[Beowulf] emulating MPI?

[John Hearns]

On Mon, 2004-06-28 at 19:22, Robert G. Brown wrote:
> On Mon, 28 Jun 2004, John Wohlbier wrote:
> 
> > Hi,
> > I'm wondering if there is a way to emulate MPI,
> > so that MPI software development may be done on a single
> > processor box and run with "virtual nodes."
> 
> Doesn't MPI let you vary the number of tasks independent of the actual
> host list?  Or do you mean something else?
> 
Indeed it does. Just use a machines file something like:
localhost:n

I agree - that should get you up and running for tests on a single box.
The documentation for mpich says that 'n' is the number of processors.
But you can increase that number.

http://www-unix.mcs.anl.gov/mpi/mpich/docs/mpichman-chp4/node69.htm#Node70

I stupidly just tried to start 100 processes on a dual CPU box
and promptly ran out of semaphores. Ahem.