linux-kernel - Re: [PATCH 0/3] Reduce length of the eagerfpu path during x86 context switches

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Date:	Wed, 27 Aug 2014 10:03:02 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mel Gorman <mgorman@...e.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Mike Galbraith <mgalbraith@...e.de>, Linux-X86 <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Reduce length of the eagerfpu path during x86 context
 switches

On 08/27/2014 09:03 AM, Mel Gorman wrote:
> On Wed, Aug 06, 2014 at 01:55:45PM +0100, Mel Gorman wrote:
>> Eager FPU switching is used on CPUs that support xsave on the grounds
>> that CPUs that support it can optimise the switch with xsaveopt and xrstor
>> instead of serialising by updating cr0.TS which has serialising semantics.
>>
>> The path for eagerfpu is fatter than it needs to be because it still
>> maintains the fpu_counter for lazy FPU switches even though the information
>> is never used. This patch splits the paths optimises the eagerfpu path a
>> little. The benefit is marginal, it was just noticed when looking at why
>> integer-only workloads were spending time saving/restoring FPU states.
>>
> 
> This was initially sent when it would collide with the merge window
> which was stupid timing. Nothing has actually changed since but I wonder
> if anyone had a chance to take a look at this patches?
> 

Looking at it now.

	-hpa


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