Efficient and scalable cache coherence schemes for shared memory hypercube multiprocessors

Abstract

Large scale shared memory multiprocessors use a directory based cache coherence scheme. The basic directory scheme, called full-map, is efficient but has a large memory overhead. Therefore, limited directory schemes have been proposed which limit the number of pointers in the directories. These schemes tradeoff smaller memory overhead for larger memory access latencies. We propose a new limited directory scheme, which achieves lower memory overhead as well as smaller memory access latencies. The scheme uses ring embedding in a hypercube in conjunction with wormhole routing to reduce the invalidation delays. The proposed scheme performs as good as full-map for smaller degree of sharing and performs better than full-map for larger degree of sharing.