[mvapich-discuss] 64-bit sized messages?

[Devendar Bureddy]

Hi Chavarría

On Fri, Jun 28, 2013 at 7:41 PM, Chavarria, Daniel G <
daniel.chavarria at pnnl.gov> wrote:

> Hi MVAPICH developers,
>
> I have a problem where I would like to send and receive messages of
> MPI_BYTE type where each message is more than 2GB in size.
>
> This is for a big data type problem where I'm initializing the in-memory
> data containers.  Our local machine here has 64GB per node so 2GB is only a
> fairly small fraction of the node memory, particularly in the context of a
> multithreaded run with a single process per node.
>
> Consulting with our local MPI experts they have suggested to send the
> message in multiple chunks or to use a derived datatype where each element
> is "large".  I'll likely take one of these routes, however it would be nice
> to have an interface where I could execute a MPI_Irecv(void *buf, int64_t
> count, …)
>

This issue was discussed in MPI-3 proposal meetings. For
backward compatibility  the exact above interface is not introduced. In the
new MPI-3 standard, introduced a new datatype called MPI_Count
to properly support large messages (> 2^31)  using nested datatypes. I
would recommend following links for more details on this

http://svn.mpi-forum.org/trac/mpi-forum-web/ticket/265
http://blogs.cisco.com/performance/new-things-in-mpi-3-mpi_count/

The latest release of MVAPICH2 has MPI_Count support. But, there are some
know issues here and this will be stabilized in the future releases.

-Devendar



>
> Is this something that you guys have thought about?  Does it come up in
> the community?
>
> Thanks in advance for your time and attention.
>
> Greetings,
>
> ____________________________
>
> Daniel G. Chavarría
> Research Scientist
> HIGH PERFORMANCE COMPUTING
>
> Pacific Northwest National Laboratory
> 902 Battelle Boulevard
> P.O. Box 999, MSIN: J4-30
> Richland, WA 99352 USA
> Tel.: (509)372-6964
> Cel.: (509)392-9194
> Fax: (509)375-4595
> daniel.chavarria at pnnl.gov
> <applewebdata://2EBC18AC-C046-4FAF-954A-01ED68CF1E45/
> daniel.chavarria at pnnl.gov>
> www.pnnl.gov
>
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-- 
Devendar
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