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Subject: Re: [OMPI users] Thread as MPI process
From: Mikael Lavoie (mikael.lavoie_at_[hidden])
Date: 2010-09-21 04:54:16


Sorry, but i get lost in what i wanna do, i have build a small home cluster
with Pelican_HPC, that user openMPI, and i was trying to find a way to get a
multithreaded program work in a multiprocess way without taking the time to
learn MPI. And my vision was a sort of wrapper that take C posix app src
code, and convert it from pthread to a multiprocessMPI app. But the problem
is the remote memory access, that will only be implemented in MPI 3.0(for
what i've read of it).

So, after 12 hour of intensive reading about MPI and POSIX, the best way to
deal with my problem(running a C pthreaded app in my cluster) is to convert
the src in a SPMD way.
I didn't mentionned that basicly, my prog open huge text file, take each
string and process it through lot's of cryptographic iteration and then save
the result in an output.out like file.
So i will need to make the master process split the input file and then send
them as input for the worker process.

But if you or someone else know a kind of interpretor like program to run a
multithreaded C program and convert it logically to a master/worker
multiprocess MPI that will be sended by ssh to the interpreter on the worker
side and then lunched.

This is what i've tried to explain in the last msg. A dream for the hobyist
that want to get the full power of a night-time cluster, without having to
learn all the MPI syntax and structure.

If it doesn't exist, this would be a really great tool i think.

Thank you for your reply, but i think i have answered my question alone...
No Pain, No Gain...

> On 20 Sep 2010, at 22:24, Mikael Lavoie wrote:
> > I wanna know if it exist a implementation that permit to run a single
> host process on the master of the cluster, that will then spawn 1 process
> per -np X defined thread at the host specified in the host list. The host
> will then act as a syncronized sender/collecter of the work done.
> I don't fully understand you explanation either but I may be able to help
> clear up what you are asking for:
> If you mean "pthreads" or "linux threads" then no, you cannot have
> different threads on different nodes under any programming paradigm.
> However if you mean "execution threads" or in MPI parlance "ranks" then
> yes, under OpenMPI each "rank" will be a separate process on one of the
> nodes in the host list, as Jody says look at MPI_Comm_Spawn for this.
> Ashley,
> --
> Ashley Pittman, Bath, UK.
> Padb - A parallel job inspection tool for cluster computing
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