Balancing Performance and Cost in CMP Interconnection Networks

This paper presents an innovative router design, called Rotary Router, which successfully addresses CMP cost/performance constraints. The router structure is based on two independent rings, which force packets to circulate either clockwise or counterclockwise, traveling through every port of the router. These two rings constitute a completely decentralized arbitration scheme that enables a simple, but efficient way to connect every input port to every output port. The proposed router is able to avoid network deadlock, livelock, and starvation without requiring data-path modifications. The organization of the router permits the inclusion of throughput enhancement techniques without significantly penalizing the implementation cost. In particular, the router performs adaptive routing, eliminates HOL blocking, and carries out implicit congestion control using simple arbitration and buffering strategies. Additionally, the proposal is capable of avoiding end-to-end deadlock at coherence protocol level with no physical or virtual resource replication, while guaranteeing in-order packet delivery. This facilitates router management and improves storage utilization. Using a comprehensive evaluation framework that includes full-system simulation and hardware description, the proposal is compared with two representative router counterparts. The results obtained demonstrate the Rotary Router's substantial performance and efficiency advantages.