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Author Topic: OpenMP Threads and Threads MPI  (Read 591 times)

Dapke36

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OpenMP Threads and Threads MPI
« on: March 10, 2020, 08:20:13 am »

I'm still trying to wrap my brain around when to use OpenMP and when to use OpenMP Threads MPI (~"MPI) in FDS/Pyrosim.  I read the FDS users guide section 3.3.1, but still struggling on application...and i'm hoping someone can help!

The current machine I am utilizing for smaller runs is 12 GB ram with a Xeon e5 with 4 physical cores reported in that 1 cpu. When I read the user's guide, I am getting confused when they are talking about mapping to cores.

Using that hardware above, lets say I have a model with 4 meshes.  Should I be doing an MPI thread per core, i.e.:

Open MP Threads: 1
Open MP Threads MPI: 4
Open MP Stack: 200M


Or should I be doing 1 mpi thread per physical CPU and 1 OpenMP thread per core of that cpu? i.e.:

Open MP Threads: 4
Open MP Threads MPI: 1
Open MP Stack: 200M


Is MPI supposed to be per core available (parallel or cluster, whatever's linked), or per CPU? 

If there's one MPI per core, I should try to get my # of meshes to match the # of cores available, right? (with exceptions for dense meshes and distribution, understandably) Or is the OpenMP Thread supposed to match the # of cores?


If I double the CPU's on the machine to 2 physical CPU's, each with 4 cores (8 cores total), would it then be 8 MPI processes?

Any insight that can be offered is appreciated!
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chang

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Re: OpenMP Threads and Threads MPI
« Reply #1 on: September 08, 2020, 04:56:14 pm »

Did you ever figur this out? Very curious myself.
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JoanneFraser

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Re: OpenMP Threads and Threads MPI
« Reply #2 on: October 21, 2020, 05:52:18 pm »

I would like to know too. It sounds very complicate and for me it is very hard to understand what you write there because I am a beginner. My dream is to become a web developer and to start working for https://www.brainvire.com/php-website-development-services/, but now I have poor knowledge at this so it is so exhausting. Now, after practicing, I like to search on the forums for different problems that other people face. If I know how to solve them I write to them. If I don't know I am just waiting for someone to respond.
« Last Edit: October 24, 2020, 06:06:09 am by JoanneFraser »
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