A localizing directory coherence protocol

Abstract

User-controllable coherence revives the idea of cooperation between software and hardware in an attempt to bridge the gap between efficient small-scale shared memory machines and massive distributed memory machines. It proposes a new multiprocessor architecture which has both a global address-space and multiple processor-local address-spaces with new memory instructions and a new coherence protocol to manage the dual address-spaces.The purpose of this paper is twofold. First, we solidify the semantics of instruction set extensions that enable "localization" -- the act of moving data from the global address-space to a processor's local address-space -- thus clearly defining the requirements for a localizing coherence protocol. Second, we demonstrate the feasibility of localizing coherence by describing the workings of a full-scale directory-based protocol that we have implemented and tested using an existing protocol specification tool.