Everything that Brian said, plus: note that the MCA param that Christoph mentioned is specifically for the "sm" (shared memory) transport. Each transport has their own set of MCA params (e.g., mca_btl_tcp_eager_limit, and friends).
On Dec 16, 2013, at 3:19 PM, "Barrett, Brian W" <bwba...@sandia.gov> wrote: > Siddhartha - > > Christoph mentioned how to change the cross-over for shared memory, but it's > really per-transport (so you'd have to change it for your off-node transport > as well). That's all in the FAQ you mentioned, so hopefully you can take it > from there. Note that, in general, moving the eager limits has some > unintended side effects. For example, it can cause more / less copies. It > can also greatly increase memory usage. > > Good luck, > > Brian > > On 12/16/13 1:49 AM, "Siddhartha Jana" <siddharthajan...@gmail.com> wrote: > >> Thanks Christoph. >> I should have looked into the FAQ section on MCA params setting @ : >> http://www.open-mpi.org/faq/?category=tuning#available-mca-params >> >> Thanks again, >> -- Siddhartha >> >> >> On 16 December 2013 02:41, Christoph Niethammer <nietham...@hlrs.de> wrote: >>> Hi Siddhartha, >>> >>> MPI_Send/Recv in Open MPI implements both protocols and chooses based on >>> the message size which one to use. >>> You can use the mca parameter "btl_sm_eager_limit" to modify the behaviour. >>> >>> Here the corresponding info obtained from the ompi_info tool: >>> >>> "btl_sm_eager_limit" (current value: <4096>, data source: default value) >>> Maximum size (in bytes) of "short" messages (must be >= 1) >>> >>> Regards >>> Christoph Niethammer >>> >>> -- >>> >>> Christoph Niethammer >>> High Performance Computing Center Stuttgart (HLRS) >>> Nobelstrasse 19 >>> 70569 Stuttgart >>> >>> Tel: ++49(0)711-685-87203 >>> email: nietham...@hlrs.de >>> http://www.hlrs.de/people/niethammer >>> >>> >>> >>> ----- Ursprüngliche Mail ----- >>> Von: "Siddhartha Jana" <siddharthajan...@gmail.com> >>> An: "OpenMPI users mailing list" <us...@open-mpi.org> >>> Gesendet: Samstag, 14. Dezember 2013 13:44:12 >>> Betreff: [OMPI users] Configuration for rendezvous and eager protocols: >>> two-sided comm >>> >>> >>> >>> Hi >>> >>> >>> In OpenMPI, are MPI_Send, MPI_Recv (and friends) implemented using >>> rendezvous protocol or eager protocol? >>> >>> >>> If both, is there a way to choose one or the other during runtime or while >>> building the library? >>> >>> >>> If there is a threshold of the message size that dictates the protocol to >>> be used, is there a way I can alter that threshold value? >>> >>> >>> If different protocols were used for different versions of the library in >>> the past, could someone please direct me to the exact version numbers of >>> the implementations that used one or the other protocol? >>> >>> >>> Thanks a lot, >>> Siddhartha >>> _______________________________________________ >>> users mailing list >>> us...@open-mpi.org >>> http://www.open-mpi.org/mailman/listinfo.cgi/users >>> _______________________________________________ >>> users mailing list >>> us...@open-mpi.org >>> http://www.open-mpi.org/mailman/listinfo.cgi/users >> > > > -- > Brian W. Barrett > Scalable System Software Group > Sandia National Laboratories > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
