linux-kernel - Re: [this_cpu_xx V6 7/7] this_cpu: slub aggressive use of this

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Date:	Wed, 14 Oct 2009 10:08:12 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>
Subject: Re: [this_cpu_xx V6 7/7] this_cpu: slub aggressive use of this_cpu
 operations in the hotpaths

The test did not include the irqless patch I hope?

On Wed, 14 Oct 2009, Mel Gorman wrote:

> Small gains in the User, System and Elapsed times with this-cpu patches
> applied. It is interest to note for the mean times that the patches more
> than close the gap between SLUB and SLAB for the most part - the
> exception being User which has marginally better performance. This might
> indicate that SLAB is still slightly better at giving back cache-hot
> memory but this is speculation.

The queuing in SLAB allows a better cache hot behavior. Without a queue
SLUB has a difficult time improvising cache hot behavior based on objects
restricted to a slab page. Therefore the size of the slab page will
affect how much "queueing" SLUB can do.

> The patches mostly improve the performance of netperf UDP_STREAM by a good
> whack so the patches are a plus here. However, it should also be noted that
> SLAB was mostly faster than SLUB, particularly for large packet sizes. Refresh
> my memory, how do SLUB and SLAB differ in regards to off-loading large
> allocations to the page allocator these days?

SLUB offloads allocations > 8k to the page allocator.
SLAB does create large slabs.

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