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Re: 2% speedup with Duff's device

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Jarkko Hietaniemi
January 23, 2001 06:30
Re: 2% speedup with Duff's device
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On Tue, Jan 23, 2001 at 01:02:42PM +0000, Nick Ing-Simmons wrote:
> Nicholas Clark <> writes:
> >If one uses Duff's device in PERL_HASH, the regression tests go about 2%
> >faster.
> Note - that may be literally true, but is not the speed difference in perl.
> The tests are riddled with sleep()s and other system timing overhead.

That is true, the timing of the whole suite is to be taken with a
biiig grain of salt -- but a test of consisting of, say, 1 second of
actual test (CPU time being burned) and 1 second of sleep gets sped up
by, say, 10%, it means that the CPU time really got slashed by 20%,
which is actually *more* significant than without the sleep.

I think the most dubious element of the test suite as a whole is the
large number of separate and relatively small scripts, the operating
system (and filesystem, and networking, and ...) dependent startup
time may taint the results quite a lot.

$jhi++; #
        # There is this special biologist word we use for 'stable'.
        # It is 'dead'. -- Jack Cohen

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