A versatile directory scheme (Dir/sub 2/NB+L) and its implementation on BY91-1 multiprocessors system

Cache coherence and synchronization between processors have been two critical issues in designing a shared memory multiprocessors system. From the perspective of hardware design, a directory based cache coherence protocol and lock mechanism are employed to prevent inconsistency of caches and warrant atomic memory accesses. The BY91-1 multiprocessors efficiently integrate supports for cache coherence and hardware based primitives by using a uniform directory scheme which is dubbed as Dir/sub 2/NB+L. This integration allows for low hardware overhead while maintaining both a coherent caches system and indivisible memory accesses in a scalable and cohesive fashion. This paper describes the design and rationale of this versatile directory scheme. Results on the evaluation of different directory schemes based on a preliminary simulator-CASIMU demonstrate that Dir/sub 2/NB+L scheme is cost-effective. We also report on the experience gained by implementing this directory scheme on BY91-1 multiprocessors system. We believe that this scheme is well suited for CC-NUMA architecture.