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

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Date:	Mon, 27 Apr 2015 22:37:18 +0200
From:	Pavel Machek <pavel@....cz>
To:	Pengfei Yuan <0xcoolypf@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Why not build kernel with -O3

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.

What is the size difference with -O3?

Do you have mostly-userspace benchmark? (kernel build?) -O3 could hurt there 
if it produces bigger code..
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
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