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![Stephen Hemminger](/assets/img/avatar_default.png)
Many of the TCP congestion methods all just use ssthresh as the minimum congestion window on decrease. Rather than duplicating the code, just have that be the default if that handle in the ops structure is not set. Minor behaviour change to TCP compound. It probably wants to use this (ssthresh) as lower bound, rather than ssthresh/2 because the latter causes undershoot on loss. Signed-off-by: Stephen Hemminger <shemminger@osdl.org> Signed-off-by: David S. Miller <davem@davemloft.net>
281 lines
6.7 KiB
C
281 lines
6.7 KiB
C
/*
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* Plugable TCP congestion control support and newReno
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* congestion control.
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* Based on ideas from I/O scheduler suport and Web100.
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*
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* Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
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*/
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#include <linux/config.h>
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#include <linux/module.h>
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#include <linux/mm.h>
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#include <linux/types.h>
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#include <linux/list.h>
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#include <net/tcp.h>
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static DEFINE_SPINLOCK(tcp_cong_list_lock);
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static LIST_HEAD(tcp_cong_list);
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/* Simple linear search, don't expect many entries! */
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static struct tcp_congestion_ops *tcp_ca_find(const char *name)
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{
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struct tcp_congestion_ops *e;
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list_for_each_entry_rcu(e, &tcp_cong_list, list) {
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if (strcmp(e->name, name) == 0)
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return e;
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}
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return NULL;
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}
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/*
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* Attach new congestion control algorthim to the list
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* of available options.
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*/
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int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
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{
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int ret = 0;
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/* all algorithms must implement ssthresh and cong_avoid ops */
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if (!ca->ssthresh || !ca->cong_avoid) {
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printk(KERN_ERR "TCP %s does not implement required ops\n",
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ca->name);
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return -EINVAL;
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}
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spin_lock(&tcp_cong_list_lock);
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if (tcp_ca_find(ca->name)) {
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printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
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ret = -EEXIST;
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} else {
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list_add_rcu(&ca->list, &tcp_cong_list);
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printk(KERN_INFO "TCP %s registered\n", ca->name);
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}
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spin_unlock(&tcp_cong_list_lock);
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return ret;
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}
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EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
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/*
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* Remove congestion control algorithm, called from
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* the module's remove function. Module ref counts are used
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* to ensure that this can't be done till all sockets using
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* that method are closed.
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*/
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void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
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{
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spin_lock(&tcp_cong_list_lock);
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list_del_rcu(&ca->list);
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spin_unlock(&tcp_cong_list_lock);
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}
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EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
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/* Assign choice of congestion control. */
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void tcp_init_congestion_control(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct tcp_congestion_ops *ca;
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if (icsk->icsk_ca_ops != &tcp_init_congestion_ops)
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return;
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rcu_read_lock();
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list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
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if (try_module_get(ca->owner)) {
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icsk->icsk_ca_ops = ca;
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break;
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}
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}
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rcu_read_unlock();
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if (icsk->icsk_ca_ops->init)
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icsk->icsk_ca_ops->init(sk);
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}
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/* Manage refcounts on socket close. */
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void tcp_cleanup_congestion_control(struct sock *sk)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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if (icsk->icsk_ca_ops->release)
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icsk->icsk_ca_ops->release(sk);
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module_put(icsk->icsk_ca_ops->owner);
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}
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/* Used by sysctl to change default congestion control */
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int tcp_set_default_congestion_control(const char *name)
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{
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struct tcp_congestion_ops *ca;
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int ret = -ENOENT;
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spin_lock(&tcp_cong_list_lock);
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ca = tcp_ca_find(name);
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#ifdef CONFIG_KMOD
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if (!ca) {
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spin_unlock(&tcp_cong_list_lock);
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request_module("tcp_%s", name);
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spin_lock(&tcp_cong_list_lock);
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ca = tcp_ca_find(name);
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}
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#endif
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if (ca) {
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list_move(&ca->list, &tcp_cong_list);
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ret = 0;
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}
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spin_unlock(&tcp_cong_list_lock);
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return ret;
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}
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/* Get current default congestion control */
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void tcp_get_default_congestion_control(char *name)
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{
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struct tcp_congestion_ops *ca;
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/* We will always have reno... */
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BUG_ON(list_empty(&tcp_cong_list));
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rcu_read_lock();
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ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
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strncpy(name, ca->name, TCP_CA_NAME_MAX);
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rcu_read_unlock();
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}
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/* Change congestion control for socket */
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int tcp_set_congestion_control(struct sock *sk, const char *name)
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{
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struct inet_connection_sock *icsk = inet_csk(sk);
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struct tcp_congestion_ops *ca;
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int err = 0;
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rcu_read_lock();
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ca = tcp_ca_find(name);
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if (ca == icsk->icsk_ca_ops)
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goto out;
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if (!ca)
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err = -ENOENT;
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else if (!try_module_get(ca->owner))
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err = -EBUSY;
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else {
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tcp_cleanup_congestion_control(sk);
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icsk->icsk_ca_ops = ca;
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if (icsk->icsk_ca_ops->init)
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icsk->icsk_ca_ops->init(sk);
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}
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out:
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rcu_read_unlock();
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return err;
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}
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/*
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* Linear increase during slow start
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*/
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void tcp_slow_start(struct tcp_sock *tp)
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{
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if (sysctl_tcp_abc) {
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/* RFC3465: Slow Start
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* TCP sender SHOULD increase cwnd by the number of
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* previously unacknowledged bytes ACKed by each incoming
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* acknowledgment, provided the increase is not more than L
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*/
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if (tp->bytes_acked < tp->mss_cache)
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return;
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/* We MAY increase by 2 if discovered delayed ack */
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if (sysctl_tcp_abc > 1 && tp->bytes_acked > 2*tp->mss_cache) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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}
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}
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tp->bytes_acked = 0;
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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}
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EXPORT_SYMBOL_GPL(tcp_slow_start);
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/*
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* TCP Reno congestion control
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* This is special case used for fallback as well.
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*/
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/* This is Jacobson's slow start and congestion avoidance.
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* SIGCOMM '88, p. 328.
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*/
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void tcp_reno_cong_avoid(struct sock *sk, u32 ack, u32 rtt, u32 in_flight,
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int flag)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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if (!tcp_is_cwnd_limited(sk, in_flight))
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return;
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/* In "safe" area, increase. */
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if (tp->snd_cwnd <= tp->snd_ssthresh)
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tcp_slow_start(tp);
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/* In dangerous area, increase slowly. */
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else if (sysctl_tcp_abc) {
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/* RFC3465: Appropriate Byte Count
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* increase once for each full cwnd acked
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*/
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if (tp->bytes_acked >= tp->snd_cwnd*tp->mss_cache) {
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tp->bytes_acked -= tp->snd_cwnd*tp->mss_cache;
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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}
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} else {
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/* In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd */
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if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
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if (tp->snd_cwnd < tp->snd_cwnd_clamp)
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tp->snd_cwnd++;
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tp->snd_cwnd_cnt = 0;
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} else
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tp->snd_cwnd_cnt++;
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}
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}
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EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
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/* Slow start threshold is half the congestion window (min 2) */
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u32 tcp_reno_ssthresh(struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return max(tp->snd_cwnd >> 1U, 2U);
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}
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EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
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/* Lower bound on congestion window with halving. */
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u32 tcp_reno_min_cwnd(const struct sock *sk)
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{
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const struct tcp_sock *tp = tcp_sk(sk);
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return tp->snd_ssthresh/2;
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}
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EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
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struct tcp_congestion_ops tcp_reno = {
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.name = "reno",
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.owner = THIS_MODULE,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.min_cwnd = tcp_reno_min_cwnd,
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};
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/* Initial congestion control used (until SYN)
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* really reno under another name so we can tell difference
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* during tcp_set_default_congestion_control
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*/
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struct tcp_congestion_ops tcp_init_congestion_ops = {
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.name = "",
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.owner = THIS_MODULE,
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.ssthresh = tcp_reno_ssthresh,
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.cong_avoid = tcp_reno_cong_avoid,
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.min_cwnd = tcp_reno_min_cwnd,
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};
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EXPORT_SYMBOL_GPL(tcp_init_congestion_ops);
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