In my application, at one point I need to perform calculations on a large contiguous block of memory data (100s of MBs). What I was thinking was to keep prefetching the part of the block my program will touch in future, so that when I perform calculations on that portion, the data is already in the cache.
Can someone give me a simple example of how to achieve this with gcc? I read _mm_prefetch somewhere, but don't know how to properly use it. Also note that I have a multicore system, but each core will be working on a different region of memory in parallel.
gcc uses builtin functions as an interface for lowlevel instructions. In particular for your case __builtin_prefetch. But you only should see a measurable difference when using this in cases where the access pattern is not easy to predict automatically.
Modern CPUs have pretty good automatic prefetch and you may well find that you do more harm than good if you try to initiate software prefetching. There is most likely a lot more "low hanging fruit" that you can focus on for optimisation if you find that you actually have a performance problem. Prefetch tends to be one of the last things that you might try, when you're desperate for a few more percent throughput.
来源：https://stackoverflow.com/questions/10323420/prefetching-data-to-cache-for-x86-64