releases/3.8.4/tcp-fix-double-counted-receiver-rtt-when-leaving-receiver-fast-path.patch

   1 From 2d2809452253a92adcabba4d897bf58a5c9794fb Mon Sep 17 00:00:00 2001
   2 From: Neal Cardwell <ncardwell@google.com>
   3 Date: Mon, 4 Mar 2013 06:23:05 +0000
   4 Subject: tcp: fix double-counted receiver RTT when leaving receiver fast path
   5
   6
   7 From: Neal Cardwell <ncardwell@google.com>
   8
   9 [ Upstream commit aab2b4bf224ef8358d262f95b568b8ad0cecf0a0 ]
  10
  11 We should not update ts_recent and call tcp_rcv_rtt_measure_ts() both
  12 before and after going to step5. That wastes CPU and double-counts the
  13 receiver-side RTT sample.
  14
  15 Signed-off-by: Neal Cardwell <ncardwell@google.com>
  16 Acked-by: Eric Dumazet <edumazet@google.com>
  17 Signed-off-by: David S. Miller <davem@davemloft.net>
  18 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  19 ---
  20  net/ipv4/tcp_input.c |    6 +++---
  21  1 file changed, 3 insertions(+), 3 deletions(-)
  22
  23 --- a/net/ipv4/tcp_input.c
  24 +++ b/net/ipv4/tcp_input.c
  25 @@ -5498,6 +5498,9 @@ int tcp_rcv_established(struct sock *sk,
  26                                 if (tcp_checksum_complete_user(sk, skb))
  27                                         goto csum_error;
  28
  29 +                               if ((int)skb->truesize > sk->sk_forward_alloc)
  30 +                                       goto step5;
  31 +
  32                                 /* Predicted packet is in window by definition.
  33                                  * seq == rcv_nxt and rcv_wup <= rcv_nxt.
  34                                  * Hence, check seq<=rcv_wup reduces to:
  35 @@ -5509,9 +5512,6 @@ int tcp_rcv_established(struct sock *sk,
  36
  37                                 tcp_rcv_rtt_measure_ts(sk, skb);
  38
  39 -                               if ((int)skb->truesize > sk->sk_forward_alloc)
  40 -                                       goto step5;
  41 -
  42                                 NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPHITS);
  43
  44                                 /* Bulk data transfer: receiver */