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Re: [mpi-21] Proposal: Topological Collectives for MPI-3

If I correctly understand your proposal these two functions are just a less powerful version of the MPI_Alltoallv and MPI_Alltoallw. There is nothing in the proposed neighbors collectives that cannot be achieved by using only ONE carefully crafted alltoall[v|w]. Additionally, I hardly see any optimization in terms of communications that can be applied to these neighbors collective and that cannot be applied to the corresponding alltoall collective.

The topology associated with the communicator can be used to determine where data will be sent and from where data will be received inside a small wrapper around the alltoall functions. The two proposed neighbors collective are a perfect example on what kind of functionality a library developed on top of MPI can offer in a very portable manner across all MPI implementations (with a minimal overhead).

  george.

On Jan 11, 2008, at 4:41 PM, Torsten Hoefler wrote:

This proposal introduces new collective operations that operate on
communicators with process topologies. These topological collectives
express common communication patterns for applications that use process
topologies, such as nearest-neighbor data exchange and shifted Cartesian
data exchange. These collectives are usually implemented by the
application programmer. However, a performant implementation of those
operations is not trivial and programmers frequently face problems with
deadlocks.

The full proposal, intended for MPI-3, is attached to this email.
Comments are always welcome!

Best,
 Torsten

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<topo_colls.pdf>

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