Patent ID: 7613885

Claim:
A cache coherency control method for a multi-processor system, in which the multi-processor system includes multiple nodes connected to each other via a system connection network, each node includes one or more processors, a node controller connected to the processors via a processor bus, and a memory unit, each memory unit has one of a plurality of main storage portions constituting part of a main storage shared by processors of the plurality of nodes, the processor has a cache to hold data retrieved from the memory unit, and the cache coherency control method comprising the steps of: holding, by each node controller, an address tag for data maintained in the cache of the processor, a cache copy tag for maintaining a cache state, and a cache copy tag management unit for managing the cache copy tag; receiving, by a first node controller of the node controllers, a cache miss request from the processor connected to the first node controller via the processor bus, broadcasting, by the first node controller, a snoop request to a second node controller of the node controllers other than the first node controller via the system connection network; determining, by the first node controllers, whether a snoop response corresponding to the snoop request is returned from one of the second node controllers; retrieving, by the first node controller, the cache copy tag held in the first node controller; issuing, by the cache copy tag management unit, an advanced response notification, via the processor bus to the processor, when the address is registered in the cache copy tag of the first node controller; and returning, by the first node controller, a response data obtained from the memory unit, via the processor bus, to the processor without a wait for counting a snoop result as a response of the broadcast snoop request from the second node controllers, when the snoop responses are collected from the second node controllers, counting, by the first node controller, a snoop result on the basis of the snoop responses.