From: Neal Cardwell <ncardwell@google.com>
To: David Miller <davem@davemloft.net>
Cc: edumazet@google.com, ycheng@google.com, nanditad@google.com,
netdev@vger.kernel.org, Neal Cardwell <ncardwell@google.com>
Subject: [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path
Date: Mon, 4 Mar 2013 11:23:05 -0500 [thread overview]
Message-ID: <1362414185-9874-1-git-send-email-ncardwell@google.com> (raw)
We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
before and after going to step5. That wastes CPU and double-counts the
receiver-side RTT sample.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
---
net/ipv4/tcp_input.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a759e19..0d9bdac 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5485,6 +5485,9 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
if (tcp_checksum_complete_user(sk, skb))
goto csum_error;
+ if ((int)skb->truesize > sk->sk_forward_alloc)
+ goto step5;
+
/* Predicted packet is in window by definition.
* seq == rcv_nxt and rcv_wup <= rcv_nxt.
* Hence, check seq<=rcv_wup reduces to:
@@ -5496,9 +5499,6 @@ int tcp_rcv_established(struct sock *sk, struct sk_buff *skb,
tcp_rcv_rtt_measure_ts(sk, skb);
- if ((int)skb->truesize > sk->sk_forward_alloc)
- goto step5;
-
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
/* Bulk data transfer: receiver */
--
1.8.1.3
next reply other threads:[~2013-03-04 16:52 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-03-04 16:23 Neal Cardwell [this message]
2013-03-04 16:55 ` [PATCH net] tcp: fix double-counted receiver RTT when leaving receiver fast path Eric Dumazet
2013-03-04 19:16 ` David Miller
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