3/22/2023 0 Comments Cache coherence![]() The introduction of the Owned state allows dirty sharing of data, i.e., a modified cache block can be moved around various caches without updating main memory. When this cache changes data on the cache line, it must broadcast those changes to all other caches sharing the line. Owned This cache is one of several with a valid copy of the cache line, but has the exclusive right to make changes to it-other caches may read but not write the cache line. Modified This cache has the only valid copy of the cache line, and has made changes to that copy. 2 ' System Programming', each cache line is in one of five states: In order for this to be possible, direct cache-to-cache transfers of data must be possible, so a cache with the data in the modified state can supply that data to another reader without transferring it to memory.Īs discussed in AMD64 Architecture Programmer's Manual Vol. While the data must still be written back eventually, the write-back may be deferred. ![]() This avoids the need to write modified data back to main memory before sharing it. ![]() In addition to the four common MESI protocol states, there is a fifth "Owned" state representing data that is both modified and shared. In computing, MOESI is a full cache coherency protocol that encompasses all of the possible states commonly used in other protocols. (For a detailed description see Cache coherency protocols (examples)) Short description: Cache coherence protocol, inludes Owned and Exlusive states as extensions of the MSI protocol.
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