Patent ID: 6088769
Filing Date: 2000-07-11
Classification: G06F

Abstract:
A method for maintaining cache coherence in a tightly coupled multiprocessor system having a plurality of nodes coupled to an interconnecting bus and storing portions of shared data, each node having a cache, a local coherence unit, a memory device and a processor device, the memory and processor device being coupled to form a memory/processor pair, the processor device within each node being capable of accessing data from the local memory device, the local cache, or over the interconnecting bus, from a non-local memory device, or a non-local cache, the method including the steps of:(a) checking a local coherence unit to determine with a single data entry in a table whether a most current copy of a requested portion of data is stored locally, in response to a request by a requesting processor associated with that local coherence unit for the requested portion of data:(b) if the most current copy of the requested portion of data is not stored locally, then checking a global coherence unit to determine in which node the most current copy of the requested portion of data is stored for addresses of the requested data;(c) sending a message to the requesting node from the global coherence unit indicating in which node the most current copy of the requested data is stored;(d) sending a request to transfer data from the requesting node to the node in which the most current copy of the requested data is stored; and(e) transferring to the requesting node, in response to the request to transfer, the most current copy of the requested data.