[ 61/75] tcp: fix double-counted receiver RTT when leaving receiver fast path

Greg Kroah-Hartman
2013-03-18T21:07:21Z

From: Neal Cardwell <ncardwell@google.com>

[ Upstream commit aab2b4bf224ef8358d262f95b568b8ad0cecf0a0 ]

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>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_input.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5498,6 +5498,9 @@ int tcp_rcv_established(struct sock *sk,
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:
@@ -5509,9 +5512,6 @@ int tcp_rcv_established(struct sock *sk,

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 */