netdev - Re: [PATCH net-next] net: reorganize sk_buff for faster __copy_skb

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Message-Id: <20140928.173759.584339934179620924.davem@davemloft.net>
Date:	Sun, 28 Sep 2014 17:37:59 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, amirv@...lanox.com,
	john.r.fastabend@...el.com, brouer@...hat.com
Subject: Re: [PATCH net-next] net: reorganize sk_buff for faster
 __copy_skb_header()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Thu, 25 Sep 2014 14:20:04 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> 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@...gle.com>

Applied, thanks!
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