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Dear MPi users,
I'm using IntelMPI cs-2011. My code (OpenMP + MPI) does for each time step some send and receive MPI calls after a kernel computation. MPI calls are used for ghost cell exchange. (few kbytes)
I've noted a significative slowdown during the computation. I suppose the problem is in some low level MPI setting because by using OpenMPI that problem disappear. I'm using Inifiniband and 12 cores on 1 node, so just intranode communication is used.
I disabled shared memory inside a node, used dapl for intranode, decreased I_MPI_INTRANODE_THRESHOLD, set I_MPI_DAPL_TRANSLATION_CACHE to 0, without any good improvement.
Do you have an idea because the p2p calls slowdown in running?
Thanks a lot.
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Hey unrue,
Thanks for posting. Unfortunately, performance issues are notoriously hard to track down. Based on your original post, can I assume you're mostly using p2p messages in your application?
The first thing I would suggest is grabbing the latest Intel® MPI Library and giving that a try. We have Intel MPI Library 4.1 Update 1 that was released not too long ago. The beauty of it is you can install the new runtimes and re-run your application without having to recompile (Intel MPI 4.0 - which is probably what you have - is binary compatible with Intel MPI 4.1 - the latest).
You can grab the latest package from the Intel® Registration Center - just login using your e-mail address and the password you created when you originally downloaded the library.
Ideally, we'd like to have a reproducer that we can test out locally. If that's not possible, can you provide some debug output (I_MPI_DEBUG=5) when running your application, as well as the full set of env variables you're setting? What's the nature of the performance slowdown between Intel MPI and OpenMPI - 10% or 90% slowdown?
Looking forward to hearing back soon.
Regards,
~Gergana
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Gergana Slavova (Intel) wrote:
The first thing I would suggest is grabbing the latest Intel® MPI Library and giving that a try. We have Intel MPI Library 4.1 Update 1 that was released not too long ago. The beauty of it is you can install the new runtimes and re-run your application without having to recompile (Intel MPI 4.0 - which is probably what you have - is binary compatible with Intel MPI 4.1 - the latest).
Regards,
~Gergana
Dear Georgana,
I tried latest IntelMPi version as you suggested, but the problem still remain .. :(

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