From: Eric Dumazet <edumazet@google.com>
Date: Mon, 15 Sep 2014 11:19:51 +0000 (-0700)
Subject: tcp: use TCP_SKB_CB(skb)->tcp_flags in input path
X-Git-Tag: fixes-against-v3.18-rc2~81^2~56^2~2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e11ecddf5128011c936cc5360780190cbc901fdc;p=pandora-kernel.git

tcp: use TCP_SKB_CB(skb)->tcp_flags in input path

Input path of TCP do not currently uses TCP_SKB_CB(skb)->tcp_flags,
which is only used in output path.

tcp_recvmsg(), looks at tcp_hdr(skb)->syn for every skb found in receive queue,
and its unfortunate because this bit is located in a cache line right before
the payload.

We can simplify TCP by copying tcp flags into TCP_SKB_CB(skb)->tcp_flags.

This patch does so, and avoids the cache line miss in tcp_recvmsg()

Following patches will
- allow a segment with FIN being coalesced in tcp_try_coalesce()
- simplify tcp_collapse() by not copying the headers.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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