linux-kernel - Re: [cpuops cmpxchg V2 5/5] cpuops: Use cmpxchg for xchg to avoid lock semantics

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Message-ID: <4D07A2B7.8080405@zytor.com>
Date:	Tue, 14 Dec 2010 09:00:39 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Eric Dumazet <eric.dumazet@...il.com>, Tejun Heo <tj@...nel.org>,
	akpm@...ux-foundation.org, Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [cpuops cmpxchg V2 5/5] cpuops: Use cmpxchg for xchg to avoid
 lock semantics

On 12/14/2010 08:55 AM, Christoph Lameter wrote:
> 
> We do not need to reload the value as pointed out by Eric. It is already in
> the correct register so just rerun the cmpxchg without the load.
> 
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 

Is it genuinely faster to do the pre-load mov, or can we drop that too?
 My guess would be that yes it is, but if it happens not to be it would
be nice to reduce the code size.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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