linux-kernel - Re: Why not build kernel with -O3

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Date:	Wed, 08 Apr 2015 08:49:14 -0400
From:	Austin S Hemmelgarn <ahferroin7@...il.com>
To:	Richard Weinberger <richard.weinberger@...il.com>,
	Pengfei Yuan <0xcoolypf@...il.com>
CC:	Mike Galbraith <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Why not build kernel with -O3

On 2015-04-08 08:19, Richard Weinberger wrote:
> On Wed, Apr 8, 2015 at 3:00 AM, Pengfei Yuan <0xcoolypf@...il.com> wrote:
>> Could you please provide some examples that I can investigate?
>> Thanks!
>
> It would be awesome if you could find out which gcc optimizations
> cause the speed up.
> "gcc -c -Q -O3 --help=optimizers" will help you.
>
> Please also double check your results.
> You need do to multiple runs, etc...
> Especially the redis speed up looks odd. Does redis really spend that much time
> in the kernel?
>
My guess would be that much of the speed up is actually related to 
context switch handling and the scheduling/statistics related code.


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