[Beowulf] multi-threading vs. MPI

[Galen Arnold]

Gerry,

> Debates and differences aside, often-times, this forum *is* an authoritative 
> source of information.
>

Indeed it is.

By the way, we've got an old-ish course on multilevel 
parallel programming at ci-tutor.ncsa.uiuc.edu in case anybody wants to go 
there and see what people were thinking a couple years ago when they wrote 
it.

I've seen the benchmark speedups with mixed-mode as well.  With the right 
code, on a day with the wind to your back, threads can make good use of 
communication induced idle time on a node [yeah MPI supports overlap...
that's more difficult to achieve than it would appear, requiring-- 
excellent programming, most excellent MPI implementation].

By the way, if you've used Intel's mkl, you may have run with hybrid code 
already and not know it [do you know how your system sets OMP_NUM_THREADS 
?].

-Galen
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