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

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Message-ID: <CACmZjJ+ZtfKWRjdt3FryViMix2M4r=OT=Tb9ntrU-P4T=vXNdQ@mail.gmail.com>
Date:	Wed, 8 Apr 2015 21:16:10 +0800
From:	Pengfei Yuan <0xcoolypf@...il.com>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Why not build kernel with -O3

2015-04-08 20:19 GMT+08:00 Richard Weinberger <richard.weinberger@...il.com>:
> 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.
>

This is really helpful.
But I can only find very short description for each option from
https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

> 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?

Redis is special among the six applications because it is single-threaded.

Yuan
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