[Mpi3-hybridpm] Endpoints Proposal

[Sur, Sayantan]

> > Just as an example: Suppose there is an MPI+OpenMP app that runs on 16
> cores with 1 MPI rank and 16 threads. On certain platform you find out if
> there are two endpoints you get better network utilization. In this case, can
> you not just run 2 MPI ranks with 8 threads each? How is this not achieve the
> same effect as your endpoint proposal?
> 
> Most apps run best with MPI only until they run out of memory.  

Yes, and folks that run out of memory (MPI only) would use threading to reduce some of the memory consumption.

Adding endpoints that behave like ranks would not help the memory case.

> Your
> argument can and often does lead back to MPI-only if applied inductively.

Folks can always adjust the balance of MPI ranks-to-threads to get to a point where adding more processes does not increase network-related performance and achieves the memory balance that you mention above.

> It's really not an intellectually stimulating example to discuss.
>

I am happy to look at other concrete examples that show the benefit of endpoints.

Sayantan.

 
> Jeff
> 
> --
> Jeff Hammond
> Argonne Leadership Computing Facility
> University of Chicago Computation Institute jhammond at alcf.anl.gov / (630)
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