[OT] Maximum performance on single processor ?

John Hearns jhearns at freesolutions.net
Fri Jun 20 09:01:45 EDT 2003


>
> Right now, even on simple test cases, the "response time" (eg calculation
> time for a single step) of our program is on the order of the second.
> (this is for an athlon MP 2600+)
> We need to get that down to a fraction of seconds, best milli-seconds,
> in order to be usable in real time. (makes it a factor of roughly 1000)
>
> As I said the code can indeed be parallelized - maybe even simply cleaned
> up in some parts - but unfortunately there remains very much other
important
> stuff to do. So we'd rather spend some money on a really fast CPU and not
> touch the code at the moment.

I disagree. You really must do some code profiling.
You may find some real big bottleneck, which is either unintentional or not
necessary.

Also, you should consider how the code is written - if you are manipulating
large
arrays then the order of access, and the stride length can make a big
difference.
You may be ranging all over a huge array, pulling things in from memory(*)
when
a different algorithm/different loop arrangement could keep things in cache.
And Fortran, being 'closer to the machine' can expose these things (I may be
wrong).
Have you looked at books like:
"High Performance Computing" http://www.oreilly.com/catalog/hpc2/



(*) Sorry to teach my granny to suck eggs, but your machine isn't going into
swap I trust.

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