linux-kernel - Re: [this_cpu_xx V7 6/8] Make slub statistics use this_cpu

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Date:	Tue, 15 Dec 2009 15:59:36 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
CC:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Mel Gorman <mel@....ul.ie>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [this_cpu_xx V7 6/8] Make slub statistics use this_cpu_inc

Le 15/12/2009 15:46, Christoph Lameter a écrit :
> On Tue, 15 Dec 2009, Eric Dumazet wrote:
> 
>> Le 14/12/2009 23:03, Christoph Lameter a écrit :
>>> this_cpu_inc() translates into a single instruction on x86 and does not
>>> need any register. So use it in stat(). We also want to avoid the
>>> calculation of the per cpu kmem_cache_cpu structure pointer. So pass
>>> a kmem_cache pointer instead of a kmem_cache_cpu pointer.
>>>
>>
>> Hmm, last time I checked, [__]this_cpu_inc were not using "inc" on x86,
>> but the default [__]this_cpu_add((pcp), 1)
> 
> Well the add 1 is still a single instruction so its okay. We can easily
> add support for inc on x86 if makes a difference?
> 

Probably not, only one byte of text per use can be saved.

Sorry, rereading your changelog I dont know why I thought about "inc" instruction.

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