Abstract: In a computer system having a plurality of processors with internal caches, a method for handling race conditions arising when multiple processors simultaneously write to a particular cache line. Initially, a determination is made as to whether the cache line is in an exclusive, modified, invalid, or shared state. If the cache line is in either the exclusive or modified state, the cache line is written to and then set to the modified state. If the cache line is in the invalid state, a Bus-Read-Invalidate operation is performed. However, if the cache line is in the shared state and multiple processors initiate Bus-Write-Invalidate operations, the invalidation request belonging to the first processor is allowed to complete. Thereupon, the cache line is sent to the exclusive state, data is updated, and the cache line is set to the modified state. The second processor receives a second cache line, updates this second cache line, and sets the second cache line to the modified state.

Abstract: A two-way set-associative cache memory includes both a set array and a data array in one embodiment. The data array comprises multiple elements, each of which can contain a cache line. The set array comprises multiple sets, with each set in the set array corresponding to an element in the data array. Each set in the set array contains information which indicates whether an address received by the cache memory matches the cache line contained in its corresponding element of the data array. The information stored in each set includes a tag and a state. The tag contains a reference to one of the cache lines in the data array. If the tag of a particular set matches the address received by the cache memory, then the cache line associated with that particular set is the requested cache line. The state of a particular set indicates the number of cache lines mapped into that particular set.

Abstract: A system and method for managing caches in a multiprocessor having multiple levels of caches. An inclusion architecture and procedure are defined through which the L2 caches shield the L1 caches from extraneous communication at the L2, such as main memory and I/O read/write operations. Essential inclusion eliminates special communication from the L1 cache to the L2, yet maintains adequate knowledge at the L2, regarding the contents of the L1, to minimize L1 invalidations. Processor performance is improved by the reduced communication and the decreased number of invalidations. The processors and L1 caches practice a store-in policy. The L2 cache uses inclusion bits to designate by cache line a relationship between the line of data in the L2 cache and the corresponding lines as they exist in the associated L1 caches. Communication and invalidations are reduced through a selective setting/resetting of the inclusion bits and related L2 interrogation practice.