[mpiwg-rma] [EXTERNAL] Re: MPI_WIN_CREATE for intercommunicators

Barrett, Brian W bwbarre at sandia.gov
Wed Jan 22 11:53:38 CST 2014

On 1/22/14 3:41 AM, "Thomas Jahns" <jahns at dkrz.de> wrote:

>Hello Maik,
>On 01/22/14 10:14, maik peterson wrote:
>> thomas, today you should start thinking about other possibilities
>> to solve your problem. this mpi rma stuff is crappy.
>I guess that very much depends on your kind of machine. We've found it to
>very nice with MVAPICH, not so great with PE and OpenMPI.

Another way to put it; it really depends on how much work your MPI
implementor has put into one-sided for your hardware.  MVAPICH has put in
a good deal of effort to use IB-natvie RDMA semantics when implementing
MPI one-sided.  Open MPI has not put that effort into IB (it has for
another network, but that's a different story), so the performance is much
lower.  Open MPI's largely driven by squeaky wheels, and that wheel's been
pretty quiet :)..


  Brian W. Barrett
  Scalable System Software Group
  Sandia National Laboratories

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