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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.
A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. [1] A cache is a smaller, faster memory, located closer to a processor core, which stores copies of the data from frequently used main memory locations.
The 3Cs group of cache misses can be extended to 4Cs when a multi-processor system with cache is involved, the fourth C being coherence misses. The coherence miss count is the number of memory accesses that miss because a cache line that would otherwise be present in the thread's cache has been invalidated by a write from another thread. [3]
The prefetch should occur sufficiently far ahead in time to mitigate the latency of memory access, for example in a loop traversing memory linearly. The GNU Compiler Collection intrinsic function __builtin_prefetch can be used to invoke this in the programming languages C or C++.
Modern programming languages mainly assume two levels of memory, main memory and disk storage, though in assembly language and inline assemblers in languages such as C, registers can be directly accessed. Taking optimal advantage of the memory hierarchy requires the cooperation of programmers, hardware, and compilers (as well as underlying ...
Some programming languages (such as C) allow the programmer to suggest that certain variables be kept in registers. Data locality is a typical memory reference feature of regular programs (though many irregular memory access patterns exist). It makes the hierarchical memory layout profitable.
Most programming languages have some notion of a thread of execution which executes statements in a defined order. Traditional compilers translate high-level expressions to a sequence of low-level instructions relative to a program counter at the underlying machine level.
Cache prefetching can be accomplished either by hardware or by software. [3]Hardware based prefetching is typically accomplished by having a dedicated hardware mechanism in the processor that watches the stream of instructions or data being requested by the executing program, recognizes the next few elements that the program might need based on this stream and prefetches into the processor's ...