[mvapich-discuss] MPI and posix shared memory.

[Devendar Bureddy]

Hi Ben

Since you are using your own shared-memory design, we are not sure what
could be happening here. Could you please send us a reproducer? Also, can
you try adding a barrier between broadcasts and see whether you see any
different behavior

-Devendar



On Fri, Aug 30, 2013 at 3:02 PM, Ben <Benjamin.M.Auer at nasa.gov> wrote:

> We have a code that makes use of posix shared memory on each node to help
> with the memory footprint. As part of the larger shared memory package in
> the code we have been trying to add a set of node broadcast routines that
> broadcast a piece of data in shared memory on one node to the shared memory
> in the other nodes. This code has not been working and we have traced it to
> the actual call to MPI_BCast. We also tried just doing sends and recieves
> with no luck as well. It seems as though the first time the broadcast is
> called the routine functions properly but on subsequent calls it fails. The
> mpi_status itself returns without error but the results of the broadcast
> are just plain wrong.
>
> If before calling the MPI_Bcast we allocate a local, non-shared memory
> variable of the same size of the data to be broadcast on each process in
> the communicator, copy from the shared memory to the local memory. Then
> MPI_Bcast with the local copy and finally copy the from the local back to
> the shared memory the routine functions properly. It seems as though the
> broadcast itself just does not function properly when then data is posix
> shared memory.  I tried setting MV2_USE_SHARED_MEM=0 to turn off the shared
> memory routines in mvapich itself which did not fix the bcasts.
>
> Are there just issues with trying to do mpi communications with shared
> memory data? Is it possible this is a bug? We are using mvapich 1.9. If
> this is a possible bug I can try to come up with a reproducer.
>
> --
> Ben Auer, PhD   SSAI, Scientific Programmer/Analyst
> NASA GSFC,  Global Modeling and Assimilation Office
> Code 610.1, 8800 Greenbelt Rd, Greenbelt, MD  20771
> Phone: 301-286-9176               Fax: 301-614-6246
>
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>



-- 
Devendar
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