Cartesian Collective Communication
Jesper Larsson Träff, Sascha Hunold · 2019
We introduce Cartesian Collective Communication as sparse, collective communication defined on processes (processors) organized into d-dimensional tori or meshes. Processes specify local neighborhoods, e.g., stencil patterns, by lists of relative Cartesian coordinate offsets. The Cartesian collective operations perform data exchanges (and reductions) over the set of all neighborhoods such that each process communicates with the processes in its local neighborhood. The key requirement is that local neighborhoods must be structurally identical (isomorphic). This makes it possible for processes to compute correct, deadlock-free, efficient communication schedules for the collective operations locally without any interaction with other processes. Cartesian Collective Communication substantially extends collective neighborhood communication on Cartesian communicators as defined by the MPI standard, and is a restricted form of neighborhood collective communication on general, distributed graph topologies.