[pooma-dev] How to run in parallel

[James Crotinger]

Dave asked:
> What is the command line that I should use to run in parallel with
> say 2 processors using either mpi or shmem?

and Jeffrey replied:
> The Pooma source code (src/Utilities/Options.cmpl.cpp:
> Options::usage) seems to indicate that adding `--pooma-threads 5'
> will set a concurrency level of 5.  I do not know how to check
> whether five

Actually, the --pooma-threads option only applies if you're running with
threads.

How one uses MPI is, I believe, system dependent. The file
docs/parallelism.html says to do

  mpirun -np 4 mycode -mpi 

to use MPI, which works on the SGI with the various MPI libraries. 

I can't find any direct documentation for shared memory, but I believe that
you do:

  mycode -shmem -np 4

to run with shared memory.

I think it is unfortunate that we're using "-shmem" here. SHMEM is Cray's
system for making a logical memory space on a set of distributed memory
computers. It provides high-performance one-sided messaging. If we ever get
back to running on Cray's, it would probably be a good idea to put Cheetah
on SHMEM, but I don't think there is a version that does that right now. mm
simply implements shared memory between forked processes. 

Mike thinks that the term "shmem" has been used more generically for
one-sided messaging using shared memory, which is probably why Cheetah chose
it, but a quick web search turned up hits that deal almost exclusively with
Cray's SHMEM, so if we tell folks that POOMA or Cheetah uses shmem it could
be quite misleading. 

(Actually, Burton Smith from Cray was through here the week before last and
mentioned that shmem is being implemented on other vendors' hardware and so
it might be a good thing to explore at some point, but I don't think we want
to go there right now.)

  Jim

BTW, the README was out of date - the tutorials are in docs. I've fixed
this.
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