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Improved Sharing of Modified Lines in Tightly-Coupled Multiprocessor Configurations

IP.com Disclosure Number: IPCOM000056999D
Original Publication Date: 1988-Feb-01
Included in the Prior Art Database: 2005-Feb-14

Publishing Venue

IBM

Related People

Authors:
Emma, PG Knight, JW Pomerene, JH Rechtschaffen, RN Sparacio, RJ [+details]

Abstract

A technique is described whereby, in a multiprocessing computer system, cache lines which contain changing shared data can be detected using "ghost" hits. The store updates to these lines can be performed in a more timely manner and their contents made accessible in caches where they are invalid. An important distinction exits between cache lines that are absent from the cache and cache lines that are present in the cache but invalid. When a processor accesses its cache and finds that the line it is accessing has been invalidated by some action involving another central processing unit (CPU) or channel, a "ghost" hit is said to have occurred. Properly managed, the existence of "ghost" hits can serve as a basis for reducing the penalty for sharing modified lines in tightly- coupled configurations.