Wavelength-Reused Hierarchical Optical Network on Chip Architecture for Manycore Processors

Abstract

Manycore processor is becoming the mainstream platform for cloud computing applications. However, the design of high-performance and sustainable inter-core communication network is still a challenging problem. Optical Network on Chip (ONoC) is an emerging chip-scale optical communication technology with high bandwidth capacity and energy efficiency. In this paper, we present a Wavelength Reused Hierarchical ONoC architecture, WRH-ONoC. It leverages the nonblocking wavelength-routed $\lambda$λ-router and hierarchical networking to reuse the limited number of wavelengths. In WRH-ONoC, all the cores are grouped into multiple subsystems, and the cores in the same subsystem are directly interconnected using a $\lambda$λ-router for nonblocking communication. For inter-subsystem communication, all subsystems are further connected through multiple $\lambda$λ-routers and gateways in a hierarchical manner. Thus, the available wavelengths can be reused in different $\lambda$λ-routers. Furthermore, WRHm-ONoC, an efficient extension with multicast ability is also proposed. Given the numbers of cores and available wavelengths, we derive the minimum hardware requirement, the expected end-to-end delay, and the maximum data rate. Theoretical analysis and simulation results indicate WRH-ONoC achieves prominent improvement on the communication performance and sustainability, e.g., 46.0 percent of reduction on zero-load delay and 72.7 percent of improvement on throughput for 400 cores with the modest hardware/energy costs.