commit 31770e34e43d6c8dee129bfee77e56c34e61f0e5
author Florian Westphal <fw@strlen.de> Wed Aug 30 19:24:58 2017 +0200
committer David S. Miller <davem@davemloft.net> Wed Aug 30 11:20:09 2017 -0700
tree a4635a632732b39ef560a8f72eb3a81d04f01605
parent c1d2b4c3e204e602c97680335d082b8d012d08cd

tcp: Revert "tcp: remove header prediction"

This reverts commit 45f119bf936b1f9f546a0b139c5b56f9bb2bdc78.

Eric Dumazet says:
  We found at Google a significant regression caused by
  45f119bf936b1f9f546a0b139c5b56f9bb2bdc78 tcp: remove header prediction

  In typical RPC  (TCP_RR), when a TCP socket receives data, we now call
  tcp_ack() while we used to not call it.

  This touches enough cache lines to cause a slowdown.

so problem does not seem to be HP removal itself but the tcp_ack()
call.  Therefore, it might be possible to remove HP after all, provided
one finds a way to elide tcp_ack for most cases.

Reported-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>