A scalable cache coherent scheme exploiting wormhole routing networks

Abstract

Large scale shared memory multiprocessors favor a directory-based cache coherence scheme for its scalability. The directory space needed to record the information for sharers has a complexity of /spl Theta/(N/sup 2/) when a full-mapped vector is used for an N-node system. Though this overhead can be reduced by limiting the directory size assuming that the sharing degree is small, it will experience significant inefficiency when a data is widely shared. In this paper, we propose a new directory scheme and a cache coherence scheme based on it for a mesh interconnection. Deterministic and wormhole routing enables a pointer to represent a set of nodes. Also a message traversing on the mesh performs a broadcast mission to a set of nodes without extra traffic, which can be utilized for the cache coherence problem. Only a slight change on a generic router is needed to implement our scheme. This scheme is also applicable to any k-ary n-cube networks including a mesh.