Electro-Photonic NoC Designs for Kilocore Systems

Abstract

The increasing core count in manycore systems requires a corresponding large Network-on-chip (NoC) bandwidth to support the overlying applications. However, it is not possible to provide this large bandwidth in an energy-efficient manner using electrical link technology. To overcome this issue, photonic link technology has been proposed as a replacement. This work explores the limits and opportunities for using photonic links to design the NoC architecture for a future Kilocore system. Three different NoC designs are explored: ElecNoC, an electrical concentrated two-dimensional- (2D) mesh NoC; HybNoC, an electrical concentrated 2D mesh with a photonic multi-crossbar NoC; and PhotoNoC, a photonic multi-bus NoC. We consider both private and shared cache architectures and, to leverage the large bandwidth density of photonic links, we investigate the use of prefetching and aggressive non-blocking caches. Our analysis using contemporary Big Data workloads shows that the non-blocking caches with a shared LLC can best leverage the large bandwidth of the photonic links in the Kilocore system. Moreover, compared to ElecNoC-based and HybNoC-based Kilocore systems, a PhotoNoC-based Kilocore system achieves up to 2.5× and 1.5× better performance, respectively, and can support up to 2.1× and 1.1× higher bandwidth, respectively, while dissipating comparable power in the overall system.