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Miller" , Jakub Kicinski , Paolo Abeni Cc: Neal Cardwell , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet X-Patchwork-Delegate: kuba@kernel.org delack timer is not stopped from inet_csk_clear_xmit_timer() because we do not define INET_CSK_CLEAR_TIMERS. This is a conscious choice : inet_csk_clear_xmit_timer() is often called from another cpu. Calling del_timer() would cause false sharing and lock contention. This means that very often, tcp_delack_timer() is called at the timer expiration, while there is no ACK to transmit. This can be detected very early, avoiding the socket spinlock. Notes: - test about tp->compressed_ack is racy, but in the unlikely case there is a race, the dedicated compressed_ack_timer hrtimer would close it. - Even if the fast path is not taken, reading icsk->icsk_ack.pending and tp->compressed_ack before acquiring the socket spinlock reduces acquisition time and chances of contention. Signed-off-by: Eric Dumazet --- include/net/inet_connection_sock.h | 5 +++-- net/ipv4/inet_connection_sock.c | 4 ++-- net/ipv4/tcp_output.c | 3 ++- net/ipv4/tcp_timer.c | 9 +++++++++ net/mptcp/protocol.c | 3 ++- 5 files changed, 18 insertions(+), 6 deletions(-) diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h index 914d1977270449241f6fc6da2055f3af02a75f99..3c82fad904d4c6c51069e2e703673d667bb36d06 100644 --- a/include/net/inet_connection_sock.h +++ b/include/net/inet_connection_sock.h @@ -202,7 +202,7 @@ static inline void inet_csk_clear_xmit_timer(struct sock *sk, const int what) sk_stop_timer(sk, &icsk->icsk_retransmit_timer); #endif } else if (what == ICSK_TIME_DACK) { - icsk->icsk_ack.pending = 0; + smp_store_release(&icsk->icsk_ack.pending, 0); icsk->icsk_ack.retry = 0; #ifdef INET_CSK_CLEAR_TIMERS sk_stop_timer(sk, &icsk->icsk_delack_timer); @@ -233,7 +233,8 @@ static inline void inet_csk_reset_xmit_timer(struct sock *sk, const int what, icsk->icsk_timeout = jiffies + when; sk_reset_timer(sk, &icsk->icsk_retransmit_timer, icsk->icsk_timeout); } else if (what == ICSK_TIME_DACK) { - icsk->icsk_ack.pending |= ICSK_ACK_TIMER; + smp_store_release(&icsk->icsk_ack.pending, + icsk->icsk_ack.pending | ICSK_ACK_TIMER); icsk->icsk_ack.timeout = jiffies + when; sk_reset_timer(sk, &icsk->icsk_delack_timer, icsk->icsk_ack.timeout); } else { diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index 8c53385cc808c61097898514fd91a322e3a08d31..12e975ed4910d8c7cca79b1812f365589a5d469a 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -776,7 +776,7 @@ void inet_csk_clear_xmit_timers(struct sock *sk) struct inet_connection_sock *icsk = inet_csk(sk); smp_store_release(&icsk->icsk_pending, 0); - icsk->icsk_ack.pending = 0; + smp_store_release(&icsk->icsk_ack.pending, 0); sk_stop_timer(sk, &icsk->icsk_retransmit_timer); sk_stop_timer(sk, &icsk->icsk_delack_timer); @@ -792,7 +792,7 @@ void inet_csk_clear_xmit_timers_sync(struct sock *sk) sock_not_owned_by_me(sk); smp_store_release(&icsk->icsk_pending, 0); - icsk->icsk_ack.pending = 0; + smp_store_release(&icsk->icsk_ack.pending, 0); sk_stop_timer_sync(sk, &icsk->icsk_retransmit_timer); sk_stop_timer_sync(sk, &icsk->icsk_delack_timer); diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 4d04073016035dcf62ba5e0ad23aac86e54e65c7..08772395690d13a0c3309a273543a51aa0dd3fdc 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -4224,7 +4224,8 @@ void tcp_send_delayed_ack(struct sock *sk) if (!time_before(timeout, icsk->icsk_ack.timeout)) timeout = icsk->icsk_ack.timeout; } - icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; + smp_store_release(&icsk->icsk_ack.pending, + icsk->icsk_ack.pending | ICSK_ACK_SCHED | ICSK_ACK_TIMER); icsk->icsk_ack.timeout = timeout; sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout); } diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index b7266b9101ce5933776bd38d086287667e3a7f18..c3a7442332d4926a6089812f789e89ee23081306 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -361,6 +361,14 @@ static void tcp_delack_timer(struct timer_list *t) from_timer(icsk, t, icsk_delack_timer); struct sock *sk = &icsk->icsk_inet.sk; + /* Avoid taking socket spinlock if there is no ACK to send. + * The compressed_ack check is racy, but a separate hrtimer + * will take care of it eventually. + */ + if (!(smp_load_acquire(&icsk->icsk_ack.pending) & ICSK_ACK_TIMER) && + !READ_ONCE(tcp_sk(sk)->compressed_ack)) + goto out; + bh_lock_sock(sk); if (!sock_owned_by_user(sk)) { tcp_delack_timer_handler(sk); @@ -371,6 +379,7 @@ static void tcp_delack_timer(struct timer_list *t) sock_hold(sk); } bh_unlock_sock(sk); +out: sock_put(sk); } diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index c2317919fc148a67a81ded795359bd613c9b0dff..e85862352084907582ec884dcb96832356419fa5 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -3504,7 +3504,8 @@ static void schedule_3rdack_retransmission(struct sock *ssk) timeout += jiffies; WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER); - icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER; + smp_store_release(&icsk->icsk_ack.pending, + icsk->icsk_ack.pending | ICSK_ACK_SCHED | ICSK_ACK_TIMER); icsk->icsk_ack.timeout = timeout; sk_reset_timer(ssk, &icsk->icsk_delack_timer, timeout); }