[mvapich-discuss] MPI_Info to register buffers at allocation time?

[Jeff Hammond]

I recall from looking at MPICH source that neither MPI_Alloc_mem nor
MPI_Win_{create,allocate} do anything about memory registration.  Does
MVAPICH do anything different in this respect or does it do IB registration
on-the-fly for all communication (and presumably maintain a cache for
future reuse)?  Is it possible to set an MPI_Info key that instructs the
implementation to do IB registration immediately during these calls?

My motivation is that I do a lot of RMA and I'd like to not see a latency
hit the first time I communicate between processes.  Additionally, I see
that MVAPICH-X SHMEM latency is much better than MPI-RMA latency, which
does not make sense to me (there is no semantic reason for this as of
MPI-3, but I recognize implementations do not necessarily reflect all that
is possible in the specification) and I can only assume that some fraction
of this improvement comes from the pre-registration of the SHMEM symmetric
heap.

If this features are not implemented, please consider this inquiry a
feature request for future releases :-)

Thanks,

Jeff

-- 
Jeff Hammond
jeff.science at gmail.com
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