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Cache invalidation is a process in a computer system whereby entries in a cache are replaced or removed.. It can be done explicitly, as part of a cache coherence protocol. In such a case, a processor changes a memory location and then invalidates the cached values of that memory location across the rest of the computer system.
Instead, invalidation messages simply enter an invalidation queue and their processing occurs as soon as possible (but not necessarily instantly). Consequently, a CPU can be oblivious to the fact that a cache line in its cache is actually invalid, as the invalidation queue contains invalidations that have been received but haven't yet been applied.
data is stored only in one cache but the data in memory is not updated (invalid, not clean). O =Owner or SD =Shared Dirty or SM =Shared Modified or T =Tagged. modified, potentially shared, owned, write-back required at replacement. data may be stored in more than a cache but the data in memory is not updated (invalid, not clean).
Cache control instructions are specific to a certain cache line size, which in practice may vary between generations of processors in the same architectural family. Caches may also help coalescing reads and writes from less predictable access patterns (e.g., during texture mapping ), whilst scratchpad DMA requires reworking algorithms for more ...
When a write operation is observed to a location that a cache has a copy of, the cache controller updates its own copy of the snooped memory location with the new data. If the protocol design states that whenever any copy of the shared data is changed, all the other copies must be "updated" to reflect the change, then it is a write-update protocol.
In computing, cache replacement policies (also known as cache replacement algorithms or cache algorithms) are optimizing instructions or algorithms which a computer program or hardware-maintained structure can utilize to manage a cache of information. Caching improves performance by keeping recent or often-used data items in memory locations ...
Each cache line is in one of the following states: "dirty" (has been updated by local processor), "valid", "invalid" or "shared". A cache line contains a value, and it can be read or written. Writing on a cache line changes the value. Each value is either in main memory (which is very slow to access), or in one or more local caches (which is ...
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.