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SubjectRe: Why not build kernel with -O3
I am trying legacy GCC versions.
But I am not able to try different architectures.

2015-04-07 14:43 GMT+08:00 Mike Galbraith <umgwanakikbuti@gmail.com>:
> 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 ;-)
>
> -Mike


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