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Cache hierarchy, or multi-level cache, is a memory architecture that uses a hierarchy of memory stores based on varying access speeds to cache data. Highly requested data is cached in high-speed access memory stores, allowing swifter access by central processing unit (CPU) cores.
For example, the level-1 data cache in an AMD Athlon is two-way set associative, which means that any particular location in main memory can be cached in either of two locations in the level-1 data cache. Choosing the right value of associativity involves a trade-off. If there are ten places to which the placement policy could have mapped a ...
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.
Since each cache block is of size 4 bytes and is 2-way set-associative, the total number of sets in the cache is 256/(4 * 2), which equals 32 sets. Set-Associative Cache. The incoming address to the cache is divided into bits for Offset, Index and Tag. Offset corresponds to the bits used to determine the byte to be accessed from the cache line.
Unsuccessful attempts to read or write data from the cache (cache misses) result in lower level or main memory access, which increases latency. There are three basic types of cache misses known as the 3Cs [2] and some other less popular cache misses.
Level 2 (L2) Instruction and data (shared) – 1 MiB [citation needed] [original research] in size. Best access speed is around 200 GB/s [9] Level 3 (L3) Shared cache – 6 MiB [citation needed] [original research] in size. Best access speed is around 100 GB/s [9] Level 4 (L4) Shared cache – 128 MiB [citation needed] [original research] in size.
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Diagram of a CPU memory cache operation. In computing, a cache (/ k æ ʃ / ⓘ KASH) [1] is a hardware or software component that stores data so that future requests for that data can be served faster; the data stored in a cache might be the result of an earlier computation or a copy of data stored elsewhere.