Exploring the Design Space for a Shared-Cache Multiprocessor

In the near future, semiconductor technology will allow the integration of multiple processors on a chip or multichipmodule (MCM). In this paper we investigate the architecture and partitioning of resources between processors and cache memory for single chip and MCM-based multiprocessors. We study the performance of a cluster-based multiprocessor architecture in which processors within a cluster are tightly coupled via a shared cluster cache for various processor-cache configurations. Our results show that for parallel applications, clustering via shared caches provides an effective mechanism for increasing the total number of processors in a system, without increasing the number of invalidations. Combining these results with cost estimates for shared cluster cache implementations leads to two conclusions: 1) For a four cluster multiprocessor with single chip clusters, two processors per cluster with a smaller cache provides higher performance and better cost/ performance than a single processor with a larger cache and 2) this four cluster configuration can be scaled linearly in performance by adding processors to each cluster using MCM packaging techniques.