Florian Westphal 31770e34e4 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>
2017-08-30 11:20:09 -07:00
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