Patent
1995-05-17
1997-04-22
Chan, Eddie P.
395469, 395470, 395472, 395473, 395449, G06F 1208
Patent
active
056236328
ABSTRACT:
In a multiprocessor system having a plurality of bus devices coupled to a storage device via a bus, wherein the plurality of bus devices have a snoop capability, and wherein the plurality of bus devices have first and second caches, and wherein the plurality of bus devices utilize a modified MESI data coherency protocol, the system provides for reading of a data portion from the storage device into one of the plurality of bus devices, wherein the first cache associated with the one of the plurality of bus devices associates a special exclusive state with the data portion, and wherein the second cache associated with the one of the plurality of bus devices associates an exclusive state with the data portion, initiating, by the one of the plurality of bus devices, a write-back operation with respect to the data portion, determining if there are any pending snoops in the second cache, and changing the special exclusive state to a modified state if there are no pending snoops in the second cache. If there is a pending snoop in the second cache, a comparing of addresses of the pending snoop and the data portion is performed. The special exclusive state is changed to a modified state if the addresses are different. The special exclusive state indicates that a data portion is held in the primary cache in a shared state and that the data portion is held in the secondary in an exclusive state.
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Liu Pei-chun P.
Mayfield Michael J.
Reese Robert J.
Chan Eddie P.
England Anthony V. S.
International Business Machines - Corporation
Kim Hong C.
Kordzik Kelly K.
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