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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>
This commit is contained in:
Francis Yan 2016-11-27 23:07:15 -08:00 committed by David S. Miller
parent 0f87230d1a
commit 5615f88614
1 changed files with 9 additions and 2 deletions
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11
net/ipv4/tcp_output.c
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@ -2144,7 +2144,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
unsigned int tso_segs, sent_pkts; unsigned int tso_segs, sent_pkts;
int cwnd_quota; int cwnd_quota;
int result; int result;
bool is_cwnd_limited = false; bool is_cwnd_limited = false, is_rwnd_limited = false;
u32 max_segs; u32 max_segs;
sent_pkts = 0; sent_pkts = 0;
@ -2181,8 +2181,10 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
break; 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; break;
}
if (tso_segs == 1) { if (tso_segs == 1) {
if (unlikely(!tcp_nagle_test(tp, skb, mss_now, if (unlikely(!tcp_nagle_test(tp, skb, mss_now,
@ -2227,6 +2229,11 @@ repair:
break; 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 (likely(sent_pkts)) {
if (tcp_in_cwnd_reduction(sk)) if (tcp_in_cwnd_reduction(sk))
tp->prr_out += sent_pkts; tp->prr_out += sent_pkts;