but if it does and a module does break the
"no fail with memory given" contract we do fall back to the CC that was in place at the time.

This also fixes up a set of common newreno utilities that can be shared amongst other
CC modules instead of the other CC modules reaching into newreno and executing
what they think is a "common and understood" function. Lets put these functions in
cc.c and that way we have a common place that is easily findable by future developers or
bug fixers. This also allows newreno to evolve and grow support for its features i.e. ABE
and HYSTART++ without having to dance through hoops for other CC modules, instead
both newreno and the other modules just call into the common functions if they desire
that behavior or roll there own if that makes more sense.

Note: This commit changes the kernel configuration!! If you are not using GENERIC in
some form you must add a CC module option (one of CC_NEWRENO, CC_VEGAS, CC_CUBIC,
CC_CDG, CC_CHD, CC_DCTCP, CC_HTCP, CC_HD). You can have more than one defined
as well if you desire. Note that if you create a kernel configuration that does not
define a congestion control module and includes INET or INET6 the kernel compile will
break. Also you need to define a default, generic adds 'options CC_DEFAULT=\"newreno\"
but you can specify any string that represents the name of the CC module (same names
that show up in the CC module list under net.inet.tcp.cc). If you fail to add the
options CC_DEFAULT in your kernel configuration the kernel build will also break.

Reviewed by: Michael Tuexen
Sponsored by: Netflix Inc.
RELNOTES:YES
Differential Revision: https://reviews.freebsd.org/D32693
2021-11-11 06:28:18 -05:00

548 lines
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/*-
* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
*
* Copyright (c) 2007-2008
* Swinburne University of Technology, Melbourne, Australia
* Copyright (c) 2009-2010 Lawrence Stewart <lstewart@freebsd.org>
* Copyright (c) 2010 The FreeBSD Foundation
* All rights reserved.
*
* This software was developed at the Centre for Advanced Internet
* Architectures, Swinburne University of Technology, by Lawrence Stewart and
* James Healy, 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 H-TCP congestion control algorithm for FreeBSD,
* based on the Internet Draft "draft-leith-tcp-htcp-06.txt" by Leith and
* Shorten. 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 <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/cc/cc.h>
#include <netinet/cc/cc_module.h>
/* Fixed point math shifts. */
#define HTCP_SHIFT 8
#define HTCP_ALPHA_INC_SHIFT 4
#define HTCP_INIT_ALPHA 1
#define HTCP_DELTA_L hz /* 1 sec in ticks. */
#define HTCP_MINBETA 128 /* 0.5 << HTCP_SHIFT. */
#define HTCP_MAXBETA 204 /* ~0.8 << HTCP_SHIFT. */
#define HTCP_MINROWE 26 /* ~0.1 << HTCP_SHIFT. */
#define HTCP_MAXROWE 512 /* 2 << HTCP_SHIFT. */
/* RTT_ref (ms) used in the calculation of alpha if RTT scaling is enabled. */
#define HTCP_RTT_REF 100
/* Don't trust SRTT until this many samples have been taken. */
#define HTCP_MIN_RTT_SAMPLES 8
/*
* HTCP_CALC_ALPHA performs a fixed point math calculation to determine the
* value of alpha, based on the function defined in the HTCP spec.
*
* i.e. 1 + 10(delta - delta_l) + ((delta - delta_l) / 2) ^ 2
*
* "diff" is passed in to the macro as "delta - delta_l" and is expected to be
* in units of ticks.
*
* The joyousnous of fixed point maths means our function implementation looks a
* little funky...
*
* In order to maintain some precision in the calculations, a fixed point shift
* HTCP_ALPHA_INC_SHIFT is used to ensure the integer divisions don't
* truncate the results too badly.
*
* The "16" value is the "1" term in the alpha function shifted up by
* HTCP_ALPHA_INC_SHIFT
*
* The "160" value is the "10" multiplier in the alpha function multiplied by
* 2^HTCP_ALPHA_INC_SHIFT
*
* Specifying these as constants reduces the computations required. After
* up-shifting all the terms in the function and performing the required
* calculations, we down-shift the final result by HTCP_ALPHA_INC_SHIFT to
* ensure it is back in the correct range.
*
* The "hz" terms are required as kernels can be configured to run with
* different tick timers, which we have to adjust for in the alpha calculation
* (which originally was defined in terms of seconds).
*
* We also have to be careful to constrain the value of diff such that it won't
* overflow whilst performing the calculation. The middle term i.e. (160 * diff)
* / hz is the limiting factor in the calculation. We must constrain diff to be
* less than the max size of an int divided by the constant 160 figure
* i.e. diff < INT_MAX / 160
*
* NB: Changing HTCP_ALPHA_INC_SHIFT will require you to MANUALLY update the
* constants used in this function!
*/
#define HTCP_CALC_ALPHA(diff) \
((\
(16) + \
((160 * (diff)) / hz) + \
(((diff) / hz) * (((diff) << HTCP_ALPHA_INC_SHIFT) / (4 * hz))) \
) >> HTCP_ALPHA_INC_SHIFT)
static void htcp_ack_received(struct cc_var *ccv, uint16_t type);
static void htcp_cb_destroy(struct cc_var *ccv);
static int htcp_cb_init(struct cc_var *ccv, void *ptr);
static void htcp_cong_signal(struct cc_var *ccv, uint32_t type);
static int htcp_mod_init(void);
static void htcp_post_recovery(struct cc_var *ccv);
static void htcp_recalc_alpha(struct cc_var *ccv);
static void htcp_recalc_beta(struct cc_var *ccv);
static void htcp_record_rtt(struct cc_var *ccv);
static void htcp_ssthresh_update(struct cc_var *ccv);
static size_t htcp_data_sz(void);
struct htcp {
/* cwnd before entering cong recovery. */
unsigned long prev_cwnd;
/* cwnd additive increase parameter. */
int alpha;
/* cwnd multiplicative decrease parameter. */
int beta;
/* Largest rtt seen for the flow. */
int maxrtt;
/* Shortest rtt seen for the flow. */
int minrtt;
/* Time of last congestion event in ticks. */
int t_last_cong;
};
static int htcp_rtt_ref;
/*
* The maximum number of ticks the value of diff can reach in
* htcp_recalc_alpha() before alpha will stop increasing due to overflow.
* See comment above HTCP_CALC_ALPHA for more info.
*/
static int htcp_max_diff = INT_MAX / ((1 << HTCP_ALPHA_INC_SHIFT) * 10);
/* Per-netstack vars. */
VNET_DEFINE_STATIC(u_int, htcp_adaptive_backoff) = 0;
VNET_DEFINE_STATIC(u_int, htcp_rtt_scaling) = 0;
#define V_htcp_adaptive_backoff VNET(htcp_adaptive_backoff)
#define V_htcp_rtt_scaling VNET(htcp_rtt_scaling)
struct cc_algo htcp_cc_algo = {
.name = "htcp",
.ack_received = htcp_ack_received,
.cb_destroy = htcp_cb_destroy,
.cb_init = htcp_cb_init,
.cong_signal = htcp_cong_signal,
.mod_init = htcp_mod_init,
.post_recovery = htcp_post_recovery,
.cc_data_sz = htcp_data_sz,
.after_idle = newreno_cc_after_idle,
};
static void
htcp_ack_received(struct cc_var *ccv, uint16_t type)
{
struct htcp *htcp_data;
htcp_data = ccv->cc_data;
htcp_record_rtt(ccv);
/*
* Regular ACK and we're not in cong/fast recovery and we're cwnd
* limited and we're either not doing ABC or are slow starting or are
* doing ABC and we've sent a cwnd's worth of bytes.
*/
if (type == CC_ACK && !IN_RECOVERY(CCV(ccv, t_flags)) &&
(ccv->flags & CCF_CWND_LIMITED) && (!V_tcp_do_rfc3465 ||
CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh) ||
(V_tcp_do_rfc3465 && ccv->flags & CCF_ABC_SENTAWND))) {
htcp_recalc_beta(ccv);
htcp_recalc_alpha(ccv);
/*
* Use the logic in NewReno ack_received() for slow start and
* for the first HTCP_DELTA_L ticks after either the flow starts
* or a congestion event (when alpha equals 1).
*/
if (htcp_data->alpha == 1 ||
CCV(ccv, snd_cwnd) <= CCV(ccv, snd_ssthresh))
newreno_cc_ack_received(ccv, type);
else {
if (V_tcp_do_rfc3465) {
/* Increment cwnd by alpha segments. */
CCV(ccv, snd_cwnd) += htcp_data->alpha *
CCV(ccv, t_maxseg);
ccv->flags &= ~CCF_ABC_SENTAWND;
} else
/*
* Increment cwnd by alpha/cwnd segments to
* approximate an increase of alpha segments
* per RTT.
*/
CCV(ccv, snd_cwnd) += (((htcp_data->alpha <<
HTCP_SHIFT) / (CCV(ccv, snd_cwnd) /
CCV(ccv, t_maxseg))) * CCV(ccv, t_maxseg))
>> HTCP_SHIFT;
}
}
}
static void
htcp_cb_destroy(struct cc_var *ccv)
{
free(ccv->cc_data, M_CC_MEM);
}
static size_t
htcp_data_sz(void)
{
return(sizeof(struct htcp));
}
static int
htcp_cb_init(struct cc_var *ccv, void *ptr)
{
struct htcp *htcp_data;
INP_WLOCK_ASSERT(ccv->ccvc.tcp->t_inpcb);
if (ptr == NULL) {
htcp_data = malloc(sizeof(struct htcp), M_CC_MEM, M_NOWAIT);
if (htcp_data == NULL)
return (ENOMEM);
} else
htcp_data = ptr;
/* Init some key variables with sensible defaults. */
htcp_data->alpha = HTCP_INIT_ALPHA;
htcp_data->beta = HTCP_MINBETA;
htcp_data->maxrtt = TCPTV_SRTTBASE;
htcp_data->minrtt = TCPTV_SRTTBASE;
htcp_data->prev_cwnd = 0;
htcp_data->t_last_cong = ticks;
ccv->cc_data = htcp_data;
return (0);
}
/*
* Perform any necessary tasks before we enter congestion recovery.
*/
static void
htcp_cong_signal(struct cc_var *ccv, uint32_t type)
{
struct htcp *htcp_data;
u_int mss;
htcp_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))) {
/*
* Apply hysteresis to maxrtt to ensure
* reductions in the RTT are reflected in our
* measurements.
*/
htcp_data->maxrtt = (htcp_data->minrtt +
(htcp_data->maxrtt - htcp_data->minrtt) *
95) / 100;
htcp_ssthresh_update(ccv);
htcp_data->t_last_cong = ticks;
htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
}
ENTER_RECOVERY(CCV(ccv, t_flags));
}
break;
case CC_ECN:
if (!IN_CONGRECOVERY(CCV(ccv, t_flags))) {
/*
* Apply hysteresis to maxrtt to ensure reductions in
* the RTT are reflected in our measurements.
*/
htcp_data->maxrtt = (htcp_data->minrtt + (htcp_data->maxrtt -
htcp_data->minrtt) * 95) / 100;
htcp_ssthresh_update(ccv);
CCV(ccv, snd_cwnd) = CCV(ccv, snd_ssthresh);
htcp_data->t_last_cong = ticks;
htcp_data->prev_cwnd = CCV(ccv, snd_cwnd);
ENTER_CONGRECOVERY(CCV(ccv, t_flags));
}
break;
case CC_RTO:
CCV(ccv, snd_ssthresh) = max(min(CCV(ccv, snd_wnd),
CCV(ccv, snd_cwnd)) / 2 / mss,
2) * mss;
CCV(ccv, snd_cwnd) = mss;
/*
* Grab the current time and record it so we know when the
* most recent congestion event was. Only record it when the
* timeout has fired more than once, as there is a reasonable
* chance the first one is a false alarm and may not indicate
* congestion.
*/
if (CCV(ccv, t_rxtshift) >= 2)
htcp_data->t_last_cong = ticks;
break;
}
}
static int
htcp_mod_init(void)
{
/*
* HTCP_RTT_REF is defined in ms, and t_srtt in the tcpcb is stored in
* units of TCP_RTT_SCALE*hz. Scale HTCP_RTT_REF to be in the same units
* as t_srtt.
*/
htcp_rtt_ref = (HTCP_RTT_REF * TCP_RTT_SCALE * hz) / 1000;
return (0);
}
/*
* Perform any necessary tasks before we exit congestion recovery.
*/
static void
htcp_post_recovery(struct cc_var *ccv)
{
int pipe;
struct htcp *htcp_data;
pipe = 0;
htcp_data = ccv->cc_data;
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 HTCP method.
*
* XXXLAS: Find a way to do this without needing curack
*/
if (V_tcp_do_newsack)
pipe = tcp_compute_pipe(ccv->ccvc.tcp);
else
pipe = CCV(ccv, snd_max) - ccv->curack;
if (pipe < CCV(ccv, snd_ssthresh))
/*
* Ensure that cwnd down not collape to 1 MSS under
* adverse conditions. Implements RFC6582
*/
CCV(ccv, snd_cwnd) = max(pipe, CCV(ccv, t_maxseg)) +
CCV(ccv, t_maxseg);
else
CCV(ccv, snd_cwnd) = max(1, ((htcp_data->beta *
htcp_data->prev_cwnd / CCV(ccv, t_maxseg))
>> HTCP_SHIFT)) * CCV(ccv, t_maxseg);
}
}
static void
htcp_recalc_alpha(struct cc_var *ccv)
{
struct htcp *htcp_data;
int alpha, diff, now;
htcp_data = ccv->cc_data;
now = ticks;
/*
* If ticks has wrapped around (will happen approximately once every 49
* days on a machine with the default kern.hz=1000) and a flow straddles
* the wrap point, our alpha calcs will be completely wrong. We cut our
* losses and restart alpha from scratch by setting t_last_cong = now -
* HTCP_DELTA_L.
*
* This does not deflate our cwnd at all. It simply slows the rate cwnd
* is growing by until alpha regains the value it held prior to taking
* this drastic measure.
*/
if (now < htcp_data->t_last_cong)
htcp_data->t_last_cong = now - HTCP_DELTA_L;
diff = now - htcp_data->t_last_cong - HTCP_DELTA_L;
/* Cap alpha if the value of diff would overflow HTCP_CALC_ALPHA(). */
if (diff < htcp_max_diff) {
/*
* If it has been more than HTCP_DELTA_L ticks since congestion,
* increase alpha according to the function defined in the spec.
*/
if (diff > 0) {
alpha = HTCP_CALC_ALPHA(diff);
/*
* Adaptive backoff fairness adjustment:
* 2 * (1 - beta) * alpha_raw
*/
if (V_htcp_adaptive_backoff)
alpha = max(1, (2 * ((1 << HTCP_SHIFT) -
htcp_data->beta) * alpha) >> HTCP_SHIFT);
/*
* RTT scaling: (RTT / RTT_ref) * alpha
* alpha will be the raw value from HTCP_CALC_ALPHA() if
* adaptive backoff is off, or the adjusted value if
* adaptive backoff is on.
*/
if (V_htcp_rtt_scaling)
alpha = max(1, (min(max(HTCP_MINROWE,
(CCV(ccv, t_srtt) << HTCP_SHIFT) /
htcp_rtt_ref), HTCP_MAXROWE) * alpha)
>> HTCP_SHIFT);
} else
alpha = 1;
htcp_data->alpha = alpha;
}
}
static void
htcp_recalc_beta(struct cc_var *ccv)
{
struct htcp *htcp_data;
htcp_data = ccv->cc_data;
/*
* TCPTV_SRTTBASE is the initialised value of each connection's SRTT, so
* we only calc beta if the connection's SRTT has been changed from its
* initial value. beta is bounded to ensure it is always between
* HTCP_MINBETA and HTCP_MAXBETA.
*/
if (V_htcp_adaptive_backoff && htcp_data->minrtt != TCPTV_SRTTBASE &&
htcp_data->maxrtt != TCPTV_SRTTBASE)
htcp_data->beta = min(max(HTCP_MINBETA,
(htcp_data->minrtt << HTCP_SHIFT) / htcp_data->maxrtt),
HTCP_MAXBETA);
else
htcp_data->beta = HTCP_MINBETA;
}
/*
* Record the minimum and maximum RTT seen for the connection. These are used in
* the calculation of beta if adaptive backoff is enabled.
*/
static void
htcp_record_rtt(struct cc_var *ccv)
{
struct htcp *htcp_data;
htcp_data = ccv->cc_data;
/* XXXLAS: Should there be some hysteresis for minrtt? */
/*
* Record the current SRTT as our minrtt if it's the smallest we've seen
* or minrtt is currently equal to its initialised value. Ignore SRTT
* until a min number of samples have been taken.
*/
if ((CCV(ccv, t_srtt) < htcp_data->minrtt ||
htcp_data->minrtt == TCPTV_SRTTBASE) &&
(CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES))
htcp_data->minrtt = CCV(ccv, t_srtt);
/*
* Record the current SRTT as our maxrtt if it's the largest we've
* seen. Ignore SRTT until a min number of samples have been taken.
*/
if (CCV(ccv, t_srtt) > htcp_data->maxrtt
&& CCV(ccv, t_rttupdated) >= HTCP_MIN_RTT_SAMPLES)
htcp_data->maxrtt = CCV(ccv, t_srtt);
}
/*
* Update the ssthresh in the event of congestion.
*/
static void
htcp_ssthresh_update(struct cc_var *ccv)
{
struct htcp *htcp_data;
htcp_data = ccv->cc_data;
/*
* On the first congestion event, set ssthresh to cwnd * 0.5, on
* subsequent congestion events, set it to cwnd * beta.
*/
if (CCV(ccv, snd_ssthresh) == TCP_MAXWIN << TCP_MAX_WINSHIFT)
CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
HTCP_MINBETA) >> HTCP_SHIFT;
else {
htcp_recalc_beta(ccv);
CCV(ccv, snd_ssthresh) = ((u_long)CCV(ccv, snd_cwnd) *
htcp_data->beta) >> HTCP_SHIFT;
}
}
SYSCTL_DECL(_net_inet_tcp_cc_htcp);
SYSCTL_NODE(_net_inet_tcp_cc, OID_AUTO, htcp, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
"H-TCP related settings");
SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, adaptive_backoff,
CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_adaptive_backoff), 0,
"enable H-TCP adaptive backoff");
SYSCTL_UINT(_net_inet_tcp_cc_htcp, OID_AUTO, rtt_scaling,
CTLFLAG_VNET | CTLFLAG_RW, &VNET_NAME(htcp_rtt_scaling), 0,
"enable H-TCP RTT scaling");
DECLARE_CC_MODULE(htcp, &htcp_cc_algo);
MODULE_VERSION(htcp, 2);
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