From 6f458dfb409272082c9bfa412f77ff2fc21c626f Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 20 Jul 2012 05:45:50 +0000 Subject: tcp: improve latencies of timer triggered events Modern TCP stack highly depends on tcp_write_timer() having a small latency, but current implementation doesn't exactly meet the expectations. When a timer fires but finds the socket is owned by the user, it rearms itself for an additional delay hoping next run will be more successful. tcp_write_timer() for example uses a 50ms delay for next try, and it defeats many attempts to get predictable TCP behavior in term of latencies. Use the recently introduced tcp_release_cb(), so that the user owning the socket will call various handlers right before socket release. This will permit us to post a followup patch to address the tcp_tso_should_defer() syndrome (some deferred packets have to wait RTO timer to be transmitted, while cwnd should allow us to send them sooner) Signed-off-by: Eric Dumazet Cc: Tom Herbert Cc: Yuchung Cheng Cc: Neal Cardwell Cc: Nandita Dukkipati Cc: H.K. Jerry Chu Cc: John Heffner Signed-off-by: David S. Miller --- net/ipv4/tcp_timer.c | 70 +++++++++++++++++++++++++++------------------------- 1 file changed, 37 insertions(+), 33 deletions(-) (limited to 'net/ipv4/tcp_timer.c') diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index e911e6c523ec..6df36ad55a38 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -32,17 +32,6 @@ int sysctl_tcp_retries2 __read_mostly = TCP_RETR2; int sysctl_tcp_orphan_retries __read_mostly; int sysctl_tcp_thin_linear_timeouts __read_mostly; -static void tcp_write_timer(unsigned long); -static void tcp_delack_timer(unsigned long); -static void tcp_keepalive_timer (unsigned long data); - -void tcp_init_xmit_timers(struct sock *sk) -{ - inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, - &tcp_keepalive_timer); -} -EXPORT_SYMBOL(tcp_init_xmit_timers); - static void tcp_write_err(struct sock *sk) { sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT; @@ -205,21 +194,11 @@ static int tcp_write_timeout(struct sock *sk) return 0; } -static void tcp_delack_timer(unsigned long data) +void tcp_delack_timer_handler(struct sock *sk) { - struct sock *sk = (struct sock *)data; struct tcp_sock *tp = tcp_sk(sk); struct inet_connection_sock *icsk = inet_csk(sk); - bh_lock_sock(sk); - if (sock_owned_by_user(sk)) { - /* Try again later. */ - icsk->icsk_ack.blocked = 1; - NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); - sk_reset_timer(sk, &icsk->icsk_delack_timer, jiffies + TCP_DELACK_MIN); - goto out_unlock; - } - sk_mem_reclaim_partial(sk); if (sk->sk_state == TCP_CLOSE || !(icsk->icsk_ack.pending & ICSK_ACK_TIMER)) @@ -260,7 +239,21 @@ static void tcp_delack_timer(unsigned long data) out: if (sk_under_memory_pressure(sk)) sk_mem_reclaim(sk); -out_unlock: +} + +static void tcp_delack_timer(unsigned long data) +{ + struct sock *sk = (struct sock *)data; + + bh_lock_sock(sk); + if (!sock_owned_by_user(sk)) { + tcp_delack_timer_handler(sk); + } else { + inet_csk(sk)->icsk_ack.blocked = 1; + NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED); + /* deleguate our work to tcp_release_cb() */ + set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); + } bh_unlock_sock(sk); sock_put(sk); } @@ -450,19 +443,11 @@ out_reset_timer: out:; } -static void tcp_write_timer(unsigned long data) +void tcp_write_timer_handler(struct sock *sk) { - struct sock *sk = (struct sock *)data; struct inet_connection_sock *icsk = inet_csk(sk); int event; - bh_lock_sock(sk); - if (sock_owned_by_user(sk)) { - /* Try again later */ - sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + (HZ / 20)); - goto out_unlock; - } - if (sk->sk_state == TCP_CLOSE || !icsk->icsk_pending) goto out; @@ -485,7 +470,19 @@ static void tcp_write_timer(unsigned long data) out: sk_mem_reclaim(sk); -out_unlock: +} + +static void tcp_write_timer(unsigned long data) +{ + struct sock *sk = (struct sock *)data; + + bh_lock_sock(sk); + if (!sock_owned_by_user(sk)) { + tcp_write_timer_handler(sk); + } else { + /* deleguate our work to tcp_release_cb() */ + set_bit(TCP_WRITE_TIMER_DEFERRED, &tcp_sk(sk)->tsq_flags); + } bh_unlock_sock(sk); sock_put(sk); } @@ -602,3 +599,10 @@ out: bh_unlock_sock(sk); sock_put(sk); } + +void tcp_init_xmit_timers(struct sock *sk) +{ + inet_csk_init_xmit_timers(sk, &tcp_write_timer, &tcp_delack_timer, + &tcp_keepalive_timer); +} +EXPORT_SYMBOL(tcp_init_xmit_timers); -- cgit v1.2.3-59-g8ed1b