Design of large-scale symmetric multiprocessors (SMPs) using parallel optical interconnects

Abstract

Summary form only given, as follows. We address the primary limitation of band-width demands for address transaction in future cache coherent symmetric multiprocessors (SMPs). As a solution, we propose a scalable optical address subnetwork called symmetric multiprocessor network (SYMNET). SYMNET, not only has the ability to pipeline address requests, but also multiple address requests from different processors can propagate through the address subnetwork simultaneously. This is in contrast to all electrical bus-based SMPs, where only a single request is broadcast on the physical address bus at any given point in time. The simultaneous propagation of multiple address requests in SYMNET increases the available address bandwidth and lowers the latency of the network, but the preservation of cache coherence can no longer be maintained with the usual fast snooping protocols. A modified snooping coherence protocol, coherence in SYMNET (COSYM) is introduced to solve the coherence problem. We evaluated COSYM with a subset of Splash-2 benchmarks and compared it with the electrical bus-based MOESI protocol. Our simulation studies have shown a 5-66% improvement in execution time for COSYM as compared to MOESI for various applications. Simulations have also shown that the average latency for a transaction to complete using COSYM protocol was 5-78% better than the MOESI protocol. SYM-NET improves system performance and scalability and that additional performance gains may be attained with further improvement in optical device technology.