Re: [BENCHMARK] Corrected gcc3.2 v gcc2.95.3 contest results

Richard B. Johnson
2002-09-23T14:08:45Z

On Mon, 23 Sep 2002, Ryan Anderson wrote:

> On Mon, Sep 23, 2002 at 08:30:21PM +1000, Con Kolivas wrote:
> > Quoting Ingo Molnar <mingo@elte.hu>:
> > > On Mon, 23 Sep 2002, Con Kolivas wrote:
> > >
> > > how many times are you running each test? You should run them at least
> > > twice (ideally 3 times at least), to establish some sort of statistical
> > > noise measure. Especially IO benchmarks tend to fluctuate very heavily
> > > depending on various things - they are also very dependent on the initial
> > > state - ie. how the pagecache happens to lay out, etc. Ie. a meaningful
> > > measurement result would be something like:
> >
> > Yes you make a very valid point and something I've been stewing over privately
> > for some time. contest runs benchmarks in a fixed order with a "priming" compile
> > to try and get pagecaches etc back to some sort of baseline (I've been trying
> > hard to make the results accurate and repeatable).
>
> Well, run contest once, discard the results. Run it 3 more times, and
> you should have started the second, third and fourth runs with similar initial conditions.
>
> Or you could run the contest 3 times, rebooting between each run....
> (automating that is a little harder, of course.)
>
> IANAS, however.
>

(1) Obtain statistics from a number of runs.
(2) Throw away the smallest and largest.
(3) Average whatever remains.

This works for many "real-world" things because it removes noise-spikes
that could unfairly poison the average.

Cheers,
Dick Johnson
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