Talk by Jesper Larsson Träff on December 3rd

Cartesian Collective Communication “Advice to users”, “Advice to implementers”, and “Advice to Standardizers”

Cartesian Collective Communication (or stencil communication) is a restricted form of general, sparse, graph neighborhood collective communication as known in for instance MPI. The prime charactistic of Cartesian Collective Communication is that processes organized in a d-dimensional torus (or mesh) all communicate with the same, relative set of neighbors. In the talk, we discuss how Cartesian Collective Communication can be incorporated and used in MPI, giving both “advice to users”, “advice to implementers”, and “advice to standardizers”. We also present new, message-combining algorithms for efficiently supporting Cartesian Collective alltoall and allgather Communication (for small problems), and give of experimental results showing that this form of sparse collective communication can be supported with a performance advantage.