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Cache placement policies are policies that determine where a particular memory block can be placed when it goes into a CPU cache.A block of memory cannot necessarily be placed at an arbitrary location in the cache; it may be restricted to a particular cache line or a set of cache lines [1] by the cache's placement policy.
Once the cache block is in the Modified (M) state and there is a bus read (BusRd) request, the block flushes (Flush) the modified data and changes the state to owned (O), thus making it the sole owner for that particular cache block. At the same time, when it is in the modified (M) state, there is never going to be a bus write request (BusUpgr ...
This cache does not have permission to modify the copy. Unlike the MESI protocol, a shared cache line may be dirty with respect to memory; if it is, one cache has a copy in the Owned state, and that cache is responsible for eventually updating main memory. If no cache holds the line in the Owned state, the memory copy is up to date.
Once any "M" line is written back, the cache obtains the block from either the backing store, or another cache with the data in the "S" state. The cache can then supply the data to the requester. After supplying the data, the cache block is in the "S" state. When a write request arrives at a cache for a block in the "M" state, the cache ...
- If there is a copy in another cache, the "Shared line" is set "on" - If the "Shared Line" is "on" the cache is set SD, else D. All the other caches possible copy are set SC. Write Miss - Like with Read Miss, the data comes from the "owner", D or SD or from MM, then the cache is updated - If there is a copy in another cache, the "Shared line ...
In this protocol, each block in the local cache is in one of these four states: Invalid: This block has an incoherent copy of the memory. Valid: This block has a coherent copy of the memory. The data may be possibly shared, but its content is not modified. Reserved: The block is the only copy of the memory, but it is still coherent. No write ...
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Cache coherence is the discipline which ensures that the changes in the values of shared operands (data) are propagated throughout the system in a timely fashion. [2] The following are the requirements for cache coherence: [3] Write Propagation Changes to the data in any cache must be propagated to other copies (of that cache line) in the peer ...