NetCache: A Network/Cache Hybrid for Multiprocessors

In this paper we propose the use of an optical network not only as the communication medium, but also as a system-wide cache for the shared data in a multiprocessor. More specifically, the basic idea of our novel network/cache hybrid (and associated coherence protocol), called NetCache, is to use an optical ring network on which some amount of recently-accessed shared data is continually sent around. These data are organized as a cache shared by all processors. We use detailed execution-driven simulations of a dozen applications to evaluate a multiprocessor based on our NetCache architecture. We compare a 16-node multiprocessor with a third-level NetCache against three highly-efficient systems based on the DMON and LambdaNet optical interconnects. Our results demonstrate that the NetCache multiprocessor outperforms the DMON systems consistently for our applications; running time differences can be as significant as 105%. The NetCache system also compares favorably against the LambdaNet multiprocessor. For nine of our applications, the running time advantage of the NetCache machine ranges from 7% for applications with little data reuse in the shared cache to 79% for applications with significant data reuse. For the other applications, the two systems perform similarly. Based on these results and on our parameter space study, our main conclusion is that the NetCache is highly efficient under most architectural assumptions and for most applications.