On timing constraints of snooping in a bus-based COMA multiprocessor

Cache only memory architecture has the potential to decrease global bus traffic in shared-bus multiprocessors, thereby reducing the speed gap between modern microprocessors and global backplane bus systems. However, the (huge) size of attraction memory (AM) in each processor node makes it difficult to properly match the access time of its state and tag storage to the bus cycle. This becomes a serious burden in efficient snooping, much more than in conventional shared-bus multiprocessors, especially when a high bus clock frequency is used. In this paper, we propose a scheme to relax the timing constraints of snooping in a bus-based COMA multiprocessor, which allows an efficient design of a global bus protocol, and a cost-effective implementation of the overall system by using slower and cheaper memory for the state and tag storage of AM.