Communication-Aware Hardware-Assisted MPI Overlap Engine

Abstract

Overlap of computation and communication is critical for good application-level performance. Modern high-performance networks offer Hardware-assisted tag matching and rendezvous offload to enable communication progress without involving the host CPU. However, hardware based offload cannot be used in many situations due to various hardware limitations and performance issues. Furthermore, hardware-based designs cannot provide good overlap for common communication patterns involving unexpected messages or non-contiguous datatypes. In this paper, we address these limitations by designing a communication-aware overlap engine for MPI that uses novel hardware-assisted and softwarebased solutions to extract overlap for both expected and unexpected messages. The proposed design adapts to the application's communication requirements including message size, datatype, and relative timing of processes using heuristics and history-driven predictions. We evaluate the proposed designs against state-of-the-art MPI libraries and show up to 41% and 22% reduction in latency for collective operations and stencil-based application kernels on 1024 and 128 nodes, respectively, as well as 23% improvement in communication performance of the P3DFFT application.