LIBRA: Thermal and Process Variation Aware Reliability Management in Photonic Networks-on-Chip

Silicon nanophotonics technology is being considered for future networks-on-chip (NoCs) as it can enable high bandwidth density and lower latency with traversal of data at the speed of light. But, the operation of photonic NoCs (PNoCs) is very sensitive to on-chip temperature and process variations. These variations can create significant reliability issues for PNoCs. For example, a microring resonator (MR) may resonate at another wavelength instead of its designated wavelength due to thermal and/or process variations, which can lead to bandwidth wastage and data corruption in PNoCs. This paper proposes a novel run-time framework called LIBRA to overcome temperature- and process variation- induced reliability issues in PNoCs. The framework consists of (i) a device-level reactive MR assignment mechanism that dynamically assigns a group of MRs to reliably modulate/receive data in a waveguide based on the chip thermal and process variation characteristics; and (ii) a system-level proactive thread migration technique to avoid on-chip thermal threshold violations and reduce MR tuning/ trimming power by dynamically migrating threads between cores. Our simulation results indicate that LIBRA can reliably satisfy on-chip thermal thresholds and maintain high network bandwidth while reducing total power by up to 61.3 percent, and thermal tuning/trimming power by up to 76.2 percent over state-of-the-art thermal and process variation aware solutions.