Hierarchical cache/bus architecture for shared memory multiprocessors

A new, large scale multiprocessor architecture is presented in this paper. The architecture consists of hierarchies of shared buses and caches. Extended versions of shared bus multicache coherency protocols are used to maintain coherency among all caches in the system. After explaining the basic operation of the strict hierarchical approach, a clustered system is introduced which distributes the memory among groups of processors. Results of simulations are presented which demonstrate that the additional coherency protocol overhead introduced by the clustered approach is small. The simulations also show that a 128 processor multiprocessor can be constructed using this architecture which will achieve a substantial fraction of its peak performance. Finally, an analytic model is used to explore systems too large to simulate (with available hardware). The model indicates that a system of over 1000 usable MIPS can be constructed using high performance microprocessors.