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Subject: Re: [OMPI users] Basic Question about MPI
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-05-26 09:53:14


Keep in mind the difference between the MPI standard and
implementations of that standard. To be specific: Open MPI is one
implementation of the MPI standard (see www.mpi-forum.org for the
standard document, v2.1 is the latest version of that doc).

Open MPI generally depends on finding your executable on the node
where it is running. This usually means specifying an absolute
filename than can be exec'ed directly or a relative filename that can
be found either with relation to the cwd or in the PATH.

How this executable gets to the node to execute is a different
question. The executable may be located in a local filesystem or a
networked filesystem (e.g., NFS). Many cluster-based users of MPI
with small-ish systems (~32-64 nodes) use an NFS server to make their
executables visible on all nodes without the bother of manually
copying executables between nodes.

That being said, there are many scheduling/resource managing systems
out there that will pre-stage executables (and other data files) to
desired nodes before MPI tries to run them. These are beyond (Open)
MPI's scope -- from OMPI's perspective, we just find the executable in
the PATH; it doesn't really matter to OMPI how it got there.

On May 26, 2009, at 2:11 AM, Charles Salvia wrote:

> I am very new to the concept of MPI, and have only recently begun
> researching it. I have a very basic question about the way MPI works.
>
> How exactly does MPI distribute user-created applications (binary
> code) over a network? Does it actually copy the binary into the
> local memory of each node, and execute it? If so, doesn't this put
> serious restrictions on the heterogeneity of the network? For
> example, in order to run a distributed application (compiled with
> gcc) over a typical Linux cluster, you'd need to make sure that each
> node has the same version of glibc, or there could be issues running
> the binary.
>
> Any information would be greatly appreciated.
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users

-- 
Jeff Squyres
Cisco Systems