Re: our benchmark-suite

[Andy Wingo <wingo@pobox.com>]

Howdy!

On Wed 25 Apr 2012 22:39, ludo@gnu.org (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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