Coherence control by data invalidation in selected processor caches without broadcasting to processor caches not having the data
Patent 5265232 Issued on November 23, 1993. Estimated Expiration Date: April 3, 2011. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
A coherence directory and its methods of operation are disclosed for private processor caches in a multiple processor system to control data coherence in the system. It provides cross-invalidate (XI) controls for the assignment of exclusive and public ownership to data units in the processor caches, including required cross-invalidation of data units among the processor caches to obtain data coherence in the system in an efficient manner. The coherence directory can be used in a multiple processor system with or without any shared second level (L2) cache, shared or private. When a shared L2 cache is used to improve system access time, the coherence directory can also be used as the second level directory for the shared L2 cache and eliminate the need for any additional L2 directory(s).
Other References
Censier et al., "A New Solution to Coherence Problems in Multicache Systems", IEEE Transactions on Computers, C-27 No. 12, Dec. 1978, pp. 1112-1118
Chaiken et al., "Directory-Based Cache Coherence in Large-Scale Multiprocessors", Computer, vol. 23, No. 6, Jun., 1990, pp. 49-5