FlexiShare: Channel sharing for an energy-efficient nanophotonic crossbar

On-chip network is becoming critical to the scalability of future many-core architectures. Recently, nanophotonics has been proposed for on-chip networks because of its low latency and high bandwidth. However, nanophotonics has relatively high static power consumption, which can lead to inefficient architectures. In this work, we propose FlexiShare - a nanophotonic crossbar architecture that minimizes static power consumption by fully sharing a reduced number of channels across the network. To enable efficient global sharing, we decouple the allocation of the channels and the buffers, and introduce novel photonic token-stream mechanism for channel arbitration and credit distribution The flexibility of FlexiShare introduces additional router complexity and electrical power consumption. However, with the reduced number of optical channels, the overall power consumption is reduced without loss in performance. Our evaluation shows that the proposed token-stream arbitration applied to a conventional crossbar design improves network throughput by 5.5× under permutation traffic. In addition, FlexiShare achieves similar performance as a token-stream arbitrated conventional crossbar using only half the amount of channels under balanced, distributed traffic. With the extracted trace traffic from MineBench and SPLASH-2, FlexiShare can further reduce the amount of channels by up to 87.5%, while still providing better performance - resulting in up to 72% reduction in power consumption compared to the best alternative.