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Multiprocessor cache coherence directed by combined local and global tables

  • US 6,088,769 A
  • Filed: 10/01/1996
  • Issued: 07/11/2000
  • Est. Priority Date: 10/01/1996
  • Status: Expired due to Fees
First Claim
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1. 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.

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