[llvm-dev] Noisy benchmark results?

[Mikael Holmén via llvm-dev]

Hi,

I'm trying to run the benchmark suite:
  http://llvm.org/docs/TestingGuide.html#test-suite-quickstart

I'm doing it the lnt way, as described at:
  http://llvm.org/docs/lnt/quickstart.html

I don't know what to expect but the results seems to be quite noisy and 
unstable. E.g I've done two runs on two different commits that only 
differ by a space in CODE_OWNERS.txt on my 12 core ubuntu 14.04 machine 
with:

  lnt runtest nt --sandbox SANDBOX --cc <path-to-my-clang> --test-suite 
/data/repo/test-suite -j 8

And then I get the following top execution time regressions:
  http://i.imgur.com/sv1xzlK.png

The numbers bounce around a lot if I do more runs.

Given the amount of noise I see here I don't know to sort out 
significant regressions if I actually do a real change in the compiler.

Are the above results expected?

How to use this?


As a bonus question, if I instead run the benchmarks with an added -m32:
  lnt runtest nt --sandbox SANDBOX --cflag=-m32 --cc <path-to-my-clang> 
--test-suite /data/repo/test-suite -j 8

I get three failures:

--- Tested: 2465 tests --
FAIL: MultiSource/Applications/ClamAV/clamscan.compile_time (1 of 2465)
FAIL: MultiSource/Applications/ClamAV/clamscan.execution_time (494 of 2465)
FAIL: 
MultiSource/Benchmarks/DOE-ProxyApps-C/XSBench/XSBench.execution_time 
(495 of 2465)

Is this known/expected or do I do something stupid?

Thanks,
Mikael