PROWAVES: Proactive Runtime Wavelength Selection for Energy-Efficient Photonic NoCs

2.5-D manycore systems running parallel applications are severely bottlenecked by network-on-chip (NoC) latencies and bandwidth. Traditionally, NoCs are composed of electrical links that exhibit constrained bandwidth, increased energy consumption at high-speed communication, and long latencies. Photonic NoCs (PNoCs) have been shown to provide high bandwidth at low latencies and negligible data-dependent power. However, the power overheads of lasers, thermal tuning, and electrical-optical conversion present major challenges against wide-scale adoption of PNoCs. A primary factor that impacts PNoC power is the number of activated laser wavelengths in the system. Applications’ dynamic bandwidth needs provide the opportunity to selectively deactivate laser wavelengths when there is a lower bandwidth demand to alleviate high PNoC power concerns. This article analyzes dynamic PNoC activity of applications at runtime so as to select laser wavelengths depending on an application’s bandwidth requirements. The article then proposes PROWAVES , a proactive runtime wavelength selection policy that forecasts the bandwidth needs and activates the minimum laser wavelengths for each application phase. We develop a cross-layer simulation framework to model the system performance, PNoC power and transient thermal distribution in a manycore system with PNoCs. We compare PROWAVES with prior system-level policies and our simulation results on a 2.5-D system demonstrate that PROWAVES provides 18% and 33% power savings with only 1% and 5% loss in performance, respectively, compared to activating all laser wavelengths in the system.