Re: [PATCH] rmap 14

["Stephen C. Tweedie" <sct@redhat.com>]

Hi,

On Mon, Aug 19, 2002 at 10:04:19PM +0100, Mel wrote:

> > That's exactly the concern that I had.  Large timing result like that are
> > more likely because your code was preempted for something else.  It would
> > probably be good to do *something* about these statistical outliers,
> > because they can affect averages substantially.
> 
> At the moment I'm not calculating averages and I haven't worked out the
> best way to factor in large skews in page reads. For the moment, I'm
> taking the easy option and depending on the tester to be able to ignore
> the bogus data.

You can get that by a bit of stats: keeping track of the sum of each
value you observe plus their squares and cubes gives you the main
stats you probably want to collect:

	mean			(obvious)
	standard deviation 	(measures variation between samples)
	standard error		(shows how accurate your estimation of
				 the mean is)
and	skew/3rd-moment		(shows how one-sided the distribution
				 is)

Distributions with a long tail to one side will have a high skew.  The
main one is standard error, though --- without that you have no idea
how useful your results are.

--Stephen
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