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MPI on one multicore CPU

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Old   August 21, 2008, 23:49
Default Hello, I am so new to OpenF
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Wayne Miller
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Hello,

I am so new to OpenFOAM that I have not even installed it yet, but I have a few questions about how to run parallel on a single multi-core CPU. I plan to build a modest CFD desktop computer with a single Intel Q9550 CPU (12MB L2 cache) and 16GB RAM running 64-bit Ubuntu Linux 8.04. I've seen a few postings about benchmarks on various combinations of one or more multi-core CPUs but I don't know what it took to make that happen.

Does the basic OpenFOAM MPI implementation know how to use a single multi-core CPU as multiple independent processors? For example will a quad core CPU be used to run 4 independent parallel processes?

Are any special command line directives or compiler options needed to use a single multi-core CPU in this way?

What MPI distribution is recommended for this (LAM, OpenMPI, MPICH(1,2),...)

Thank you,
Wayne Miller
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Old   August 22, 2008, 01:15
Default Hi Wayne, a multi-core CPU is
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Francesco Del Citto
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Hi Wayne,
a multi-core CPU is seen in exactly the same way of multiple CPUs.
OpenFOAM can use any mpi implementation, by only recompiling Pstream library. The standard setting, however, uses OpenMPI.

If you want to test your multi-core CPU, just take a tutorial, decompose it with decomposePar and run "mpirun -n <processors> <your_solver> -parallel"

Francesco
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Old   August 22, 2008, 17:03
Default Thank you, that sounds nice an
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Wayne Miller
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Thank you, that sounds nice and simple.

Wayne
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Old   December 19, 2009, 12:40
Default 4 CPUs vs. 1 CPU
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Hi Francesco,

My configuration is exactly the same as above and aslo I have 2560,000 cells.

Unfortunately, running with 4 CPUs on a quad core (with mpirun) nearly needs the same amount of time as that of 1 cpu.

Do you know where the problem is?

Thanks in advance
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Old   January 6, 2010, 00:31
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Mahendra
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hi fra76

As you have mentioned that OpenFOAM can use any mpi, by recompiling the Pstream library. Now I want to use intel's mpi, can u please let me know what modifications do i need to do in the Pstream library so that I can use either OpenMPI or Intel's mpi.

Thanks and Regards,
Mahendra.
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Old   January 7, 2010, 08:53
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Mahendra
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hi,

Ok I got a starting Point from this link

OF15x with MPICH2

I will try it.

Regards,
Mahendra
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