[LLVMdev] Use perf tool for more accurate time measuring on Linux

[Tobias Grosser]

On 20/05/2014 16:01, Yi Kong wrote:
> I've set up a public LNT server to show the result of perf stat. There
> is a huge improvement compared with timeit tool.
> http://parkas16.inria.fr:8000/

Hi Yi Kong,

thanks for testing these changes.

> Patch is updated to pin the process to a single core, the readings are
> even more accurate. It's hard coded to run everything on core 0, so
> don't run parallel testing with it for now. The tool now depends on
> Linux perf and schedtool.

I think this sounds like a very good direction.

How did you evaluate the improvements exactly? The following run shows 
e.g two execution time changes:

http://parkas16.inria.fr:8000/db_default/v4/nts/9

Are they expected? If I change e.g. the aggregation function to median
they disappear. Similarly the graph for one of them does not suggest an 
actual performance change:

http://parkas16.inria.fr:8000/db_default/v4/nts/graph?show_all_points=yes&moving_window_size=10&plot.0=1.428.3&submit=Update

Cheers,
Tobias