Some tips for benchmarking

[David Blaikie via llvm-commits]

(might be worth mentioning on llvm-dev - could get lost on commits)

Maybe even writing up as documentation on the website somewhere - runtime
analysis has always been a real pain for me to get reliable numbers, so I'm
really glad for any/all tips I can find when I end up dealing with it.

On Wed, Oct 19, 2016 at 7:39 PM Rafael Espíndola via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> After much pain I decided that instead of just running tests many
> times I should put some effort in figuring out why perf numbers were
> so hard to reproduce on my machine.
>
> I was already disabling address space randomization and setting the
> scaling_governor to performance. Other things I found
>
> * Use https://github.com/lpechacek/cpuset to reserve a cpu for just
> the program you are benchmarking.
> * Disable the SMP pair (echo 0 > /sys/devices/system/cpu/cpuX/online)
> of the cpu you will use for the benchmark.
> * disable turbo mode (echo 1 >
> /sys/devices/system/cpu/intel_pstate/no_turbo).
>
> The results are pretty awesome:
>
> 3.012355647 seconds time elapsed         ( +-  0.01% )
>
> :-)
>
> Cheers,
> Rafael
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