linux-kernel - Re: [PATCH 1/1] x86_64: add config options to optimize for newer AMD processors

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Date:	Sun, 29 Sep 2013 16:41:02 -0400
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Linux-Kernel mailing list <linux-kernel@...r.kernel.org>,
	Linux Torvalds <torvalds@...l.org>, Alan Cox <alan@...hat.com>
Subject: Re: [PATCH 1/1] x86_64: add config options to optimize for newer
 AMD processors

On 09/29/2013 02:01 PM, Borislav Petkov wrote:
> On Sun, Sep 29, 2013 at 01:54:00PM -0400, Austin S Hemmelgarn
> wrote:
>> From: Austin S. Hemmelgarn <ahferroin7@...il.com>
>> 
>> This patch adds Kconfig options to allow optimization for AMD
>> family 10h, AMD Bulldozer, and AMD Piledriver derived CPU's in
>> version 3.12-rc2.  These provide noticeable improvements over the
>> K8 config option, and allow the kernel to take full advantage of
>> AMD specific instruction set extensions, such as ABM, LZCNT, and
>> POPCNT.
> 
> A patch like that keeps popping up every couple of months. Please
> show us those noticeable improvements because the guy last time
> failed to do so.
> 
> And also, keep in mind that distro kernels are built with 
> CONFIG_GENERIC_CPU so CPU-specific kernels are used only by the
> small percentage of people who actually do build their own
> kernels.
> 
> Thanks.
> 
While I understand that you want decisive proof that it provides an
improvement, does it specifically matter if the option is unused by
most people and doesn't result in a negative performance hit when used?

I will, however, do some intensive profiling over the next week and
get back to you about exact improvements.  Just in the past few days
of using it, I have noticed much better response time in time
sensitive user-space code (mostly emulators and multimedia apps).
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