MULTIPROCESSING SYSTEM EMPLOYING PENDING TAGS TO MAINTAIN CACHE COHERENCE

摘要

A pending tag system and method to maintain data coherence in a processing node during pending transactions in a transaction pipeline. A pending tag storage unit may be coupled to a cache controller and configured to store pending tags each indicative of a coherence state for a data line corresponding to a pending transaction within the transaction pipeline. The pending tag storage unit includes a total amount of storage which is substantially less than an amount required to store tags contained in the full tag array for the cache memory. When a pending tag exists in the pending tag storage unit, the coherence state of the corresponding data line within the cache memory is dictated by the pending tag for snoop operations. Accordingly, data coherence is maintained during the period when transactions are pending, e.g., not yet presented to a processor and cache. When a pending transaction is completed, the coherence state of the corresponding data line as indicated by the full tag array may be overwritten by the coherence state as indicated by the pending tag and the pending tag may deleted from the pending tag storage.