linux-kernel - Re: [PATCH] SLUB use cmpxchg

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Date:	Mon, 27 Aug 2007 17:10:03 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Christoph Lameter <clameter@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com
Subject: Re: [PATCH] SLUB use cmpxchg_local

* Christoph Lameter (clameter@....com) wrote:
> I think the simplest solution may be to leave slub as done in the patch 
> that we developed last week. The arch must provide a cmpxchg_local that is 
> performance wise the fastest possible. On x86 this is going to be the 
> cmpxchg_local on others where cmpxchg is slower than interrupt 
> disable/enable this is going to be the emulation that does
> 
> interrupt disable
> 
> cmpchg simulation
> 
> interrupt enable
> 
> 
> If we can establish that this is not a performance regression then we have 
> a clean solution source code wise. It also minimizes the interrupt holdoff 
> for the non-cmpxchg_local arches. However, it means that we will have to 
> disable interrupts twice for the slow path. If that is too expensive then 
> we need a different solution.
> 

cmpxchg_local is not used on the slow path... ?

Did you meant:

it means that we will have to disable preemption _and_ interrupts on the
fast path for non-cmpxchg_local arches ?

Or maybe am I thinking about the wrong code snippet there ?

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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