International Business Machines Corporation

Michael P Witt

Michael Ignatowski

Lishing Liu

Matthew A Krygowski

Gregory Salyer

Donald W Price

Patrick M Gannon

Yee-Ming Ting

William K Rodiger

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).

Coherence control by data invalidation in selected processor caches

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Fishkill, NY, United States of America

Michael P Witt