From: Eric Dumazet <edumazet@google.com>
Date: Mon, 29 Sep 2014 05:18:47 +0000 (-0700)
Subject: net: reorganize sk_buff for faster __copy_skb_header()
X-Git-Tag: omap-for-v3.19/prcm-cleanup~141^2~116
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b1937227316417aa7568d01e6fa1f272e98fb890;p=pandora-kernel.git

net: reorganize sk_buff for faster __copy_skb_header()

With proliferation of bit fields in sk_buff, __copy_skb_header() became
quite expensive, showing as the most expensive function in a GSO
workload.

__copy_skb_header() performance is also critical for non GSO TCP
operations, as it is used from skb_clone()

This patch carefully moves all the fields that were not copied in a
separate zone : cloned, nohdr, fclone, peeked, head_frag, xmit_more

Then I moved all other fields and all other copied fields in a section
delimited by headers_start[0]/headers_end[0] section so that we
can use a single memcpy() call, inlined by compiler using long
word load/stores.

I also tried to make all copies in the natural orders of sk_buff,
to help hardware prefetching.

I made sure sk_buff size did not change.

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