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OPTNET: a cost-effective optical network for multiprocessors

Abstract:

In this paper we propose the OPTNET, a novel optical network and associated coherence protocol for scalable multiprocessors. The network divides its channels into broadcast and point-to-point groups. The broadcast channels are used for memory block request, coherence, and synchronization transactions, while the point-to-point channels are utilized for memory block transfer operations. The three main distinguishing features of the OPTNET are: a) its broadcast channels behave well under high contention; b) its point-to-point channels do not require any access control mechanism; and c) it can achieve good communication performance at a low hardware cost. We use detailed execution-driven simulations of ten applications to evaluation a 16-node OPTNET-based multiprocessor. We compare our multiprocessor against highly-efficient systems based on the DMON and LambdaNet optical interconnects. Our results demonstrate that our system outperforms the DMON multiprocessors consistently for our applications, even though the OPTNET requires no more hardware than DMON. The comparison between our multiprocessor and the LambdaNet system shows performance differences that average 4% in favor of the LambdaNet. However, the LambdaNet requires a factor of p more hardware than the OPTNET, where p is the number of computational nodes in the multiprocessor. Based on these results, our main conclusion is that the combination of our network and coherence protocol strikes an excellent cost/performance ratio for scalable multiprocessors.