Global Bus Design of a Bus-Based COMA Multiprocessor DICE

DICE is a shared-bus multiprocessor based on a distributed shared-memory architecture, known as Cache-Only Memory Architecture (COMA). Unlike previous COMA proposals for large-scale multiprocessing, DICE utilizes the COMA to effectively decrease the gap between modern high-performance microprocessors and the bus. As microprocessors become faster and demand more bandwidth, the already limited scalability of a shared bus decreases even further. DICE tries to optimize the COMA for a shared-bus medium, in particular to reduce detrimental effects of the cache coherence and the “last memory block” problem on replacement. In this paper, we present a global bus design for a bus-based COMA multiprocessor using the IEEE Futurebus+ standard backplane bus and the Texas Instruments chip-set. Our design demonstrates that necessary bus transactions for DICE can be done efficiently with existing standard bus signals. Considering the benefits of the COMA and the little design complexity it adds to the conventional shared-bus multiprocessor design, a bus-based COMA multiprocessor such as DICE can become a viable candidate for future shared-bus multiprocessor designs.