linux-kernel - Re: [this_cpu_xx V5 19/19] SLUB: Experimental new fastpath w/o interrupt disable

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Message-ID: <alpine.DEB.1.10.0910071119450.9296@gentwo.org>
Date:	Wed, 7 Oct 2009 11:21:52 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Peter Zijlstra <peterz@...radead.org>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Tejun Heo <tj@...nel.org>, Mel Gorman <mel@....ul.ie>,
	mingo@...e.hu
Subject: Re: [this_cpu_xx V5 19/19] SLUB: Experimental new fastpath w/o
 interrupt disable

On Wed, 7 Oct 2009, Mathieu Desnoyers wrote:

> You are already calling the scheduler when ending the _fast_ path. I
> don't see the problem with calling it when you end the slow path
> execution.

Well yes that gives rise to the thought of using

	preempt_enable_no_sched()

at the end of the fastpath as well. Constant calls into the scheduler
could be a major performance issue. I dont notice it here since I usually
cannot affort the preempt overhead and build kernels without support for
it.


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