parallelizing OpenMP apps

[Craig Tierney]

On Thu, Mar 22, 2001 at 11:11:08AM -0800, Mattson, Timothy G wrote:
> 
> Mapping OpenMP onto an HPF-style programming environment can be as-hard or
> harder than going straight to MPI.  Before taking such a drastic step, you
> should consider your options in the OpenMP space.  
> 
> I haven't personnally used it, but the OMNI compiler project at RWCP lets
> you run OpenMP programs on a cluster.  I can't find their URL right now (my
> web proxy is acting up), but I think you can learn more about it by
> following links off the OpenMP web sige (www.openmp.org).  KAI also has a
> system that supports moving OpenMP onto clusters --- though I don't think
> its an official product yet (you'll have to ask them).
>

RWCP's OMNI compiler is an OpenMP preprocessor. It allows you to
run OpenMP codes on an SMP system as if you really had an OpenMP 
compiler.  It does not work with clusters, unless you have a cluster
of SMP boxes, and you use a combination of OpenMP and MPI.

I have been testing the latest version of OMNI on a couple of
ES40s (2 cpus and 4 cpus).  The have some test OpenMP codes that do
compile cleanly.  I am getting pretty good speed ups with the codes.
I am seeing a 3.2-3.4x for 4 cpus, depending on the test code (NAS
Parallel Benchmarks).  With the memory bandwidth of an ES40, I don't
think I would get much better than that.

It works with C and Fortran 77.  It does not work with Fortran 90.
I would like to try and get MM5 or some other real codes going.
My initial attempt to compile MM5 with OpenMP failed, but right
now I claim pilot error.

Craig
 
> Good luck.
> 
> --Tim
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Greg Lindahl [mailto:lindahl at conservativecomputer.com]
> Sent: Thursday, March 22, 2001 9:57 AM
> To: beowulf at beowulf.org
> Subject: parallelizing OpenMP apps
> 
> 
> On Thu, Mar 22, 2001 at 12:05:21PM +0100, Ole W. Saastad wrote:
> 
> > Many of my colleges run climate models with OpenMP on fast
> > sequential machines and would consider MPI based clusters if
> > they could get some help to make the transition.
> 
> I would suggest checking out SMS:
> 
> http://www-ad.fsl.noaa.gov/ac/sms.html
> 
> It is a system aimed at the weather community. You add HPF-like
> directives, and the system does the rest. We have seen O(100) speedup
> on O(100) nodes... for a real code used for production air travel
> weather prediction in the US.
> 
> It only does some kinds of stencils and some kinds of spectral codes,
> and it only does F77, but if it does what your code uses...
> 
> -- greg
> 
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-- 
Craig Tierney (ctierney at hpti.com)
phone: 303-497-3112