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Message-ID: <CACSApvYnw_9Bj8SowATJYJ_R2-W5od7f8VAFjEh0cM2BCrBB5A@mail.gmail.com>
Date: Wed, 30 Sep 2020 09:45:07 -0400
From: Soheil Hassas Yeganeh <soheil@...gle.com>
To: Eric Dumazet <eric.dumazet@...il.com>
Cc: "David S . Miller" <davem@...emloft.net>,
netdev <netdev@...r.kernel.org>,
Neal Cardwell <ncardwell@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>,
Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next 1/2] inet: remove icsk_ack.blocked
On Wed, Sep 30, 2020 at 8:55 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> From: Eric Dumazet <edumazet@...gle.com>
>
> TCP has been using it to work around the possibility of tcp_delack_timer()
> finding the socket owned by user.
>
> After commit 6f458dfb4092 ("tcp: improve latencies of timer triggered events")
> we added TCP_DELACK_TIMER_DEFERRED atomic bit for more immediate recovery,
> so we can get rid of icsk_ack.blocked
>
> This frees space that following patch will reuse.
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> ---
> include/net/inet_connection_sock.h | 4 ++--
> net/dccp/timer.c | 1 -
> net/ipv4/inet_connection_sock.c | 2 +-
> net/ipv4/tcp.c | 6 ++----
> net/ipv4/tcp_output.c | 7 ++-----
> net/ipv4/tcp_timer.c | 1 -
> 6 files changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
> index dc763ca9413cc9c6279a59f9d1776cf2dbb1e853..79875f976190750819948425e63dd0309c699050 100644
> --- a/include/net/inet_connection_sock.h
> +++ b/include/net/inet_connection_sock.h
> @@ -110,7 +110,7 @@ struct inet_connection_sock {
> __u8 pending; /* ACK is pending */
> __u8 quick; /* Scheduled number of quick acks */
> __u8 pingpong; /* The session is interactive */
> - __u8 blocked; /* Delayed ACK was blocked by socket lock */
> + /* one byte hole. */
> __u32 ato; /* Predicted tick of soft clock */
> unsigned long timeout; /* Currently scheduled timeout */
> __u32 lrcvtime; /* timestamp of last received data packet */
> @@ -198,7 +198,7 @@ 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.blocked = icsk->icsk_ack.pending = 0;
> + icsk->icsk_ack.pending = 0;
> #ifdef INET_CSK_CLEAR_TIMERS
> sk_stop_timer(sk, &icsk->icsk_delack_timer);
> #endif
> diff --git a/net/dccp/timer.c b/net/dccp/timer.c
> index 927c796d76825439a35c4deb3fb2e45e4313f9b3..a934d293237366aeca87bd3c32241880639291c5 100644
> --- a/net/dccp/timer.c
> +++ b/net/dccp/timer.c
> @@ -176,7 +176,6 @@ static void dccp_delack_timer(struct timer_list *t)
> bh_lock_sock(sk);
> if (sock_owned_by_user(sk)) {
> /* Try again later. */
> - icsk->icsk_ack.blocked = 1;
> __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
> sk_reset_timer(sk, &icsk->icsk_delack_timer,
> jiffies + TCP_DELACK_MIN);
> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
> index b457dd2d6c75b2f63bc7849474ac909adb14d603..4148f5f78f313cde1e0596b9eb3696df16e3f990 100644
> --- a/net/ipv4/inet_connection_sock.c
> +++ b/net/ipv4/inet_connection_sock.c
> @@ -564,7 +564,7 @@ void inet_csk_clear_xmit_timers(struct sock *sk)
> {
> struct inet_connection_sock *icsk = inet_csk(sk);
>
> - icsk->icsk_pending = icsk->icsk_ack.pending = icsk->icsk_ack.blocked = 0;
> + icsk->icsk_pending = icsk->icsk_ack.pending = 0;
>
> sk_stop_timer(sk, &icsk->icsk_retransmit_timer);
> sk_stop_timer(sk, &icsk->icsk_delack_timer);
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 2a8bfa89a5159837e3687e4e0f8cddba7fe54899..ed2805564424a90f003eed867bbed7f5ac4ae833 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -1538,10 +1538,8 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied)
>
> if (inet_csk_ack_scheduled(sk)) {
> const struct inet_connection_sock *icsk = inet_csk(sk);
> - /* Delayed ACKs frequently hit locked sockets during bulk
> - * receive. */
> - if (icsk->icsk_ack.blocked ||
> - /* Once-per-two-segments ACK was not sent by tcp_input.c */
> +
> + if (/* Once-per-two-segments ACK was not sent by tcp_input.c */
> tp->rcv_nxt - tp->rcv_wup > icsk->icsk_ack.rcv_mss ||
> /*
> * If this read emptied read buffer, we send ACK, if
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 386978dcd318d84af486d0d1a5bb1786f4a493cf..6bd4e383030ea20441332a30e98fbda8cd90f84a 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3911,11 +3911,8 @@ void tcp_send_delayed_ack(struct sock *sk)
>
> /* Use new timeout only if there wasn't a older one earlier. */
> if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
> - /* If delack timer was blocked or is about to expire,
> - * send ACK now.
> - */
> - if (icsk->icsk_ack.blocked ||
> - time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
> + /* If delack timer is about to expire, send ACK now. */
> + if (time_before_eq(icsk->icsk_ack.timeout, jiffies + (ato >> 2))) {
> tcp_send_ack(sk);
> return;
> }
> diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> index 0c08c420fbc21a98dedf72148ea2a6f85bf3ff7a..6c62b9ea1320d9bbd26ed86b9f41de02fee6c491 100644
> --- a/net/ipv4/tcp_timer.c
> +++ b/net/ipv4/tcp_timer.c
> @@ -331,7 +331,6 @@ static void tcp_delack_timer(struct timer_list *t)
> if (!sock_owned_by_user(sk)) {
> tcp_delack_timer_handler(sk);
> } else {
> - icsk->icsk_ack.blocked = 1;
> __NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
> /* deleguate our work to tcp_release_cb() */
> if (!test_and_set_bit(TCP_DELACK_TIMER_DEFERRED, &sk->sk_tsq_flags))
> --
> 2.28.0.806.g8561365e88-goog
>
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