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

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Date:	Tue, 07 Apr 2015 10:07:13 +0300
From:	Boaz Harrosh <boaz@...xistor.com>
To:	Mike Galbraith <umgwanakikbuti@...il.com>,
	Pengfei Yuan <0xcoolypf@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Why not build kernel with -O3

On 04/07/2015 09:43 AM, Mike Galbraith wrote:
> On Tue, 2015-04-07 at 11:37 +0800, Pengfei Yuan wrote:
>> Hi,
>>
>> I have conducted some experiments to compare kernels built with -O2
>> and -O3. Here are the results:
>>
>> Application  Performance O2   Performance O3   Improvement
>> Apache       127814.14 req/s  130321.24 req/s  1.96%
>> Nginx        537589.08 req/s  556723.32 req/s  3.56%
>> MySQL        70661.38 tx/s    71008.47 tx/s    0.49%
>> PostgreSQL   79763.39 tx/s    79535.59 tx/s    -0.29%
>> Redis        352547.47 op/s   405417.24 op/s   15.0%
>> Memcached    844439.14 op/s   845321.79 op/s   0.10%
>>
>> Geomean: +3.34%
>>
>> Experiment environment: Linux 3.19.3, GCC 4.9.3 prerelease, Core-i7
>> 4770, 32G RAM, 10GbE
>>
>> LMbench microbenchmark also shows reduction in various latencies, as
>> well as increase of throughputs.
> 
> Please show multiple run data for all permutations of supported gcc 
> version/arch ;-)
> 

He did say optional. So I'd imagine it would be a Kconfig of its own.
So the default can be as today, but people that want to experiment
need not hack the source code.

Cheers
Boaz

>         -Mike


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