/* $NetBSD: tcp_congctl.c,v 1.29 2024/05/14 19:00:44 andvar Exp $ */
/*-
* Copyright (c) 1997, 1998, 1999, 2001, 2005, 2006 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Jason R. Thorpe and Kevin M. Lahey of the Numerical Aerospace Simulation
* Facility, NASA Ames Research Center.
* This code is derived from software contributed to The NetBSD Foundation
* by Charles M. Hannum.
* This code is derived from software contributed to The NetBSD Foundation
* by Rui Paulo.
*
* 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 NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
*/
/*
* Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
* All rights reserved.
*
* 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.
* 3. Neither the name of the project nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE PROJECT 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 PROJECT 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.
*/
/*
* @(#)COPYRIGHT 1.1 (NRL) 17 January 1995
*
* NRL grants permission for redistribution and use in source and binary
* forms, with or without modification, of the software and documentation
* created at NRL 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.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgements:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* This product includes software developed at the Information
* Technology Division, US Naval Research Laboratory.
* 4. Neither the name of the NRL nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THE SOFTWARE PROVIDED BY NRL IS PROVIDED BY NRL 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 NRL 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.
*
* The views and conclusions contained in the software and documentation
* are those of the authors and should not be interpreted as representing
* official policies, either expressed or implied, of the US Naval
* Research Laboratory (NRL).
*/
/*
* Copyright (c) 1982, 1986, 1988, 1990, 1993, 1994, 1995
* The Regents of the University of California. All rights reserved.
*
* 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.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS 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 REGENTS 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.
*
* @(#)tcp_input.c 8.12 (Berkeley) 5/24/95
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: tcp_congctl.c,v 1.29 2024/05/14 19:00:44 andvar Exp $");
#ifdef _KERNEL_OPT
#include "opt_inet.h"
#include "opt_tcp_debug.h"
#include "opt_tcp_congctl.h"
#endif
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/errno.h>
#include <sys/syslog.h>
#include <sys/pool.h>
#include <sys/domain.h>
#include <sys/kernel.h>
#include <sys/mutex.h>
#include <net/if.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/in6_var.h>
#include <netinet/icmp6.h>
#endif
#include <netinet/tcp.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_congctl.h>
#ifdef TCP_DEBUG
#include <netinet/tcp_debug.h>
#endif
/*
* TODO:
* consider separating the actual implementations in another file.
*/
static void tcp_common_congestion_exp(struct tcpcb *, int, int);
static int tcp_reno_do_fast_retransmit(struct tcpcb *, const struct tcphdr *);
static int tcp_reno_fast_retransmit(struct tcpcb *, const struct tcphdr *);
static void tcp_reno_slow_retransmit(struct tcpcb *);
static void tcp_reno_fast_retransmit_newack(struct tcpcb *,
const struct tcphdr *);
static void tcp_reno_newack(struct tcpcb *, const struct tcphdr *);
static void tcp_reno_congestion_exp(struct tcpcb *tp);
static int tcp_newreno_fast_retransmit(struct tcpcb *, const struct tcphdr *);
static void tcp_newreno_fast_retransmit_newack(struct tcpcb *,
const struct tcphdr *);
static void tcp_newreno_newack(struct tcpcb *, const struct tcphdr *);
static int tcp_cubic_fast_retransmit(struct tcpcb *, const struct tcphdr *);
static void tcp_cubic_slow_retransmit(struct tcpcb *tp);
static void tcp_cubic_newack(struct tcpcb *, const struct tcphdr *);
static void tcp_cubic_congestion_exp(struct tcpcb *);
static void tcp_congctl_fillnames(void);
extern int tcprexmtthresh;
MALLOC_DEFINE(M_TCPCONGCTL, "tcpcongctl", "TCP congestion control structures");
/* currently selected global congestion control */
char tcp_congctl_global_name[TCPCC_MAXLEN];
/* available global congestion control algorithms */
char tcp_congctl_avail[10 * TCPCC_MAXLEN];
/*
* Used to list the available congestion control algorithms.
*/
TAILQ_HEAD(, tcp_congctlent) tcp_congctlhd =
TAILQ_HEAD_INITIALIZER(tcp_congctlhd);
static struct tcp_congctlent * tcp_congctl_global;
static kmutex_t tcp_congctl_mtx;
void
tcp_congctl_init(void)
{
int r __diagused;
mutex_init(&tcp_congctl_mtx, MUTEX_DEFAULT, IPL_NONE);
/* Base algorithms. */
r = tcp_congctl_register("reno", &tcp_reno_ctl);
KASSERT(r == 0);
r = tcp_congctl_register("newreno", &tcp_newreno_ctl);
KASSERT(r == 0);
r = tcp_congctl_register("cubic", &tcp_cubic_ctl);
KASSERT(r == 0);
/* NewReno is the default. */
#ifndef TCP_CONGCTL_DEFAULT
#define TCP_CONGCTL_DEFAULT "newreno"
#endif
r = tcp_congctl_select(NULL, TCP_CONGCTL_DEFAULT);
KASSERT(r == 0);
}
/*
* Register a congestion algorithm and select it if we have none.
*/
int
tcp_congctl_register(const char *name, const struct tcp_congctl *tcc)
{
struct tcp_congctlent *ntcc, *tccp;
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent)
if (!strcmp(name, tccp->congctl_name)) {
/* name already registered */
return EEXIST;
}
ntcc = malloc(sizeof(*ntcc), M_TCPCONGCTL, M_WAITOK|M_ZERO);
strlcpy(ntcc->congctl_name, name, sizeof(ntcc->congctl_name) - 1);
ntcc->congctl_ctl = tcc;
TAILQ_INSERT_TAIL(&tcp_congctlhd, ntcc, congctl_ent);
tcp_congctl_fillnames();
if (TAILQ_FIRST(&tcp_congctlhd) == ntcc)
tcp_congctl_select(NULL, name);
return 0;
}
int
tcp_congctl_unregister(const char *name)
{
struct tcp_congctlent *tccp, *rtccp;
unsigned int size;
rtccp = NULL;
size = 0;
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) {
if (!strcmp(name, tccp->congctl_name))
rtccp = tccp;
size++;
}
if (!rtccp)
return ENOENT;
if (size <= 1 || tcp_congctl_global == rtccp || rtccp->congctl_refcnt)
return EBUSY;
TAILQ_REMOVE(&tcp_congctlhd, rtccp, congctl_ent);
free(rtccp, M_TCPCONGCTL);
tcp_congctl_fillnames();
return 0;
}
/*
* Select a congestion algorithm by name.
*/
int
tcp_congctl_select(struct tcpcb *tp, const char *name)
{
struct tcp_congctlent *tccp, *old_tccp, *new_tccp;
bool old_found, new_found;
KASSERT(name);
old_found = (tp == NULL || tp->t_congctl == NULL);
old_tccp = NULL;
new_found = false;
new_tccp = NULL;
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) {
if (!old_found && tccp->congctl_ctl == tp->t_congctl) {
old_tccp = tccp;
old_found = true;
}
if (!new_found && !strcmp(name, tccp->congctl_name)) {
new_tccp = tccp;
new_found = true;
}
if (new_found && old_found) {
if (tp) {
mutex_enter(&tcp_congctl_mtx);
if (old_tccp)
old_tccp->congctl_refcnt--;
tp->t_congctl = new_tccp->congctl_ctl;
new_tccp->congctl_refcnt++;
mutex_exit(&tcp_congctl_mtx);
} else {
tcp_congctl_global = new_tccp;
strlcpy(tcp_congctl_global_name,
new_tccp->congctl_name,
sizeof(tcp_congctl_global_name) - 1);
}
return 0;
}
}
return EINVAL;
}
void
tcp_congctl_release(struct tcpcb *tp)
{
struct tcp_congctlent *tccp;
KASSERT(tp->t_congctl);
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) {
if (tccp->congctl_ctl == tp->t_congctl) {
tccp->congctl_refcnt--;
return;
}
}
}
/*
* Returns the name of a congestion algorithm.
*/
const char *
tcp_congctl_bystruct(const struct tcp_congctl *tcc)
{
struct tcp_congctlent *tccp;
KASSERT(tcc);
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent)
if (tccp->congctl_ctl == tcc)
return tccp->congctl_name;
return NULL;
}
static void
tcp_congctl_fillnames(void)
{
struct tcp_congctlent *tccp;
const char *delim = " ";
tcp_congctl_avail[0] = '\0';
TAILQ_FOREACH(tccp, &tcp_congctlhd, congctl_ent) {
strlcat(tcp_congctl_avail, tccp->congctl_name,
sizeof(tcp_congctl_avail) - 1);
if (TAILQ_NEXT(tccp, congctl_ent))
strlcat(tcp_congctl_avail, delim,
sizeof(tcp_congctl_avail) - 1);
}
}
/* ------------------------------------------------------------------------ */
/*
* Common stuff
*/
/* Window reduction (1-beta) for [New]Reno: 0.5 */
#define RENO_BETAA 1
#define RENO_BETAB 2
/* Window reduction (1-beta) for Cubic: 0.8 */
#define CUBIC_BETAA 4
#define CUBIC_BETAB 5
/* Draft Rhee Section 4.1 */
#define CUBIC_CA 4
#define CUBIC_CB 10
static void
tcp_common_congestion_exp(struct tcpcb *tp, int betaa, int betab)
{
u_long win;
/*
* Reduce the congestion window and the slow start threshold.
*/
win = ulmin(tp->snd_wnd, tp->snd_cwnd) * betaa / betab / tp->t_segsz;
if (win < 2)
win = 2;
tp->snd_ssthresh = win * tp->t_segsz;
tp->snd_recover = tp->snd_max;
tp->snd_cwnd = tp->snd_ssthresh;
/*
* When using TCP ECN, notify the peer that
* we reduced the cwnd.
*/
if (TCP_ECN_ALLOWED(tp))
tp->t_flags |= TF_ECN_SND_CWR;
}
/* ------------------------------------------------------------------------ */
/*
* TCP/Reno congestion control.
*/
static void
tcp_reno_congestion_exp(struct tcpcb *tp)
{
tcp_common_congestion_exp(tp, RENO_BETAA, RENO_BETAB);
}
static int
tcp_reno_do_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th)
{
/*
* Dup acks mean that packets have left the
* network (they're now cached at the receiver)
* so bump cwnd by the amount in the receiver
* to keep a constant cwnd packets in the
* network.
*
* If we are using TCP/SACK, then enter
* Fast Recovery if the receiver SACKs
* data that is tcprexmtthresh * MSS
* bytes past the last ACKed segment,
* irrespective of the number of DupAcks.
*/
tcp_seq onxt = tp->snd_nxt;
tp->t_partialacks = 0;
TCP_TIMER_DISARM(tp, TCPT_REXMT);
tp->t_rtttime = 0;
if (TCP_SACK_ENABLED(tp)) {
tp->t_dupacks = tcprexmtthresh;
tp->sack_newdata = tp->snd_nxt;
tp->snd_cwnd = tp->t_segsz;
(void) tcp_output(tp);
return 0;
}
tp->snd_nxt = th->th_ack;
tp->snd_cwnd = tp->t_segsz;
(void) tcp_output(tp);
tp->snd_cwnd = tp->snd_ssthresh + tp->t_segsz * tp->t_dupacks;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
return 0;
}
static int
tcp_reno_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th)
{
/*
* We know we're losing at the current
* window size so do congestion avoidance
* (set ssthresh to half the current window
* and pull our congestion window back to
* the new ssthresh).
*/
tcp_reno_congestion_exp(tp);
return tcp_reno_do_fast_retransmit(tp, th);
}
static void
tcp_reno_slow_retransmit(struct tcpcb *tp)
{
u_long win;
/*
* Close the congestion window down to one segment
* (we'll open it by one segment for each ack we get).
* Since we probably have a window's worth of unacked
* data accumulated, this "slow start" keeps us from
* dumping all that data as back-to-back packets (which
* might overwhelm an intermediate gateway).
*
* There are two phases to the opening: Initially we
* open by one mss on each ack. This makes the window
* size increase exponentially with time. If the
* window is larger than the path can handle, this
* exponential growth results in dropped packet(s)
* almost immediately. To get more time between
* drops but still "push" the network to take advantage
* of improving conditions, we switch from exponential
* to linear window opening at some threshold size.
* For a threshold, we use half the current window
* size, truncated to a multiple of the mss.
*
* (the minimum cwnd that will give us exponential
* growth is 2 mss. We don't allow the threshold
* to go below this.)
*/
win = ulmin(tp->snd_wnd, tp->snd_cwnd) / 2 / tp->t_segsz;
if (win < 2)
win = 2;
/* Loss Window MUST be one segment. */
tp->snd_cwnd = tp->t_segsz;
tp->snd_ssthresh = win * tp->t_segsz;
tp->t_partialacks = -1;
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
if (TCP_ECN_ALLOWED(tp))
tp->t_flags |= TF_ECN_SND_CWR;
}
static void
tcp_reno_fast_retransmit_newack(struct tcpcb *tp,
const struct tcphdr *th)
{
if (tp->t_partialacks < 0) {
/*
* We were not in fast recovery. Reset the duplicate ack
* counter.
*/
tp->t_dupacks = 0;
} else {
/*
* Clamp the congestion window to the crossover point and
* exit fast recovery.
*/
if (tp->snd_cwnd > tp->snd_ssthresh)
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_partialacks = -1;
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
if (TCP_SACK_ENABLED(tp) && SEQ_GT(th->th_ack, tp->snd_fack))
tp->snd_fack = th->th_ack;
}
}
static void
tcp_reno_newack(struct tcpcb *tp, const struct tcphdr *th)
{
/*
* When new data is acked, open the congestion window.
*/
u_int cw = tp->snd_cwnd;
u_int incr = tp->t_segsz;
if (tcp_do_abc) {
/*
* RFC 3465 Appropriate Byte Counting (ABC)
*/
int acked = th->th_ack - tp->snd_una;
if (cw >= tp->snd_ssthresh) {
tp->t_bytes_acked += acked;
if (tp->t_bytes_acked >= cw) {
/* Time to increase the window. */
tp->t_bytes_acked -= cw;
} else {
/* No need to increase yet. */
incr = 0;
}
} else {
/*
* use 2*SMSS or 1*SMSS for the "L" param,
* depending on sysctl setting.
*
* (See RFC 3465 2.3 Choosing the Limit)
*/
u_int abc_lim;
abc_lim = (tcp_abc_aggressive == 0 ||
tp->snd_nxt != tp->snd_max) ? incr : incr * 2;
incr = uimin(acked, abc_lim);
}
} else {
/*
* If the window gives us less than ssthresh packets
* in flight, open exponentially (segsz per packet).
* Otherwise open linearly: segsz per window
* (segsz^2 / cwnd per packet).
*/
if (cw >= tp->snd_ssthresh) {
incr = incr * incr / cw;
}
}
tp->snd_cwnd = uimin(cw + incr, TCP_MAXWIN << tp->snd_scale);
}
const struct tcp_congctl tcp_reno_ctl = {
.fast_retransmit = tcp_reno_fast_retransmit,
.slow_retransmit = tcp_reno_slow_retransmit,
.fast_retransmit_newack = tcp_reno_fast_retransmit_newack,
.newack = tcp_reno_newack,
.cong_exp = tcp_reno_congestion_exp,
};
/*
* TCP/NewReno Congestion control.
*/
static int
tcp_newreno_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th)
{
if (SEQ_LT(th->th_ack, tp->snd_high)) {
/*
* False fast retransmit after timeout.
* Do not enter fast recovery
*/
tp->t_dupacks = 0;
return 1;
}
/*
* Fast retransmit is same as reno.
*/
return tcp_reno_fast_retransmit(tp, th);
}
/*
* Implement the NewReno response to a new ack, checking for partial acks in
* fast recovery.
*/
static void
tcp_newreno_fast_retransmit_newack(struct tcpcb *tp, const struct tcphdr *th)
{
if (tp->t_partialacks < 0) {
/*
* We were not in fast recovery. Reset the duplicate ack
* counter.
*/
tp->t_dupacks = 0;
} else if (SEQ_LT(th->th_ack, tp->snd_recover)) {
/*
* This is a partial ack. Retransmit the first unacknowledged
* segment and deflate the congestion window by the amount of
* acknowledged data. Do not exit fast recovery.
*/
tcp_seq onxt = tp->snd_nxt;
u_long ocwnd = tp->snd_cwnd;
int sack_num_segs = 1, sack_bytes_rxmt = 0;
/*
* snd_una has not yet been updated and the socket's send
* buffer has not yet drained off the ACK'd data, so we
* have to leave snd_una as it was to get the correct data
* offset in tcp_output().
*/
tp->t_partialacks++;
TCP_TIMER_DISARM(tp, TCPT_REXMT);
tp->t_rtttime = 0;
if (TCP_SACK_ENABLED(tp)) {
/*
* Partial ack handling within a sack recovery episode.
* Keeping this very simple for now. When a partial ack
* is received, force snd_cwnd to a value that will
* allow the sender to transmit no more than 2 segments.
* If necessary, a fancier scheme can be adopted at a
* later point, but for now, the goal is to prevent the
* sender from bursting a large amount of data in the
* midst of sack recovery.
*/
/*
* send one or 2 segments based on how much
* new data was acked
*/
if (((th->th_ack - tp->snd_una) / tp->t_segsz) > 2)
sack_num_segs = 2;
(void)tcp_sack_output(tp, &sack_bytes_rxmt);
tp->snd_cwnd = sack_bytes_rxmt +
(tp->snd_nxt - tp->sack_newdata) +
sack_num_segs * tp->t_segsz;
tp->t_flags |= TF_ACKNOW;
(void) tcp_output(tp);
} else {
tp->snd_nxt = th->th_ack;
/*
* Set snd_cwnd to one segment beyond ACK'd offset
* snd_una is not yet updated when we're called
*/
tp->snd_cwnd = tp->t_segsz + (th->th_ack - tp->snd_una);
(void) tcp_output(tp);
tp->snd_cwnd = ocwnd;
if (SEQ_GT(onxt, tp->snd_nxt))
tp->snd_nxt = onxt;
/*
* Partial window deflation. Relies on fact that
* tp->snd_una not updated yet.
*/
tp->snd_cwnd -= (th->th_ack - tp->snd_una -
tp->t_segsz);
}
} else {
/*
* Complete ack. Inflate the congestion window to ssthresh
* and exit fast recovery.
*
* Window inflation should have left us with approx.
* snd_ssthresh outstanding data. But in case we
* would be inclined to send a burst, better to do
* it via the slow start mechanism.
*/
if (SEQ_SUB(tp->snd_max, th->th_ack) < tp->snd_ssthresh)
tp->snd_cwnd = SEQ_SUB(tp->snd_max, th->th_ack)
+ tp->t_segsz;
else
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_partialacks = -1;
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
if (TCP_SACK_ENABLED(tp) && SEQ_GT(th->th_ack, tp->snd_fack))
tp->snd_fack = th->th_ack;
}
}
static void
tcp_newreno_newack(struct tcpcb *tp, const struct tcphdr *th)
{
/*
* If we are still in fast recovery (meaning we are using
* NewReno and we have only received partial acks), do not
* inflate the window yet.
*/
if (tp->t_partialacks < 0)
tcp_reno_newack(tp, th);
}
const struct tcp_congctl tcp_newreno_ctl = {
.fast_retransmit = tcp_newreno_fast_retransmit,
.slow_retransmit = tcp_reno_slow_retransmit,
.fast_retransmit_newack = tcp_newreno_fast_retransmit_newack,
.newack = tcp_newreno_newack,
.cong_exp = tcp_reno_congestion_exp,
};
/*
* CUBIC -
http://tools.ietf.org/html/draft-rhee-tcpm-cubic-02
*/
/* Cubic prototypes */
static void tcp_cubic_update_ctime(struct tcpcb *tp);
static uint32_t tcp_cubic_diff_ctime(struct tcpcb *);
static uint32_t tcp_cubic_cbrt(uint32_t);
static ulong tcp_cubic_getW(struct tcpcb *, uint32_t, uint32_t);
/* Cubic TIME functions - XXX I don't like using timevals and microuptime */
/*
* Set congestion timer to now
*/
static void
tcp_cubic_update_ctime(struct tcpcb *tp)
{
struct timeval now_timeval;
getmicrouptime(&now_timeval);
tp->snd_cubic_ctime = now_timeval.tv_sec * 1000 +
now_timeval.tv_usec / 1000;
}
/*
* milliseconds from last congestion
*/
static uint32_t
tcp_cubic_diff_ctime(struct tcpcb *tp)
{
struct timeval now_timeval;
getmicrouptime(&now_timeval);
return now_timeval.tv_sec * 1000 + now_timeval.tv_usec / 1000 -
tp->snd_cubic_ctime;
}
/*
* Approximate cubic root
*/
#define CBRT_ROUNDS 30
static uint32_t
tcp_cubic_cbrt(uint32_t v)
{
int i, rounds = CBRT_ROUNDS;
uint64_t x = v / 3;
/* We fail to calculate correct for small numbers */
if (v == 0)
return 0;
else if (v < 4)
return 1;
/*
* largest x that 2*x^3+3*x fits 64bit
* Avoid overflow for a time cost
*/
if (x > 2097151)
rounds += 10;
for (i = 0; i < rounds; i++)
if (rounds == CBRT_ROUNDS)
x = (v + 2 * x * x * x) / (3 * x * x);
else
/* Avoid overflow */
x = v / (3 * x * x) + 2 * x / 3;
return (uint32_t)x;
}
/* Draft Rhee Section 3.1 - get W(t+rtt) - Eq. 1 */
static ulong
tcp_cubic_getW(struct tcpcb *tp, uint32_t ms_elapsed, uint32_t rtt)
{
uint32_t K;
long tK3;
/* Section 3.1 Eq. 2 */
K = tcp_cubic_cbrt(tp->snd_cubic_wmax / CUBIC_BETAB *
CUBIC_CB / CUBIC_CA);
/* (t-K)^3 - not clear why is the measure unit mattering */
tK3 = (long)(ms_elapsed + rtt) - (long)K;
tK3 = tK3 * tK3 * tK3;
return CUBIC_CA * tK3 / CUBIC_CB + tp->snd_cubic_wmax;
}
static void
tcp_cubic_congestion_exp(struct tcpcb *tp)
{
/*
* Congestion - Set WMax and shrink cwnd
*/
tcp_cubic_update_ctime(tp);
/* Section 3.6 - Fast Convergence */
if (tp->snd_cubic_wmax < tp->snd_cubic_wmax_last) {
tp->snd_cubic_wmax_last = tp->snd_cubic_wmax;
tp->snd_cubic_wmax = tp->snd_cubic_wmax / 2 +
tp->snd_cubic_wmax * CUBIC_BETAA / CUBIC_BETAB / 2;
} else {
tp->snd_cubic_wmax_last = tp->snd_cubic_wmax;
tp->snd_cubic_wmax = tp->snd_cwnd;
}
tp->snd_cubic_wmax = uimax(tp->t_segsz, tp->snd_cubic_wmax);
/* Shrink CWND */
tcp_common_congestion_exp(tp, CUBIC_BETAA, CUBIC_BETAB);
}
static int
tcp_cubic_fast_retransmit(struct tcpcb *tp, const struct tcphdr *th)
{
if (SEQ_LT(th->th_ack, tp->snd_high)) {
/* See newreno */
tp->t_dupacks = 0;
return 1;
}
/*
* mark WMax
*/
tcp_cubic_congestion_exp(tp);
/* Do fast retransmit */
return tcp_reno_do_fast_retransmit(tp, th);
}
static void
tcp_cubic_newack(struct tcpcb *tp, const struct tcphdr *th)
{
uint32_t ms_elapsed, rtt;
u_long w_tcp;
/* Congestion avoidance and not in fast recovery and usable rtt */
if (tp->snd_cwnd > tp->snd_ssthresh && tp->t_partialacks < 0 &&
/*
* t_srtt is 1/32 units of slow ticks
* converting it in ms would be equal to
* (t_srtt >> 5) * 1000 / PR_SLOWHZ ~= (t_srtt << 5) / PR_SLOWHZ
*/
(rtt = (tp->t_srtt << 5) / PR_SLOWHZ) > 0) {
ms_elapsed = tcp_cubic_diff_ctime(tp);
/* Compute W_tcp(t) */
w_tcp = tp->snd_cubic_wmax * CUBIC_BETAA / CUBIC_BETAB +
ms_elapsed / rtt / 3;
if (tp->snd_cwnd > w_tcp) {
/* Not in TCP friendly mode */
tp->snd_cwnd += (tcp_cubic_getW(tp, ms_elapsed, rtt) -
tp->snd_cwnd) / tp->snd_cwnd;
} else {
/* friendly TCP mode */
tp->snd_cwnd = w_tcp;
}
/* Make sure we are within limits */
tp->snd_cwnd = uimax(tp->snd_cwnd, tp->t_segsz);
tp->snd_cwnd = uimin(tp->snd_cwnd, TCP_MAXWIN << tp->snd_scale);
} else {
/* Use New Reno */
tcp_newreno_newack(tp, th);
}
}
static void
tcp_cubic_slow_retransmit(struct tcpcb *tp)
{
/* Timeout - Mark new congestion */
tcp_cubic_congestion_exp(tp);
/* Loss Window MUST be one segment. */
tp->snd_cwnd = tp->t_segsz;
tp->t_partialacks = -1;
tp->t_dupacks = 0;
tp->t_bytes_acked = 0;
if (TCP_ECN_ALLOWED(tp))
tp->t_flags |= TF_ECN_SND_CWR;
}
const struct tcp_congctl tcp_cubic_ctl = {
.fast_retransmit = tcp_cubic_fast_retransmit,
.slow_retransmit = tcp_cubic_slow_retransmit,
.fast_retransmit_newack = tcp_newreno_fast_retransmit_newack,
.newack = tcp_cubic_newack,
.cong_exp = tcp_cubic_congestion_exp,
};
