time resolution in Neal nelson benchmark

Peter Brouwer pb at idca.tds.PHILIPS.nl
Mon Sep 18 17:59:24 AEST 1989

In the discussion on which benchmarks to use as a reaction on a comparison
done on machines by a unix magazin , neal nelson was mentioned as a benchmark
to use.
I have two points of comments on this bench mark.
Some month back we used neal nelson benchmarks to compare machines.
When i looked at the sources I saw that the time of the tests are measured
with the system call time, so resolution is in seconds. This makes the fast
tests on fast machines inacurate. I test that runs in 10 sec has an 
accuracy of 10%. This has to be thought of when looking at machine comparisons.

An other remark I have is that all runs ( for n copies of the test ) run
paralel. ( For those who are not familiar with neal neson bench mark,
a number of runs can be executed paralel, each run consists of a 
series of tests that are executed in a fixed sequence. )
This means that the code of that test will fit in the system cache.
The cache hit ratio will be high. This is not an realistic situation on
a multi user machine.
It would be better to make the order of the tests random for each or a number
of copies of a run. The musbus benchmark does something like this. It
created a number of execution scripts from a master script. Each script
executes the test from the master script in a different order.
Peter Brouwer,                # Philips Telecommunications and Data Systems,
NET  : pb at idca.tds.philips.nl # Department SSP-P9000 Building V2,
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PHONE:ext [+31] [0]55 432523, # Never underestimate the power of human stupidity

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