Arch Linux

My understanding is that the use of MPI_THREAD_MULTIPLE is officially unsupported by upstream and disabled by default.

See http://comments.gmane.org/gmane.comp.clustering.open-mpi.user/13660

I've seen similar discussions elsewhere. I think they mean that the thread level called THREAD_MULTIPLE is unsafe. The MPI specification defines four thread levels: THREAD_{SINGLE, FUNNELED, SERIALIZED, MULTIPLE}. Only in THREAD_MULTIPLE are different threads allowed to make simultaneous MPI calls. Yet if I understand correctly, to use *any* of these modes openmpi must be configured with --enable-mpi-thread-multiple.

Would it be possible for you to verify (doc or asking upstream) please ? If it is safe and there is no performance impact, then I will enable it with pleasure.

I've started a thread on the mailing list.

http://www.open-mpi.org/community/lists/users/2012/10/20421.php

So far I've confirmed that you have to configure with --enable-thread-multiple even to use THREAD_FUNNELED and THREAD_SERIALIZED.

I've also inquired if there will be any impact on users who don't need thread support.

Any news about impact ?

Yes, here is the thread.

http://www.open-mpi.org/community/lists/users/2012/10/20579.php

They say, "Short answer: yes, enabling threading impacts performance."

Thanks for checking with them. As it will impact performance, I will not enable threading in the package.