An Efficient Collaborative Communication Mechanism for MPI Neighborhood Collectives

Neighborhood collectives are introduced in MPI3.0 standard to provide users with the opportunitv to define their own communication patterns through the process topologv interface of MPI. In this paper, we propose a collaborative communication mechanism based on common neighborhoods that might exist among groups of k processes. Such common neighborhoods are used to decrease the number of communication stages through message combining. We show how designing our desired communication pattern can be modeled as a maximum weighted matching problem in distributed hvpergraphs, and propose a distributed algorithm to solve it. Moreover, we consider two design alternatives: topologvagnostic and topologv-aware. The former ignores the phvsical topologv o7 the svstem and the mapping o7 processes, whereas the latter takes them into account to further optimize the communication pattern. Our experimental results show that we can gain up to 8x and 5.2x improvement for various process topologies and a SpMM kernel, respectivelv.