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