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

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Message-ID: <4D07A7CB.7010205@zytor.com>
Date:	Tue, 14 Dec 2010 09:22:19 -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 09:19 AM, Christoph Lameter wrote:
>>
>> 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.
> 
> Dropping the load increases the cycle count from 11 to 16.
> 

Great, that answers that!  I'll pick up the patch hopefully today (I'm
finally ramping back up on arch/x86 again after having been diverted to
an internal project for a while...)

	-hpa

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

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