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Re: our benchmark-suite

From: Ludovic Courtès
Subject: Re: our benchmark-suite
Date: Wed, 25 Apr 2012 22:39:33 +0200
User-agent: Gnus/5.110018 (No Gnus v0.18) Emacs/24.0.93 (gnu/linux)

Hi Andy!

Andy Wingo <address@hidden> skribis:

> For what it's worth, the current overhead of the benchmark appears to be
> about 35 microseconds per iteration, on my laptop.  If we inline the
> iteration into the benchmark itself, rather than calling a thunk
> repeatedly, we can bring that down to around 13 microseconds.

There are a few benchmarks doing it already.  See, for instance,
‘repeat’ in ‘’.

> 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
‘’ takes 2mn while ‘’ takes 40s, since I’m not
comparing them.

> inappropriate benchmarks;

I agree that things like ‘’ are not very relevant now.  But there
are also appropriate benchmarks, and benchmarks are always better than
wild guess.  ;-)

> and benchmarks being optimized out.

That should be fixed.

> My proposal is to rebase the iteration count in 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

> 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.


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