On the routing and scalability of MZI-based optical Benes interconnects

Silicon Photonic interconnects are a promising technology for scaling computing systems into the exascale domain. However, there exist significant challenges in terms of optical losses and complexity. In this work, we evaluate the applicability of a thermally/electrically tuned Beneg network based on Mach-Zehnder Interferometers for on-chip and inter-chip interconnects as regards its scalability. We examine how insertion loss, laser power and switching energy consumption scale with the number of endpoints. In addition, we propose a set of hardware-inspired routing strategies that leverage the inherent asymmetry present in the switching components. We evaluate a range of network sizes, from 16 up to 256 endpoints, using 8 realistic and synthetic workloads and found very promising results. Our routing strategies offer a reduction in path-dependent insertion loss of up to 35% in the best case, as well as a laser power reduction of 31% for 32 endpoints. In addition, bit-switching energy is reduced by between 8% and 15% using the most efficient routing strategy, depending on the communication workload. We also show that workload execution time can be reduced with the best strategies by 5%-25% in some workloads, while the worst-case increases are at most 3%. Using our routing strategies, we show that under the examined technology parameters, a 32-endpoint interconnect can be considered for the NoC domain in terms of insertion loss and laser power, even when using conservative parameters for the modulator. (C) 2020 Elsevier B.V. All rights reserved.