[Beowulf] cluster softwares supporting parallel CFD computing

Patrick Geoffray patrick at myri.com
Thu Sep 14 21:42:16 PDT 2006

Hi Mark,

Mark Hahn wrote:
> all these points are accurate to some degree, but give a sad impression
> of the typical MPI programmer.  how many MPI programmers are professionals,
> rather than profs or grad students just trying to finish a calculation?
> I don't know, since I only see the academic side.

I think that the sample of MPI codes or traces that I have seen so far 
is a good representation of the academic, labs and commercial sides. 
It's pretty bad. I am sure they are many reasons, but a few come to mind:

* a lot of codes in academia and at the labs are written directly by the 
scientist, physicist, chemist, whatever. They are expert in their 
domain, but they don't know how to write good code. Doesn't matter if 
it's parallel or sequential, they don't know how to do it right. For 
their defense, they never really learned, and they are doing the best 
they can. However, they really should work with professional 
programmers. It's paradoxical that physicists would use the service of a 
statistician to help them make sense of their experimental data, but 
they don't want help for computer science.
It's interesting to note that there has always been this push from high 
in the food chain to bypass the human computer science expertise: it was 
automagic compilers (OpenMP, HPF and family) in the past, it's 
"high-productivity" languages now.

* In the commercial side, the codes are quite old, at least in their 
design. You can see traces of port from SHMEM to MPI, with Barriers 
a-lot-and-often. You see collective communications done by hand, I guess 
because the implementation of the collectives sucked at the time. You 
see an shameful amount of unexpected messages, the kind where the 
receive is just a little too late, typical from a code that was designed 
for a slow network, relatively. In short, it looks like they minimize 
the investment in code maintenance.

> for academics, time-to-publish is the main criterion, which doesn't 
> necessarily mean well-designed or tuned code.  taking a significant 

I don't know if time is really the constraint here. For grads students, 
sure, but I would not think that more time would help with profs. A good 
programing book maybe, but they are too proud to read those :-)

Patrick Geoffray
Myricom, Inc.

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