Computer system including plural caches and utilizing access history or patterns to determine data ownership for efficient handling of software locks

摘要

A system and method for enabling a multiprocessor system employing a memory hierarchy to identify data units or locations being used as software locks. The memory hierarchy comprises a main memory having a plurality of data units, a plurality of caches that operate independently of each other, and at least one coherent domain interfaced to each cache. Each coherent domain comprises at least two processors. The main memory maintains coherency of data among the plurality of caches using a directory that maintains information about each data line. The system of the present invention allows a requesting agent, such as a processor or cache, to request a data unit without specifying the type of ownership, where ownership may be exclusive or shared. The directory includes history information that defines the previous access pattern of the requested data unit. Prior to forwarding the requested data unit to the requesting agent, the main memory checks, using a conditional fetch command, the history information to determine what type of ownership to associate with the requested data unit. The requested data unit is then delivered to the requesting agent with ownership rights specified by the history information. The processors may utilize a directory-based protocol such as MESI (modified, exclusive, shared, invalid) to maintain coherence among the processors, with each processor snooping a shared bus to track the status of caches lines in the other processors.