Wavelength stealing: An opportunistic approach to channel sharing in multi-chip photonic interconnects

Silicon photonic technology offers seamless integration of multiple chips with high bandwidth density and lower energy-per-bit consumption compared to electrical interconnects. The topology of a photonic interconnect impacts both its performance and laser power requirements. The point-to-point (P2P) topology offers arbitration-free connectivity with low energy-per-bit consumption, but suffers from low node-to-node bandwidth. Topologies with channel-sharing improve inter-node bandwidth but incur higher laser power consumption in addition to the performance costs associated with arbitration and contention. In this paper, we analytically demonstrate the limits of channel-sharing under a fixed laser power budget and quantify its maximum benefits with realistic device loss characteristics. Based on this analysis, we propose a novel photonic interconnect architecture that uses opportunistic channel-sharing. The network does not incur any arbitration overheads and guarantees fairness. We evaluate this interconnect architecture using detailed simulation in the context of a 64-node photonically interconnected message passing multichip system. We show that this new approach achieves up to 28% better energy-delay-product (EDP) compared to the P2P network for HPC applications. Furthermore, we show that when applied to a cluster partitioned into multiple virtual machines (VM), this interconnect provides a guaranteed 1.27× higher node-to-node bandwidth regardless of the traffic patterns within each VM.