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/*
* Copyright (c) 2013-2014 Apple Inc. All rights reserved.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_START@
*
* This file contains Original Code and/or Modifications of Original Code
* as defined in and that are subject to the Apple Public Source License
* Version 2.0 (the 'License'). You may not use this file except in
* compliance with the License. The rights granted to you under the License
* may not be used to create, or enable the creation or redistribution of,
* unlawful or unlicensed copies of an Apple operating system, or to
* circumvent, violate, or enable the circumvention or violation of, any
* terms of an Apple operating system software license agreement.
*
* Please obtain a copy of the License at
* http://www.opensource.apple.com/apsl/ and read it before using this file.
*
* The Original Code and all software distributed under the License are
* distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
* Please see the License for the specific language governing rights and
* limitations under the License.
*
* @APPLE_OSREFERENCE_LICENSE_HEADER_END@
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/protosw.h>
#include <sys/socketvar.h>
#include <sys/syslog.h>
#include <net/route.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#if INET6
#include <netinet/ip6.h>
#endif /* INET6 */
#include <netinet/ip_var.h>
#include <netinet/tcp.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_cc.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_seq.h>
#include <kern/task.h>
#include <libkern/OSAtomic.h>
static int tcp_cubic_init(struct tcpcb *tp);
static int tcp_cubic_cleanup(struct tcpcb *tp);
static void tcp_cubic_cwnd_init_or_reset(struct tcpcb *tp);
static void tcp_cubic_congestion_avd(struct tcpcb *tp, struct tcphdr *th);
static void tcp_cubic_ack_rcvd(struct tcpcb *tp, struct tcphdr *th);
static void tcp_cubic_pre_fr(struct tcpcb *tp);
static void tcp_cubic_post_fr(struct tcpcb *tp, struct tcphdr *th);
static void tcp_cubic_after_timeout(struct tcpcb *tp);
static int tcp_cubic_delay_ack(struct tcpcb *tp, struct tcphdr *th);
static void tcp_cubic_switch_cc(struct tcpcb *tp, u_int16_t old_index);
static uint32_t tcp_cubic_update(struct tcpcb *tp, u_int32_t rtt);
static uint32_t tcp_cubic_tcpwin(struct tcpcb *tp, struct tcphdr *th);
static inline void tcp_cubic_clear_state(struct tcpcb *tp);
extern float cbrtf(float x);
struct tcp_cc_algo tcp_cc_cubic = {
.name = "cubic",
.init = tcp_cubic_init,
.cleanup = tcp_cubic_cleanup,
.cwnd_init = tcp_cubic_cwnd_init_or_reset,
.congestion_avd = tcp_cubic_congestion_avd,
.ack_rcvd = tcp_cubic_ack_rcvd,
.pre_fr = tcp_cubic_pre_fr,
.post_fr = tcp_cubic_post_fr,
.after_idle = tcp_cubic_cwnd_init_or_reset,
.after_timeout = tcp_cubic_after_timeout,
.delay_ack = tcp_cubic_delay_ack,
.switch_to = tcp_cubic_switch_cc
};
const float tcp_cubic_backoff = 0.2; /* multiplicative decrease factor */
const float tcp_cubic_coeff = 0.4;
const float tcp_cubic_fast_convergence_factor = 0.875;
SYSCTL_SKMEM_TCP_INT(OID_AUTO, cubic_tcp_friendliness, CTLFLAG_RW | CTLFLAG_LOCKED,
static int, tcp_cubic_tcp_friendliness, 0, "Enable TCP friendliness");
SYSCTL_SKMEM_TCP_INT(OID_AUTO, cubic_fast_convergence, CTLFLAG_RW | CTLFLAG_LOCKED,
static int, tcp_cubic_fast_convergence, 0, "Enable fast convergence");
SYSCTL_SKMEM_TCP_INT(OID_AUTO, cubic_use_minrtt, CTLFLAG_RW | CTLFLAG_LOCKED,
static int, tcp_cubic_use_minrtt, 0, "use a min of 5 sec rtt");
static int tcp_cubic_init(struct tcpcb *tp)
{
OSIncrementAtomic((volatile SInt32 *)&tcp_cc_cubic.num_sockets);
VERIFY(tp->t_ccstate != NULL);
tcp_cubic_clear_state(tp);
return (0);
}
static int tcp_cubic_cleanup(struct tcpcb *tp)
{
#pragma unused(tp)
OSDecrementAtomic((volatile SInt32 *)&tcp_cc_cubic.num_sockets);
return (0);
}
/*
* Initialize the congestion window at the beginning of a connection or
* after idle time
*/
static void tcp_cubic_cwnd_init_or_reset(struct tcpcb *tp)
{
VERIFY(tp->t_ccstate != NULL);
tcp_cubic_clear_state(tp);
tcp_cc_cwnd_init_or_reset(tp);
tp->t_pipeack = 0;
tcp_clear_pipeack_state(tp);
/* Start counting bytes for RFC 3465 again */
tp->t_bytes_acked = 0;
/*
* slow start threshold could get initialized to a lower value
* when there is a cached value in the route metrics. In this case,
* the connection can enter congestion avoidance without any packet
* loss and Cubic will enter steady-state too early. It is better
* to always probe to find the initial slow-start threshold.
*/
if (tp->t_inpcb->inp_stat->txbytes <= TCP_CC_CWND_INIT_BYTES
&& tp->snd_ssthresh < (TCP_MAXWIN << TCP_MAX_WINSHIFT))
tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
/* Initialize cubic last max to be same as ssthresh */
tp->t_ccstate->cub_last_max = tp->snd_ssthresh;
}
/*
* Compute the target congestion window for the next RTT according to
* cubic equation when an ack is received.
*
* W(t) = C(t-K)^3 + W(last_max)
*/
static uint32_t
tcp_cubic_update(struct tcpcb *tp, u_int32_t rtt)
{
float K, var;
u_int32_t elapsed_time, win;
win = min(tp->snd_cwnd, tp->snd_wnd);
if (tp->t_ccstate->cub_last_max == 0)
tp->t_ccstate->cub_last_max = tp->snd_ssthresh;
if (tp->t_ccstate->cub_epoch_start == 0) {
/*
* This is the beginning of a new epoch, initialize some of
* the variables that we need to use for computing the
* congestion window later.
*/
tp->t_ccstate->cub_epoch_start = tcp_now;
if (tp->t_ccstate->cub_epoch_start == 0)
tp->t_ccstate->cub_epoch_start = 1;
if (win < tp->t_ccstate->cub_last_max) {
VERIFY(current_task() == kernel_task);
/*
* Compute cubic epoch period, this is the time
* period that the window will take to increase to
* last_max again after backoff due to loss.
*/
K = (tp->t_ccstate->cub_last_max - win)
/ tp->t_maxseg / tcp_cubic_coeff;
K = cbrtf(K);
tp->t_ccstate->cub_epoch_period = K * TCP_RETRANSHZ;
/* Origin point */
tp->t_ccstate->cub_origin_point =
tp->t_ccstate->cub_last_max;
} else {
tp->t_ccstate->cub_epoch_period = 0;
tp->t_ccstate->cub_origin_point = win;
}
tp->t_ccstate->cub_target_win = 0;
}
VERIFY(tp->t_ccstate->cub_origin_point > 0);
/*
* Compute the target window for the next RTT using smoothed RTT
* as an estimate for next RTT.
*/
elapsed_time = timer_diff(tcp_now, 0,
tp->t_ccstate->cub_epoch_start, 0);
if (tcp_cubic_use_minrtt)
elapsed_time += max(tcp_cubic_use_minrtt, rtt);
else
elapsed_time += rtt;
var = (elapsed_time - tp->t_ccstate->cub_epoch_period) / TCP_RETRANSHZ;
var = var * var * var * (tcp_cubic_coeff * tp->t_maxseg);
tp->t_ccstate->cub_target_win = (u_int32_t)(tp->t_ccstate->cub_origin_point + var);
return (tp->t_ccstate->cub_target_win);
}
/*
* Standard TCP utilizes bandwidth well in low RTT and low BDP connections
* even when there is some packet loss. Enabling TCP mode will help Cubic
* to achieve this kind of utilization.
*
* But if there is a bottleneck link in the path with a fixed size queue
* and fixed bandwidth, TCP Cubic will help to reduce packet loss at this
* link because of the steady-state behavior. Using average and mean
* absolute deviation of W(lastmax), we try to detect if the congestion
* window is close to the bottleneck bandwidth. In that case, disabling
* TCP mode will help to minimize packet loss at this link.
*
* Disable TCP mode if the W(lastmax) (the window where previous packet
* loss happened) is within a small range from the average last max
* calculated.
*/
#define TCP_CUBIC_ENABLE_TCPMODE(_tp_) \
((!soissrcrealtime((_tp_)->t_inpcb->inp_socket) && \
(_tp_)->t_ccstate->cub_mean_dev > (tp->t_maxseg << 1)) ? 1 : 0)
/*
* Compute the window growth if standard TCP (AIMD) was used with
* a backoff of 0.5 and additive increase of 1 packet per RTT.
*
* TCP window at time t can be calculated using the following equation
* with beta as 0.8
*
* W(t) <- Wmax * beta + 3 * ((1 - beta)/(1 + beta)) * t/RTT
*
*/
static uint32_t
tcp_cubic_tcpwin(struct tcpcb *tp, struct tcphdr *th)
{
if (tp->t_ccstate->cub_tcp_win == 0) {
tp->t_ccstate->cub_tcp_win = min(tp->snd_cwnd, tp->snd_wnd);
tp->t_ccstate->cub_tcp_bytes_acked = 0;
} else {
tp->t_ccstate->cub_tcp_bytes_acked +=
BYTES_ACKED(th, tp);
if (tp->t_ccstate->cub_tcp_bytes_acked >=
tp->t_ccstate->cub_tcp_win) {
tp->t_ccstate->cub_tcp_bytes_acked -=
tp->t_ccstate->cub_tcp_win;
tp->t_ccstate->cub_tcp_win += tp->t_maxseg;
}
}
return (tp->t_ccstate->cub_tcp_win);
}
/*
* Handle an in-sequence ack during congestion avoidance phase.
*/
static void
tcp_cubic_congestion_avd(struct tcpcb *tp, struct tcphdr *th)
{
u_int32_t cubic_target_win, tcp_win, rtt;
/* Do not increase congestion window in non-validated phase */
if (tcp_cc_is_cwnd_nonvalidated(tp) != 0)
return;
tp->t_bytes_acked += BYTES_ACKED(th, tp);
rtt = get_base_rtt(tp);
/*
* First compute cubic window. If cubic variables are not
* initialized (after coming out of recovery), this call will
* initialize them.
*/
cubic_target_win = tcp_cubic_update(tp, rtt);
/* Compute TCP window if a multiplicative decrease of 0.2 is used */
tcp_win = tcp_cubic_tcpwin(tp, th);
if (tp->snd_cwnd < tcp_win &&
(tcp_cubic_tcp_friendliness == 1 ||
TCP_CUBIC_ENABLE_TCPMODE(tp))) {
/* this connection is in TCP-friendly region */
if (tp->t_bytes_acked >= tp->snd_cwnd) {
tp->t_bytes_acked -= tp->snd_cwnd;
tp->snd_cwnd = min(tcp_win, TCP_MAXWIN << tp->snd_scale);
}
} else {
if (cubic_target_win > tp->snd_cwnd) {
/*
* The target win is computed for the next RTT.
* To reach this value, cwnd will have to be updated
* one segment at a time. Compute how many bytes
* need to be acknowledged before we can increase
* the cwnd by one segment.
*/
u_int64_t incr_win;
incr_win = tp->snd_cwnd * tp->t_maxseg;
incr_win /= (cubic_target_win - tp->snd_cwnd);
if (incr_win > 0 &&
tp->t_bytes_acked >= incr_win) {
tp->t_bytes_acked -= incr_win;
tp->snd_cwnd =
min((tp->snd_cwnd + tp->t_maxseg),
TCP_MAXWIN << tp->snd_scale);
}
}
}
}
static void
tcp_cubic_ack_rcvd(struct tcpcb *tp, struct tcphdr *th)
{
/* Do not increase the congestion window in non-validated phase */
if (tcp_cc_is_cwnd_nonvalidated(tp) != 0)
return;
if (tp->snd_cwnd >= tp->snd_ssthresh) {
/* Congestion avoidance phase */
tcp_cubic_congestion_avd(tp, th);
} else {
/*
* Use 2*SMSS as limit on increment as suggested
* by RFC 3465 section 2.3
*/
uint32_t acked, abc_lim, incr;
acked = BYTES_ACKED(th, tp);
abc_lim = (tcp_do_rfc3465_lim2 &&
tp->snd_nxt == tp->snd_max) ?
2 * tp->t_maxseg : tp->t_maxseg;
incr = min(acked, abc_lim);
tp->snd_cwnd += incr;
tp->snd_cwnd = min(tp->snd_cwnd,
TCP_MAXWIN << tp->snd_scale);
}
}
static void
tcp_cubic_pre_fr(struct tcpcb *tp)
{
u_int32_t win, avg;
int32_t dev;
tp->t_ccstate->cub_epoch_start = 0;
tp->t_ccstate->cub_tcp_win = 0;
tp->t_ccstate->cub_target_win = 0;
tp->t_ccstate->cub_tcp_bytes_acked = 0;
win = min(tp->snd_cwnd, tp->snd_wnd);
if (tp->t_flagsext & TF_CWND_NONVALIDATED) {
tp->t_lossflightsize = tp->snd_max - tp->snd_una;
win = (max(tp->t_pipeack, tp->t_lossflightsize)) >> 1;
} else {
tp->t_lossflightsize = 0;
}
/*
* Note the congestion window at which packet loss occurred as
* cub_last_max.
*
* If the congestion window is less than the last max window when
* loss occurred, it indicates that capacity available in the
* network has gone down. This can happen if a new flow has started
* and it is capturing some of the bandwidth. To reach convergence
* quickly, backoff a little more. Disable fast convergence to
* disable this behavior.
*/
if (win < tp->t_ccstate->cub_last_max &&
tcp_cubic_fast_convergence == 1)
tp->t_ccstate->cub_last_max = (u_int32_t)(win *
tcp_cubic_fast_convergence_factor);
else
tp->t_ccstate->cub_last_max = win;
if (tp->t_ccstate->cub_last_max == 0) {
/*
* If last_max is zero because snd_wnd is zero or for
* any other reason, initialize it to the amount of data
* in flight
*/
tp->t_ccstate->cub_last_max = tp->snd_max - tp->snd_una;
}
/*
* Compute average and mean absolute deviation of the
* window at which packet loss occurred.
*/
if (tp->t_ccstate->cub_avg_lastmax == 0) {
tp->t_ccstate->cub_avg_lastmax = tp->t_ccstate->cub_last_max;
} else {
/*
* Average is computed by taking 63 parts of
* history and one part of the most recent value
*/
avg = tp->t_ccstate->cub_avg_lastmax;
avg = (avg << 6) - avg;
tp->t_ccstate->cub_avg_lastmax =
(avg + tp->t_ccstate->cub_last_max) >> 6;
}
/* caluclate deviation from average */
dev = tp->t_ccstate->cub_avg_lastmax - tp->t_ccstate->cub_last_max;
/* Take the absolute value */
if (dev < 0)
dev = -dev;
if (tp->t_ccstate->cub_mean_dev == 0) {
tp->t_ccstate->cub_mean_dev = dev;
} else {
dev = dev + ((tp->t_ccstate->cub_mean_dev << 4)
- tp->t_ccstate->cub_mean_dev);
tp->t_ccstate->cub_mean_dev = dev >> 4;
}
/* Backoff congestion window by tcp_cubic_backoff factor */
win = (u_int32_t)(win - (win * tcp_cubic_backoff));
win = (win / tp->t_maxseg);
if (win < 2)
win = 2;
tp->snd_ssthresh = win * tp->t_maxseg;
tcp_cc_resize_sndbuf(tp);
}
static void
tcp_cubic_post_fr(struct tcpcb *tp, struct tcphdr *th)
{
uint32_t flight_size = 0;
if (SEQ_LEQ(th->th_ack, tp->snd_max))
flight_size = tp->snd_max - th->th_ack;
if (SACK_ENABLED(tp) && tp->t_lossflightsize > 0) {
u_int32_t total_rxt_size = 0, ncwnd;
/*
* When SACK is enabled, the number of retransmitted bytes
* can be counted more accurately.
*/
total_rxt_size = tcp_rxtseg_total_size(tp);
ncwnd = max(tp->t_pipeack, tp->t_lossflightsize);
if (total_rxt_size <= ncwnd) {
ncwnd = ncwnd - total_rxt_size;
}
/*
* To avoid sending a large burst at the end of recovery
* set a max limit on ncwnd
*/
ncwnd = min(ncwnd, (tp->t_maxseg << 6));
ncwnd = ncwnd >> 1;
flight_size = max(ncwnd, flight_size);
}
/*
* Complete ack. The current window was inflated for fast recovery.
* It has to be deflated post recovery.
*
* Window inflation should have left us with approx snd_ssthresh
* outstanding data. If the flight size is zero or one segment,
* make congestion window to be at least as big as 2 segments to
* avoid delayed acknowledgements. This is according to RFC 6582.
*/
if (flight_size < tp->snd_ssthresh)
tp->snd_cwnd = max(flight_size, tp->t_maxseg)
+ tp->t_maxseg;
else
tp->snd_cwnd = tp->snd_ssthresh;
tp->t_ccstate->cub_tcp_win = 0;
tp->t_ccstate->cub_target_win = 0;
tp->t_ccstate->cub_tcp_bytes_acked = 0;
}
static void
tcp_cubic_after_timeout(struct tcpcb *tp)
{
VERIFY(tp->t_ccstate != NULL);
/*
* Avoid adjusting congestion window due to SYN retransmissions.
* If more than one byte (SYN) is outstanding then it is still
* needed to adjust the window.
*/
if (tp->t_state < TCPS_ESTABLISHED &&
((int)(tp->snd_max - tp->snd_una) <= 1))
return;
if (!IN_FASTRECOVERY(tp)) {
tcp_cubic_clear_state(tp);
tcp_cubic_pre_fr(tp);
}
/*
* Close the congestion window down to one segment as a retransmit
* timeout might indicate severe congestion.
*/
tp->snd_cwnd = tp->t_maxseg;
}
static int
tcp_cubic_delay_ack(struct tcpcb *tp, struct tcphdr *th)
{
return (tcp_cc_delay_ack(tp, th));
}
/*
* When switching from a different CC it is better for Cubic to start
* fresh. The state required for Cubic calculation might be stale and it
* might not represent the current state of the network. If it starts as
* a new connection it will probe and learn the existing network conditions.
*/
static void
tcp_cubic_switch_cc(struct tcpcb *tp, uint16_t old_cc_index)
{
#pragma unused(old_cc_index)
tcp_cubic_cwnd_init_or_reset(tp);
OSIncrementAtomic((volatile SInt32 *)&tcp_cc_cubic.num_sockets);
}
static inline void tcp_cubic_clear_state(struct tcpcb *tp)
{
tp->t_ccstate->cub_last_max = 0;
tp->t_ccstate->cub_epoch_start = 0;
tp->t_ccstate->cub_origin_point = 0;
tp->t_ccstate->cub_tcp_win = 0;
tp->t_ccstate->cub_tcp_bytes_acked = 0;
tp->t_ccstate->cub_epoch_period = 0;
tp->t_ccstate->cub_target_win = 0;
}
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