I am using OpenMPI 1.8.3 on a linux cluster to run fairly long CFD (computational fluid dynamics) simulations using 16 MPI processes. The calculations last several days and typically involve millions of MPI exchanges. I use the Intel Fortran compiler, and when I compile with the -openmp option and run with only one OpenMP thread per MPI process, I tend to get deadlocks after several days of computing. These deadlocks only occur in about 1 out of 10 calculations, and they only occur after running for several days. I have eliminated things like network glitches, power spikes, etc, as possibilities. The only thing left is the inclusion of the OpenMP option - even though I am running with just one OpenMP thread per MPI process. I have read about the issues with MPI_THREAD_INIT, and I have reduced the REQUIRED level of support to MPI_THREAD_FUNNELED, down from MPI_THREAD_SERIALIZED. The latter was not necessary for my application, and I think the reduction in level of support has helped, but not completely removed, the deadlocking. Of course, there is always the possibility that I have coded my MPI calls improperly, even though the code runs for days on end. Maybe there's that one in a million possibility that rank x gets to a point in the code that is so far ahead of all the other ranks that a deadlock occurs. Placing MPI_BARRIERs has not helped me find any such situation.
So I have two questions. First, has anyone experienced something similar to this where inclusion of OpenMP in an MPI code has caused deadlocks? Second, is it possible that reducing the REQUIRED level of support to MPI_THREAD_SINGLE will cause the code to behave differently than FUNNELED? I have read in another post that SINGLE and FUNNELED are essentially the same thing. I have even noted that I can spawn OpenMP threads even when I use SINGLE. Thanks Kevin McGrattan National Institute of Standards and Technology 100 Bureau Drive, Mail Stop 8664 Gaithersburg, Maryland 20899 301 975 2712
