tcp: instrument how long TCP is limited by insufficient send buffer
This patch measures the amount of time when TCP runs out of new data
to send to the network due to insufficient send buffer, while TCP
is still busy delivering (i.e. write queue is not empty). The goal
is to indicate either the send buffer autotuning or user SO_SNDBUF
setting has resulted network under-utilization.
The measurement starts conservatively by checking various conditions
to minimize false claims (i.e. under-estimation is more likely).
The measurement stops when the SOCK_NOSPACE flag is cleared. But it
does not account the time elapsed till the next application write.
Also the measurement only starts if the sender is still busy sending
data, s.t. the limit accounted is part of the total busy time.
Signed-off-by: Francis Yan <francisyyan@gmail.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a5d1727..56fe736 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5059,8 +5059,11 @@ static void tcp_check_space(struct sock *sk)
/* pairs with tcp_poll() */
smp_mb__after_atomic();
if (sk->sk_socket &&
- test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
+ test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
tcp_new_space(sk);
+ if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
+ tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
+ }
}
}
