A cache coherency protocol for optically connected parallel computer systems

A cache coherency protocol was developed for the Multiple Channel Architecture (MCA), a proposed computer architecture that uses an optical interconnection network to overcome many of the problems associated with internode communication in massively parallel systems. A directory-based protocol was attempted, but testing revealed a serious scalability problem associated with the collection of acknowledgement packets. An alternative scheme, which employs snooping on a special-purpose, time-division multiplexed optical channel performed well. Additionally, the benefits of a separate cache for shared data were examined. Simulations demonstrate that the coherency protocol improves system performance and scalability, and that additional performance gains may be attained by customizing shared cache parameters