netdev - Re: [PATCH 1/3] skb: Drop bad code from pskb_expand

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Date:	Sun, 06 May 2012 13:13:37 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	alexander.h.duyck@...el.com, netdev@...r.kernel.org,
	jeffrey.t.kirsher@...el.com
Subject: Re: [PATCH 1/3] skb: Drop bad code from pskb_expand_head

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 05 May 2012 07:35:30 +0200

> On Fri, 2012-05-04 at 17:26 -0700, Alexander Duyck wrote:
>> The fast-path for pskb_expand_head contains a check where the size plus the
>> unaligned size of skb_shared_info is compared against the size of the data
>> buffer.  This code path has two issues.  First is the fact that after the
>> recent changes by Eric Dumazet to __alloc_skb and build_skb the shared info
>> is always placed in the optimal spot for a buffer size making this check
>> unnecessary.  The second issue is the fact that the check doesn't take into
>> account the aligned size of shared info.  As a result the code burns cycles
>> doing a memcpy with nothing actually being shifted.
>> 
>> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
 ...
> Acked-by: Eric Dumazet <edumazet@...gle.com>

Applied.

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