[Beowulf] More cores/More processors/More nodes?

[Peter Wainwright]

Please enlighten a baffled newbie:

Now there are motherboards with 8 sockets; quad-core processors; and
clusters
with as many nodes as you can shake a stick at.
It seems there are at least 3 dimensions for expansion.  What (in your
opinion) is the right tradeoff between more cores, more processors and
more
individual compute nodes?

In particular, I am thinking of in-house parallel finite difference /
finite element codes,
parallel BLAS, and maybe some commercial Monte-Carlo codes (the last
being an
embarrassingly parallel problem).

I have been set the task of building our first cluster for these
applications.
Our existing in-house codes run on an SGI machine with a parallelizing
compiler.
They would need to be ported to use MPI on a cluster.  However, I do not
understand
what happens when you have multi-processor/multi-core nodes in a
cluster.  Do you
just use MPI (with each thread using its own non-shared memory) or is
there any
way to do "mixed-mode" programming which takes advantage of shared
memory within a
node (like, an MPI/OpenMP hybrid?).

Peter Wainwright




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