A Case for Handshake in Nanophotonic Interconnects

Nanophotonics has been proposed to design low latency and high bandwidth NOC for future Chip Multi-Processors (CMPs). Recent nanophotonic NOC designs adopt the token-based arbitration coupled with credit-based flow control, which leads to low bandwidth utilization. In this work, we propose two handshake schemes for nanophotonic interconnects in CMPs, Global Handshake (GHS) and Distributed Handshake (DHS), which get rid of the traditional credit-based flow control, reduce the average token waiting time, and finally improve the network throughput. Furthermore, we enhance the basic handshake schemes with setaside buffer and circulation techniques to overcome the Head-Of-Line (HOL) blocking. Our evaluation shows that the proposed handshake schemes improve network throughput by up to 62% under synthetic workloads. With the extracted trace traffic from real applications, the handshake schemes can reduce the communication delay by up to 59%. The basic handshake schemes add only 0.4% hardware overhead for optical components and negligible power consumption. In addition, the performance of the handshake schemes is independent of on-chip buffer space, which makes them feasible in a large scale nanophotonic interconnect design.