Cache inclusion policy
Usage methods of multi-level caches
Multi-level caches can be designed in various ways depending on whether the content of one cache is present in other levels of caches. If all blocks in the higher level cache are also present in the lower level cache, then the lower level cache is said to be inclusive of the higher level cache. If the lower level cache contains only blocks that are not present in the higher level cache, then the lower level cache is said to be exclusive of the higher level cache. If the contents of the lower level cache are neither strictly inclusive nor exclusive of the higher level cache, then it is called non-inclusive non-exclusive (NINE) cache.
Inclusive Policy
Consider an example of a two level cache hierarchy where L2 can be inclusive, exclusive or NINE of L1. Consider the case when L2 is inclusive of L1. Suppose there is a processor read request for block X. If the block is found in L1 cache, then the data is read from L1 cache and returned to the processor. If the block is not found in the L1 cache, but present in the L2 cache, then the cache block is fetched from the L2 cache and placed in L1. If this causes a block to be evicted from L1, there is no involvement of L2. If the block is not found in either L1 or L2, then it is fetched from the main memory and placed in both L1 and L2.
Begin with the source’s own compact description: “Cache inclusion policy” is usage methods of multi-level caches. The dossier treats that line as a proposition to test through Cache, inclusion and policy, not as a finished interpretation.
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