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

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Message-ID: <20070821232320.GC29691@Krystal>
Date:	Tue, 21 Aug 2007 19:23:20 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Christoph Lameter <clameter@....com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com
Subject: Re: [PATCH] SLUB use cmpxchg_local

* Christoph Lameter (clameter@....com) wrote:
> On Tue, 21 Aug 2007, Mathieu Desnoyers wrote:
> 
> > - Changed smp_rmb() for barrier(). We are not interested in read order
> >   across cpus, what we want is to be ordered wrt local interrupts only.
> >   barrier() is much cheaper than a rmb().
> 
> But this means a preempt disable is required. RT users do not want that.
> Without preemption the processor can be moved after c has been determined.
> That is why the smp_rmb() is there.

preemption is required if we want to use cmpxchg_local anyway.

We may have to find a way to use preemption while being able to give an
upper bound on the preempt disabled execution time. I think I got a way
to do this yesterday.. I'll dig in my patches.

-- 
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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