[CSC 435] CSC 435 Hybrid Question

[Andrew J. Pounds]

So there are ALL KINDS OF THINGS that can go wrong if you play with the
indexing of a hybrd MPI/OpenMP program.  If you are getting the correct
trace of the matrix (which should equal the dimension of the matrix) for
dimensions of like 4313 (and not just dimensions that are evenly
divisible by the number of threads) then you can generally say with
confidence that you are getting accurate results with your hybrid strategy.

The problem that you may face is that the techniques you take to
guarantee that you are getting correct results may impact your
parallelism -- as there are regions to be threaded in both the RANK=0
and RANK!=0 portions of the code.   If you simply demonstrate that your
hybrid parallelism gives the expected result and that you get improved
performance when you to move to more threads and nodes, then you have
accomplished the goal.

There are MANY things that can hinder this and I am not expecting any of
you to achieve a linear speedup.  To do that we have would have to dive
MUCH DEEPER into inter-process locality, processor affinities, and
processor binding.  Those are things I teach in the graduate version of
this course.

I set the bar pretty low -- but it is still a bar to get over.  Can you
achieve any speedup with correct results when employing you hybrid
parallel strategy?

On 4/26/20 6:52 PM, wrote:
> Dr. Pounds,
>
> How should we demonstrate that we are getting accurate results?
> Include the pbs resultant files in an appendix? It feels kind of
> circular to say "let me demonstrate my results are accurate", and then
> say "Ok I checked and they are." From my results I can see that the
> accuracy is evident, but I don't know a good way to demonstrate that
> to my audience. Thanks.
>
>

-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Director of the Computational Science Program
Mercer University,  Macon, GA 31207   (478) 301-5627

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