Method for maintaining cache coherence in a multiprocessor computer system

A method for maintaining cache coherence in a multiprocessor computer system having a potential for duplication of data in a plurality of storage locations identifiable as coherence blocks, said multiprocessor computer system employing doubly-linked lists for identifying a previous master of said data and a next master of said data, said method comprising the steps of:

• a) issuing from a first master to a second master a first transaction requesting sharable data in a coherence block of said second master, said second master being a repository of known valid data, said first transaction including at least an address of a requested coherence block, a first master address for said first master and a first index which identifies a storage location within the first master;
• b) storing a second master address of said second master and a second index of said second master in a previous master storage location of said first master, thereby to indicate a previous link of said first master;
• thereafter
• c) issuing from said second master to said first master a second transaction containing at least a portion of the sharable data and at least a third master address and a third index of a third master from a next master storage location of said second mater;
• thereafter
• d) storing said first master address and said first index in said next master storage location of said second master, thereby to indicate a next link of said second master;
• e) storing said third master address and said third index in a next master storage location of said first master, thereby to indicate a next link of said first master;
• thereafter
• f) issuing from said first master to said third master a third transaction containing said first master address and said first index;
• g) storing said first master address and said first index in a previous master storage location of said third master thereby to indicate a previous link of said third master;
• and
• h) updating previous master addresses and indexes and next master addresses and indexes in selected linked masters.

A method for maintaining cache coherence in a multiprocessor computer system having a potential for duplication of data in a plurality of storage locations identifiable as coherence blocks, said multiprocessor computer system employing doubly-linked lists for identifying a previous master of said data and a next master of said data, wherein a second master address and a second index are stored in a next master storage location of a second master, said method comprising the steps of:

• a) issuing from a first master to said second master a first transaction requesting sharable data in a coherence block of said second master, said second master being a repository of known valid data, said first transaction including at least an address of a requested coherence block, a first master address for said first master and a first index which identifies a data storage location within the first master;
• b) storing said second master address of said second master and said second index of said second master in a previous master storage location of said first master, thereby to indicate a previous link of said first master;
• thereafter
• c) issuing from said second master to said first master a second transaction containing at least a portion of the sharable data and at least said second master address and said second index from the next master storage location of said second master;
• thereafter
• d) storing said first master address and said first index in said next master storage location of said second master, thereby to indicate a next link of said second master;
• e) storing said second master address and said second index in a next master storage location of said first master, thereby to indicate a next link of said first master;
• and thereafter
• f) updating previous master addresses and indexes and next master addresses and indexes in selected linked masters to correct pointers.

A method for maintaining cache coherence in a multiprocessor computer system having a potential for duplication of data in a plurality of storage locations identifiable as coherence blocks, said multiprocessor computer system employing doubly-linked lists for identifying a previous master of said data and a next master of said data, said method comprising the steps of:

• a) issuing from a first master to a second master a first transaction requesting a purge of sharable data in a coherence block of the first master, said first transaction including a third master address for a third master and a third index which identifies a data storage location within the third master;
• thereafter
• b) storing said third master address and third index in a next master storage location of said second master, thereby to indicate a next link of said second master;
• c) issuing from said second master to said third master a second transaction, said second transaction containing a second master address and a second index of said second master;
• thereafter
• d) issuing from said third mast to said first master a third transaction acknowledging completion of said first transaction;
• thereafter
• e) storing said second master address and said second index in a previous master storage location of said third master, thereby to indicate a previous link of said third master;
• and
• f) marking said coherence block of said first master as invalid.