/*
* Copyright (c) 2013-2021 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
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* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
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*/
#include "tcp_includes.h"
#include <sys/param.h>
#include <sys/kernel.h>
#include <sys/syslog.h>
#include <sys/kern_control.h>
#include <sys/domain.h>
#include <netinet/in.h>
#include <mach/sdt.h>
#include <libkern/OSAtomic.h>
#include <libkern/OSTypes.h>
extern struct tcp_cc_algo tcp_cc_newreno;
extern struct tcp_cc_algo tcp_cc_ledbat;
extern struct tcp_cc_algo tcp_cc_cubic;
#define SET_SNDSB_IDEAL_SIZE(sndsb, size) \
sndsb->sb_idealsize = min(max(tcp_sendspace, tp->snd_ssthresh), \
tcp_autosndbuf_max);
/* Array containing pointers to currently implemented TCP CC algorithms */
struct tcp_cc_algo* tcp_cc_algo_list[TCP_CC_ALGO_COUNT];
static struct tcp_cc_algo tcp_cc_algo_none;
/*
* Initialize TCP congestion control algorithms.
*/
void
tcp_cc_init(void)
{
bzero(&tcp_cc_algo_list, sizeof(tcp_cc_algo_list));
bzero(&tcp_cc_algo_none, sizeof(tcp_cc_algo_none));
tcp_cc_algo_list[TCP_CC_ALGO_NONE] = &tcp_cc_algo_none;
tcp_cc_algo_list[TCP_CC_ALGO_NEWRENO_INDEX] = &tcp_cc_newreno;
tcp_cc_algo_list[TCP_CC_ALGO_BACKGROUND_INDEX] = &tcp_cc_ledbat;
tcp_cc_algo_list[TCP_CC_ALGO_CUBIC_INDEX] = &tcp_cc_cubic;
tcp_ccdbg_control_register();
}
void
tcp_cc_resize_sndbuf(struct tcpcb *tp)
{
struct sockbuf *sb;
/*
* If the send socket buffer size is bigger than ssthresh,
* it is time to trim it because we do not want to hold
* too many mbufs in the socket buffer
*/
sb = &tp->t_inpcb->inp_socket->so_snd;
if (sb->sb_hiwat > tp->snd_ssthresh &&
(sb->sb_flags & SB_AUTOSIZE)) {
if (sb->sb_idealsize > tp->snd_ssthresh) {
SET_SNDSB_IDEAL_SIZE(sb, tp->snd_ssthresh);
}
sb->sb_flags |= SB_TRIM;
}
}
void
tcp_bad_rexmt_fix_sndbuf(struct tcpcb *tp)
{
struct sockbuf *sb;
sb = &tp->t_inpcb->inp_socket->so_snd;
if ((sb->sb_flags & (SB_TRIM | SB_AUTOSIZE)) == (SB_TRIM | SB_AUTOSIZE)) {
/*
* If there was a retransmission that was not necessary
* then the size of socket buffer can be restored to
* what it was before
*/
SET_SNDSB_IDEAL_SIZE(sb, tp->snd_ssthresh);
if (sb->sb_hiwat <= sb->sb_idealsize) {
sbreserve(sb, sb->sb_idealsize);
sb->sb_flags &= ~SB_TRIM;
}
}
}
/*
* Calculate initial cwnd according to RFC3390.
*/
void
tcp_cc_cwnd_init_or_reset(struct tcpcb *tp)
{
if (tp->t_flags & TF_LOCAL) {
tp->snd_cwnd = tp->t_maxseg * ss_fltsz_local;
} else {
if (tcp_cubic_minor_fixes) {
tp->snd_cwnd = tcp_initial_cwnd(tp);
} else {
/* initial congestion window according to RFC 3390 */
tp->snd_cwnd = min(4 * tp->t_maxseg,
max(2 * tp->t_maxseg, TCP_CC_CWND_INIT_BYTES));
}
}
}
/*
* Indicate whether this ack should be delayed.
* Here is the explanation for different settings of tcp_delack_enabled:
* - when set to 1, the behavior is same as when set to 2. We kept this
* for binary compatibility.
* - when set to 2, will "ack every other packet"
* - if our last ack wasn't a 0-sized window.
* - if the peer hasn't sent us a TH_PUSH data packet (radar 3649245).
* If TH_PUSH is set, take this as a clue that we need to ACK
* with no delay. This helps higher level protocols who
* won't send us more data even if the window is open
* because their last "segment" hasn't been ACKed
* - when set to 3, will do "streaming detection"
* - if we receive more than "maxseg_unacked" full packets
* in the last 100ms
* - if the connection is not in slow-start or idle or
* loss/recovery states
* - if those criteria aren't met, it will ack every other packet.
*/
int
tcp_cc_delay_ack(struct tcpcb *tp, struct tcphdr *th)
{
switch (tcp_delack_enabled) {
case 1:
case 2:
if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
(th->th_flags & TH_PUSH) == 0 &&
(tp->t_unacksegs == 1)) {
return 1;
}
break;
case 3:
if (tcp_ack_strategy == TCP_ACK_STRATEGY_LEGACY) {
if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
(th->th_flags & TH_PUSH) == 0 &&
((tp->t_unacksegs == 1) ||
((tp->t_flags & TF_STRETCHACK) &&
tp->t_unacksegs < maxseg_unacked))) {
return 1;
}
} else {
uint32_t recwin;
/* Get the receive-window we would announce */
recwin = tcp_sbspace(tp);
if (recwin > (uint32_t)(TCP_MAXWIN << tp->rcv_scale)) {
recwin = (uint32_t)(TCP_MAXWIN << tp->rcv_scale);
}
/* Delay ACK, if:
*
* 1. We are not sending a zero-window
* 2. We are not forcing fast ACKs
* 3. We have more than the low-water mark in receive-buffer
* 4. The receive-window is not increasing
* 5. We have less than or equal of an MSS unacked or
* Window actually has been growing larger than the initial value by half of it.
* (this makes sure that during ramp-up we ACK every second MSS
* until we pass the tcp_recvspace * 1.5-threshold)
* 6. We haven't waited for half a BDP
* 7. The amount of unacked data is less than the maximum ACK-burst (256 MSS)
* We try to avoid having the sender end up hitting huge ACK-ranges.
*
* (a note on 6: The receive-window is
* roughly 2 BDP. Thus, recwin / 4 means half a BDP and
* thus we enforce an ACK roughly twice per RTT - even
* if the app does not read)
*/
if ((tp->t_flags & TF_RXWIN0SENT) == 0 &&
tp->t_forced_acks == 0 &&
tp->t_inpcb->inp_socket->so_rcv.sb_cc > tp->t_inpcb->inp_socket->so_rcv.sb_lowat &&
recwin <= tp->t_last_recwin &&
(tp->rcv_nxt - tp->last_ack_sent <= tp->t_maxseg ||
recwin > (uint32_t)(tcp_recvspace + (tcp_recvspace >> 1))) &&
(tp->rcv_nxt - tp->last_ack_sent) < (recwin >> 2) &&
(tp->rcv_nxt - tp->last_ack_sent) < 256 * tp->t_maxseg) {
tp->t_stat.acks_delayed++;
return 1;
}
}
break;
}
return 0;
}
void
tcp_cc_allocate_state(struct tcpcb *tp)
{
if ((tp->tcp_cc_index == TCP_CC_ALGO_CUBIC_INDEX ||
tp->tcp_cc_index == TCP_CC_ALGO_BACKGROUND_INDEX) &&
tp->t_ccstate == NULL) {
tp->t_ccstate = &tp->_t_ccstate;
bzero(tp->t_ccstate, sizeof(*tp->t_ccstate));
}
}
/*
* If stretch ack was disabled automatically on long standing connections,
* re-evaluate the situation after 15 minutes to enable it.
*/
#define TCP_STRETCHACK_DISABLE_WIN (15 * 60 * TCP_RETRANSHZ)
void
tcp_cc_after_idle_stretchack(struct tcpcb *tp)
{
struct tcp_globals *globals;
int32_t tdiff;
if (!(tp->t_flagsext & TF_DISABLE_STRETCHACK)) {
return;
}
globals = tcp_get_globals(tp);
tdiff = timer_diff(tcp_globals_now(globals), 0, tp->rcv_nostrack_ts, 0);
if (tdiff < 0) {
tdiff = -tdiff;
}
if (tdiff > TCP_STRETCHACK_DISABLE_WIN) {
tp->t_flagsext &= ~TF_DISABLE_STRETCHACK;
tp->t_stretchack_delayed = 0;
tcp_reset_stretch_ack(tp);
}
}
/*
* Detect if the congestion window is non-validated according to
* draft-ietf-tcpm-newcwv-07
*/
inline uint32_t
tcp_cc_is_cwnd_nonvalidated(struct tcpcb *tp)
{
struct socket *so = tp->t_inpcb->inp_socket;
if (tp->t_pipeack == 0) {
tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
return 0;
}
/*
* The congestion window is validated if the number of bytes acked
* is more than half of the current window or if there is more
* data to send in the send socket buffer
*/
if (tp->t_pipeack >= (tp->snd_cwnd >> 1) ||
(so != NULL && so->so_snd.sb_cc > tp->snd_cwnd)) {
tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
} else {
tp->t_flagsext |= TF_CWND_NONVALIDATED;
}
return tp->t_flagsext & TF_CWND_NONVALIDATED;
}
/*
* Adjust congestion window in response to congestion in non-validated
* phase.
*/
inline void
tcp_cc_adjust_nonvalidated_cwnd(struct tcpcb *tp)
{
tp->t_pipeack = tcp_get_max_pipeack(tp);
tcp_clear_pipeack_state(tp);
tp->snd_cwnd = (max(tp->t_pipeack, tp->t_lossflightsize) >> 1);
if (tcp_cubic_minor_fixes) {
tp->snd_cwnd = max(tp->snd_cwnd, tp->t_maxseg);
} else {
tp->snd_cwnd = max(tp->snd_cwnd, TCP_CC_CWND_INIT_BYTES);
}
tp->snd_cwnd += tp->t_maxseg * tcprexmtthresh;
tp->t_flagsext &= ~TF_CWND_NONVALIDATED;
}
/*
* Return maximum of all the pipeack samples. Since the number of samples
* TCP_PIPEACK_SAMPLE_COUNT is 3 at this time, it will be simpler to do
* a comparision. We should change ths if the number of samples increases.
*/
inline uint32_t
tcp_get_max_pipeack(struct tcpcb *tp)
{
uint32_t max_pipeack = 0;
max_pipeack = (tp->t_pipeack_sample[0] > tp->t_pipeack_sample[1]) ?
tp->t_pipeack_sample[0] : tp->t_pipeack_sample[1];
max_pipeack = (tp->t_pipeack_sample[2] > max_pipeack) ?
tp->t_pipeack_sample[2] : max_pipeack;
return max_pipeack;
}
inline void
tcp_clear_pipeack_state(struct tcpcb *tp)
{
bzero(tp->t_pipeack_sample, sizeof(tp->t_pipeack_sample));
tp->t_pipeack_ind = 0;
tp->t_lossflightsize = 0;
}