RFC: startup time - again

[Robert Collins]

On Fri, 2008-09-12 at 09:45 +0100, Russel Winder wrote:


> The so what about things not being stable is that to focus on a supposed
> 5% improvement when the variance is 10% is a waste of everybody's time.

Actually, its not. I made a very large improvement in commit performance
by a series of improvements, nearly every one of which was under the
variance of any set of runs.

Performance depends on two basic things:
 - doing as little work as possible
 - not waiting when work could be done

(the later point applies to networking, threading, etc)

If you run a workload ten times, once your caches are primed, each run
does the same work. So the lowest time indicates when you spent the
least time waiting when work could be done. Thus a small improvement
within the variance of the runs is still probably representative of less
work being done.

-Rob


-- 
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