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

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Message-ID: <alpine.DEB.1.00.0910131550050.15347@chino.kir.corp.google.com>
Date:	Tue, 13 Oct 2009 15:53:00 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux-foundation.org>
cc:	Pekka Enberg <penberg@...helsinki.fi>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Mel Gorman <mel@....ul.ie>,
	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

On Tue, 13 Oct 2009, Christoph Lameter wrote:

> > For an optimized fastpath, I'd expect such a workload would result in at
> > least a slightly higher transfer rate.
> 
> There will be no improvements if the load is dominated by the
> instructions in the network layer or caching issues. None of that is
> changed by the path. It only reduces the cycle count in the fastpath.
> 

Right, but CONFIG_SLAB shows a 5-6% improvement over CONFIG_SLUB in the 
same workload so it shows that the slab allocator does have an impact in 
transfer rate.  I understand that the performance gain with this patchset, 
however, may not be representative with the benchmark since it also 
frequently uses the slowpath for kmalloc-256 about 25% of the time and the 
added code of the irqless patch may mask the fastpath gain.
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