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

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Message-ID: <Pine.LNX.4.64.0708211612580.6062@schroedinger.engr.sgi.com>
Date:	Tue, 21 Aug 2007 16:14:19 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com
Subject: Re: [PATCH] SLUB use cmpxchg_local

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.
-
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