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authorFrancis Yan <francisyyan@gmail.com>2016-11-27 23:07:16 -0800
committerDavid S. Miller <davem@davemloft.net>2016-11-30 10:04:24 -0500
commitb0f71bd3e190df827d25d7f19bf09037567f14b7 (patch)
tree4f65ddefad045bc8a14d438a7ea6252212e51d3c
parent5615f88614a47d2b802e1d14d31b623696109276 (diff)
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>
-rw-r--r--net/ipv4/tcp.c10
-rw-r--r--net/ipv4/tcp_input.c5
-rw-r--r--net/ipv4/tcp_output.c12
3 files changed, 24 insertions, 3 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 913f9bb..259ffb5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -996,8 +996,11 @@ do_error:
goto out;
out_err:
/* make sure we wake any epoll edge trigger waiter */
- if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
+ if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&
+ err == -EAGAIN)) {
sk->sk_write_space(sk);
+ tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
+ }
return sk_stream_error(sk, flags, err);
}
@@ -1331,8 +1334,11 @@ do_error:
out_err:
err = sk_stream_error(sk, flags, err);
/* make sure we wake any epoll edge trigger waiter */
- if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 && err == -EAGAIN))
+ if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&
+ err == -EAGAIN)) {
sk->sk_write_space(sk);
+ tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
+ }
release_sock(sk);
return err;
}
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);
+ }
}
}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b74444c..d3545d0 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1514,6 +1514,18 @@ static void tcp_cwnd_validate(struct sock *sk, bool is_cwnd_limited)
if (sysctl_tcp_slow_start_after_idle &&
(s32)(tcp_time_stamp - tp->snd_cwnd_stamp) >= inet_csk(sk)->icsk_rto)
tcp_cwnd_application_limited(sk);
+
+ /* The following conditions together indicate the starvation
+ * is caused by insufficient sender buffer:
+ * 1) just sent some data (see tcp_write_xmit)
+ * 2) not cwnd limited (this else condition)
+ * 3) no more data to send (null tcp_send_head )
+ * 4) application is hitting buffer limit (SOCK_NOSPACE)
+ */
+ if (!tcp_send_head(sk) && sk->sk_socket &&
+ test_bit(SOCK_NOSPACE, &sk->sk_socket->flags) &&
+ (1 << sk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT))
+ tcp_chrono_start(sk, TCP_CHRONO_SNDBUF_LIMITED);
}
}