_______________________________________________Hi all, this is the first time I post to the list (although I have read it for a while now). I hope this helps.
I'm heavily using MPI_THREAD_MULTIPLE on multicores (sm BTL) and my programs work fine from a CORRECTNESS point of view. I use OpenMPI 1.6 (SVN rev. 26429) and pthreads on Linux.
This said, the performance is still very poor. Some of my programs become a thousand times slower. After some profiling/tracing, I found out that the Linux scheduler gave CPU time to threads stuck in blocking calls (Ssend, Recv, Wait, etcetera). It seems to me that the MPI implementation can be improved to avoid spending CPU time in threads waiting for messages.
In short, my experience is that the implementation is correct but not very efficient so far.
I have a few questions:
1. My OpenMPI version is more than a year old. Have these performance issues been fixed in the latest versions?
2. If not, perhaps I could contribute to OpenMPI multithreading support. Who takes care of this? How can I help?
-- Pablo Barrio Dpt. Electrical Engineering - Technical University of Madrid Office C-203 Avda. Complutense s/n, 28040 Madrid Tel. (+34) 915495700 ext. 4234 @: email@example.com
On 19/12/13 01:49, Ralph Castain wrote:
This was, in fact, a primary point of discussion at last week's OMPI developer's conference. Bottom line is that we are only a little further along than we used to be, but are focusing on improving it. You'll find good thread support for some transports (some of the MTLs and at least the TCP BTL), not so good for others (e.g., openib is flat-out not thread safe).
On Dec 18, 2013, at 3:57 PM, Blosch, Edwin L <firstname.lastname@example.org> wrote:
_______________________________________________I was wondering if the FAQ entry below is considered current opinion or perhaps a little stale. Is multi-threading still considered to be ‘lightly tested’? Are there known open bugs?
7. Is Open MPI thread safe?
Support for MPI_THREAD_MULTIPLE (i.e., multiple threads executing within the MPI library) and asynchronous message passing progress (i.e., continuing message passing operations even while no user threads are in the MPI library) has been designed into Open MPI from its first planning meetings.
Support for MPI_THREAD_MULTIPLE is included in the first version of Open MPI, but it is only lightly tested and likely still has some bugs. Support for asynchronous progress is included in the TCP point-to-point device, but it, too, has only had light testing and likely still has bugs.
Completing the testing for full support of MPI_THREAD_MULTIPLE and asynchronous progress is planned in the near future.
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