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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.
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 ...
Transactional memory model [7] is the combination of cache coherency and memory consistency models as a communication model for shared memory systems supported by software or hardware; a transactional memory model provides both memory consistency and cache coherency. A transaction is a sequence of operations executed by a process that ...
– The cache is set M (D) if the "shared line" is off, otherwise is set O (SD). All the other copies are set S (V) Cache in E (R) or M (D) state (exclusiveness) – The write can take place locally without any other action. The state is set (or remains) M (D) Write Miss – Write Allocate – Read with Intent to Modified operation
If another cache has the block in the "M" state, it must write back the data to the backing store and go to the "S" or "I" states. 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.
Consider the case when L2 is exclusive 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 moved from the L2 cache to the L1 cache.
An optimal cache-oblivious algorithm is a cache-oblivious algorithm that uses the cache optimally (in an asymptotic sense, ignoring constant factors). Thus, a cache-oblivious algorithm is designed to perform well, without modification, on multiple machines with different cache sizes, or for a memory hierarchy with different levels of cache ...
In a cache implementation, the cache lines are generally augmented with read and write bits. When the hardware controller receives a request, the controller uses these bits to detect a conflict. If a serializability conflict is detected from a parallel transaction, then the speculative values are discarded.