|
MOESI Protocol
Modified Owned Exclusive Shared Invalid (MOESI) is a full cache coherency protocol that encompasses all of the possible states commonly used in other protocols. In addition to the four common MESI protocol states, there is a fifth "Owned" state representing data that is both modified and shared. This avoids the need to write modified data back to main memory before sharing it. While the data must still be written back eventually, the write-back may be deferred . 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. As discussed in AMD64 Architecture Programmer's Manual Vol. 2 ''System Programming'', each cache line is in one of five states: ;Modified: This cache has the only valid copy of the cache line, and has made changes to that copy. The cached copy may be further modified freely. ;Owned: This line is one of seve ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of Cache Coherency Protocols
Examples of coherency protocols for cache memory are listed here. For simplicity, all "miss" Read and Write status transactions which obviously come from state "I" (or miss of Tag), in the diagrams are not shown. They are shown directly on the new state. Many of the following protocols have only historical value. At the moment the main protocols used are the R-MESI type / MESIF protocols and the HRT-ST-MESI (MOESI type) or a subset or an extension of these. Cache coherency problem In systems as Multiprocessor system architecture#Symmetric multiprocessor system, Multiprocessor system, Multi-core processor, multi-core and Non-uniform memory access, NUMA system, where a dedicated cache for each ''processor'', ''core'' or ''node'' is used, a consistency problem may occur when a same data is stored in more than one cache. This problem arises when a data is modified in one cache. This problem can be solved in two ways: # Invalidate all the copies on other caches (broadcast-invalida ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
