PVM or MPI essential to run parallel applications on aBeowulf?

[Jason Abate]

> >The simplest, but not necessarily most optimal, way to handle this is to
> >treat a dual processor node as if it were 2 nodes. No special
> >programming is required and the benefits are available immediately.
> 
> Thanks, I did try that [2 MPI processes on same system]. Since the 
> OS shifts a lot of work to second processor when the first is pegged, 
> bringing in a second MPI process is not so great [I don't expect it 
> to be].

If you're using MPICH, you can make use of both shared-memory for 
passing messages between processes on a machine, and ethernet for 
messages to remote machines if you configure and 
compile with -comm=shared.   Note that you need to setup a procgroup 
file, not just list each dual-processor machine twice.  It took me a 
while to discover this, but it is crucial for good performance.  
Without specifying the procgroup, using both processors on a node was 
actually _slower_ than only using a single processor - not a good 
thing.

If you need more details on how to setup the procgroup file, check 
the MPICH docs or email me.

-jason


====================================================================
   Jason Abate abate@ticam.utexas.edu www.ticam.utexas.edu/~abate
     Texas Institute for Computational and Applied Mathematics
     304 SHC, University of Texas at Austin,  Austin, TX 78712
     Work: 512-471-6947  Home: 512-912-1012  Fax: 512-471-8694