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Re: our benchmark-suite
From: |
Andy Wingo |
Subject: |
Re: our benchmark-suite |
Date: |
Wed, 16 May 2012 19:01:49 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/23.4 (gnu/linux) |
Howdy!
On Wed 25 Apr 2012 22:39, address@hidden (Ludovic Courtès) writes:
>> So, those are the problems: benchmarks running for inappropriate,
>> inconsistent durations;
>
> I don’t really see such a problem. It doesn’t matter to me if
> ‘arithmetic.bm’ takes 2mn while ‘vlists.bm’ takes 40s, since I’m not
> comparing them.
Running a benchmark for 2 minutes is not harmful to the results, but it
is a bit needless. One second is enough.
However, running a benchmark for just a few milliseconds is not very
interesting:
;; ("if.bm: if-<bool>-then: executing then" 330000 real 0.011994627
real/iteration 3.63473545454545e-8 run/iteration 3.62829060606061e-8
core/iteration 9.61427360606058e-10 gc 0.0)
That's 12 milliseconds. The jitter there is too much.
>> inappropriate benchmarks;
>
> I agree that things like ‘if.bm’ are not very relevant now. But there
> are also appropriate benchmarks, and benchmarks are always better than
> wild guess. ;-)
Agreed :-)
>> and benchmarks being optimized out.
>
> That should be fixed.
In what way? It would make those benchmarks different.
Thesis: anything for which you would want to turn off the optimizer is
not a good benchmark anyway.
See also: http://www.azulsystems.com/presentations/art-of-java-benchmarking
>> My proposal is to rebase the iteration count in 0-reference.bm to run
>> for 0.5s on some modern machine, and adjust all benchmarks to match,
>> removing those benchmarks that do not measure anything useful.
>
> Sounds good. However, adjusting iteration counts of the benchmarks
> themselves should be done rarely, as it breaks performance tracking like
> <http://ossau.homelinux.net/~neil/bm_master_i.html>.
I think we've established that this isn't the case -- modulo the effect
that such a change would have on GC (process image size, etc)
>> Finally we should perhaps enable automatic scaling of the iteration
>> count. What do folks think about that?
>>
>> On the positive side, all of our benchmarks are very clear that they are
>> a time per number of iterations, and so this change should not affect
>> users that measure time per iteration.
>
> If the reported time is divided by the global iteration count, then
> automatic scaling of the global iteration count would be good, yes.
OK, will do.
Speak now or be surprised by a commit!
;-)
Andy
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