A hybrid NoC design for cache coherence optimization for chip multiprocessors

On chip many-core systems, evolving from prior multi-processor systems, are considered as a promising solution to the performance scalability and power consumption problems. The long communication distance between the traditional multi-processors makes directory-based cache coherence protocols better solutions compared to bus-based snooping protocols even with the overheads from indirections. However, much smaller distances between the CMP cores enhance the reachability of buses, revitalizing the applicability of snooping protocols for cache-to-cache transfers. In this work, we propose a hybrid NoC design to provide optimized support for cache coherency. In our design, on-chip links can be dynamically configured as either point-to-point links between NoC nodes or short buses to facilitate localized snooping. By taking advantage of the best of both worlds, bus-based snooping coherency and NoC-based directory coherency, our approach brings both power and performance benefits.