Scalable multiprocessor system and cache coherence method incorporating invalid-to-dirty requests

Abstract

An invalid-to-dirty request permits a transition from an invalid memory state to a dirty state without requiring an up-to-date copy of the memory. The present invention is a system for supporting invalid-to-dirty memory transactions in an aggressive cache coherence protocol that minimizes directory entry locking. The nodes of a multiprocessor system each include a protocol engine that is configured to implement a distinct invalidation request that corresponds to an invalid-to-dirty memory transaction. If node O receives this distinct invalidation request while waiting for a response to an outstanding request for exclusive ownership, the protocol engine of node O is configured to treat the distinct invalidation request as applying to the memory line of information that is the subject of the outstanding request for exclusive ownership. Furthermore, if the node O receives a normal invalidation request, while it has an outstanding exclusive request, the invalidation request applies to a previous copy of the memory line of information held by the node N and therefore the protocol engine of node O is configured to ignore the normal invalidation request in this circumstance.