| Message ID | 20241002173042.917928-3-edumazet@google.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3b784293016252118ed3b42c5479f20f89a0f384 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | tcp: add fast path in timer handlers | expand |
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 56c597e763ac7a8cebeba324f84e57b1eeeae977..b7266b9101ce5933776bd38d086287667e3a7f18 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -717,6 +717,10 @@ static void tcp_write_timer(struct timer_list *t) from_timer(icsk, t, icsk_retransmit_timer); struct sock *sk = &icsk->icsk_inet.sk; + /* Avoid locking the socket when there is no pending event. */ + if (!smp_load_acquire(&icsk->icsk_pending)) + goto out; + bh_lock_sock(sk); if (!sock_owned_by_user(sk)) { tcp_write_timer_handler(sk); @@ -726,6 +730,7 @@ static void tcp_write_timer(struct timer_list *t) sock_hold(sk); } bh_unlock_sock(sk); +out: sock_put(sk); }
retransmit timer is not stopped from inet_csk_clear_xmit_timer() because we do not define INET_CSK_CLEAR_TIMERS. This is a conscious choice : for active TCP flows, it is better to only call mod_timer(), because there is more chances of keeping the timer unchanged. Also inet_csk_clear_xmit_timer() is often called from another cpu, and calling del_timer() would cause false sharing and lock contention. This means that very often, tcp_write_timer() is called at the timer expiration, while there is nothing to retransmit. This can be detected very early, avoiding the socket spinlock. Signed-off-by: Eric Dumazet <edumazet@google.com> --- net/ipv4/tcp_timer.c | 5 +++++ 1 file changed, 5 insertions(+)