tcp: instrument how long TCP is limited by receive window

This patch measures the total time when the TCP stops sending because
the receiver's advertised window is not large enough. Note that
once the limit is lifted we are likely in the busy status if we
have data pending.

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_output.c b/net/ipv4/tcp_output.c
index e8ea584106e0bf3b6d8da47d382927dd00ca2b08..b74444cee24d361316e180bf68e6049d3ce6492e 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2144,7 +2144,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
        unsigned int tso_segs, sent_pkts;
        int cwnd_quota;
        int result;
-       bool is_cwnd_limited = false;
+       bool is_cwnd_limited = false, is_rwnd_limited = false;
        u32 max_segs;
 
        sent_pkts = 0;
@@ -2181,8 +2181,10 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
                                break;
                }
 
-               if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now)))
+               if (unlikely(!tcp_snd_wnd_test(tp, skb, mss_now))) {
+                       is_rwnd_limited = true;
                        break;
+               }
 
                if (tso_segs == 1) {
                        if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
@@ -2227,6 +2229,11 @@ repair:
                        break;
        }
 
+       if (is_rwnd_limited)
+               tcp_chrono_start(sk, TCP_CHRONO_RWND_LIMITED);
+       else
+               tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
+
        if (likely(sent_pkts)) {
                if (tcp_in_cwnd_reduction(sk))
                        tp->prr_out += sent_pkts;