linux-kernel - Re: [x86] Fix prefetch instruction

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Message-ID: <4E3C4EF1.3040709@zytor.com>
Date:	Fri, 05 Aug 2011 13:13:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [x86] Fix prefetch instruction

On 08/05/2011 09:18 AM, Christoph Lameter wrote:
> The prefetchnta instruction used for prefetching on x86 is a special instruction
> used for streaming that is usually used to avoid polluting the l2 and l3 caches.
> The cacheline will be evicted rapidly.
> 
> What we need is a prefetch that puts the cacheline in all levels of the cache hierachy instead.
> Change the instruction to do that.
> 
> Acked-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Christoph Lameter <cl@...ux.com>
> 

Have you done any performance analysis on this versus the null case?  I
know there are some workloads where it helps, but if it hurts as many as
it helps...

	-hpa

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