I often hear Prefetching as a technique for speeding up, for example, sequential memory access pattern. The prefetch should occur sufficiently far ahead in time to mitigate the latency of memory access, for example in a loop traversing memory linearly.

According to the famous "What Every Programmer Should Know About Memory" paper by Ulrich Drepper, it is written:

This prefetching would remove some of the costs of accessing main memory since it happens asynchronously with respect to the execution of the program

(emphasis mine)

I could not find references on Google or Wikipedia corroborating or proving this. Does anyone know where I can find if this is true?

The only reasoning I can think of is rhetorical: it must be asynchronous b/c otherwise prefetching offers no benefit to sequential access... unless the execution time of prefetching a cache line is less than bypassing prefetch and placing the same cache line from RAM directly into cache.


1 Answer 1


If it is implemented in hardware, prefetching is typically done asynchronously.

It's also possible for a compiler to insert extra prefetch instructions into the code. Thus, the initiation of the fetch is done synchronously, but then the memory access continues asynchronously.

See https://en.wikipedia.org/wiki/Cache_prefetching.


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