Why not build kernel with -O3

From: Pengfei Yuan
Date: Mon Apr 06 2015 - 23:37:54 EST


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?

YUAN, Pengfei
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