Collective Communication on FPGA Clusters with Static Scheduling.

FPGA-centric clouds and clusters provide direct and programmable interconnects with obvious benefits for communication latency and bandwidth. One rarely studied aspect of DPI is that they facilitate application-aware routing: if communication patterns are static and known a priori, as is usually the case, then judicious routing can reduce congestion, latency, and the hardware required. In this study we explore applying the method of offline/static routing to collective operations, in particular, multicast and reduction. An entirely new communication infrastructure is proposed and implemented, including switch design and routing algorithm. A substantial improvement in performance is obtained, especially for multicast. We believe that this is one of the few general offline/static routing solutions for real HPC clusters, and FPGA-centric clusters in particular.