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 <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: H.K. Jerry Chu <hkchu@google.com>
Cc: John Heffner <johnwheffner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index e911e6c..6df36ad 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -32,17 +32,6 @@
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 @@
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 @@
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:;
}
-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 @@
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 @@
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);