Sharing aware snoop filter apparatus and method

A method comprising:

• allocating a first entry for a first cache line in a primary snoop filter, the first entry comprising a N unique identifiers to uniquely identify up to N caches currently storing the cache line;
• detecting that a number of caches currently storing the first cache line is greater than N;
• and
• responsively allocating a first auxiliary entry for the first cache line in an auxiliary snoop filter to uniquely identify one or more additional caches storing the cache line.

A system comprising:

• a memory to store instructions and data;
• a processor to execute the instructions and process the data;
• a graphics processor to perform graphics operations in response to graphics instructions;
• a network interface to receive and transmit data over a network;
• an interface for receiving user input from a mouse or cursor control device, the plurality of cores executing the instructions and processing the data responsive to the user input;
• the processor comprising:
• a plurality of caches, each of the caches comprising a plurality of cache lines, at least some of which are to be shared by two or more of the caches;
• a snoop filter to monitor accesses to the plurality of cache lines shared by the two or more caches, the snoop filter comprising:
• a primary snoop filter comprising a first plurality of entries, each entry associated with one of the plurality of cache lines and comprising a N unique identifiers to uniquely identify up to N of the plurality of caches currently storing the cache line;
• an auxiliary snoop filter comprising a second plurality of entries, each entry associated with one of the plurality of cache lines, wherein once a particular cache line has been shared by more than N caches, an entry for that cache line is allocated in the auxiliary snoop filter to uniquely identify one or more additional caches storing the cache line.