UNION: A unified inter/intra-chip optical network for chip multiprocessors

As modern computing systems become increasingly complex, communication efficiency among and inside chips has become as important as the computation speeds of individual processor cores. Traditionally, inter-chip and intra-chip communication architectures are separately designed to maximize design flexibility under different constraints. However, jointly designing communication architectures for both inter-chip and intra-chip communication could potentially yield better solutions. In this paper, we present a unified inter/intra-chip optical network, called UNION, for chip multiprocessors (CMP). UNION is based on recent progress in nano-photonic technologies. It connects not only processors on a single CMP but also multiple CMPs in a system. UNION employs a hierarchical optical network to separate inter-chip communication traffic from intra-chip communication traffic. It fully utilizes a single optical network to transmit both payload packets and control packets. The network controller on each CMP not only manages intra-chip communications but also collaborate with each other to facilitate inter-chip communications. We compared CMPs using UNION with those using a matched electronic counterpart in 45 nm process. Based on eight applications, simulation results show that on average UNION improves CMP performance by 3.1X while reducing 92% of network energy consumption and 52% of communication delay.