[petsc-users] MPI v. Pthreads ?

[Jed Brown]

On Sun, Jul 10, 2011 at 13:15, John Chludzinski <jchludzinski at gmail.com>wrote:

> "If you don't have a real MPI installed"?
>
> I installed (on Cygwin) using: ./configure CC=gcc FC=gfortran
> --download-mpich=1 PETSC_ARCH=arch-cygwin-gnu
>
> I've compiled some example MPI code using mpicc. And I've run the generated
> executable with: mpiexec -n <some int> <executable>.
>
> "ps" says it created n-number of processes.
>
> But it is on a 2-proc/4-core Windows box running Cygwin (of course, not
> configured as a cluster).
>
> Do I have "real MPI" installed?
>

Yes.

Note that threading offers very little potential performance improvement on
a system like this. It becomes more important if you have many "fat" nodes,
for example if each node has 4 sockets with 12 cores per socket and you want
to "strong scale" such that the subdomains become very small (less than 10k
unknowns if inexpensive preconditioners are working, also depending on the
network and intra-node bandwidth).
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