netdev - Re: [PATCH net-next] net: avoid two atomic operations in fast clones

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Message-Id: <20141209.134039.1896885552629089445.davem@davemloft.net>
Date:	Tue, 09 Dec 2014 13:40:39 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, clm@...com, sd@...asysnail.net,
	subramanian.vijay@...il.com
Subject: Re: [PATCH net-next] net: avoid two atomic operations in fast
 clones

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 03 Dec 2014 17:04:39 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Commit ce1a4ea3f125 ("net: avoid one atomic operation in skb_clone()")
> took the wrong way to save one atomic operation.
> 
> It is actually possible to avoid two atomic operations, if we
> do not change skb->fclone values, and only rely on clone_ref
> content to signal if the clone is available or not.
> 
> skb_clone() can simply use the fast clone if clone_ref is 1.
> 
> kfree_skbmem() can avoid the atomic_dec_and_test() if clone_ref is 1.
> 
> Note that because we usually free the clone before the original skb,
> this particular attempt is only done for the original skb to have better
> branch prediction.
> 
> SKB_FCLONE_FREE is removed.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks.
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