linux-kernel - Why not build kernel with -O3

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Message-ID: <CACmZjJK8oLLFWBzUZpRTVrTycu8JDfd+hg6bBuxi-a8U6Hk_1A@mail.gmail.com>
Date:	Tue, 7 Apr 2015 11:37:27 +0800
From:	Pengfei Yuan <0xcoolypf@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: 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.

Why not add an option to build kernel with -O3?

Regards,
YUAN, Pengfei
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