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

[Richard B. Johnson]

On Mon, 23 Sep 2002, Ryan Anderson wrote:

> On Mon, Sep 23, 2002 at 08:30:21PM +1000, Con Kolivas wrote:
> > Quoting Ingo Molnar <[e-mail]>:
> > > 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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