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.
在我的应用程序中，我需要在一个大的连续内存数据块（100个MB）上执行计算。我想的是继续预取我的程序将来会触及的块的部分，这样当我对该部分执行计算时，数据已经在缓存中。
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.
有人能给我一个简单的例子来说明如何用gcc实现这个目标吗？我在某处读过_mm_prefetch，但不知道如何正确使用它。另请注意，我有一个多核系统，但每个核心将并行处理不同的内存区域。
2 个解决方案
#1
17
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.
gcc使用内置函数作为低级指令的接口。特别是对于你的情况__builtin_prefetch。但是，在访问模式不易自动预测的情况下，使用它时，您应该看到可测量的差异。
#2
15
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.
现代CPU具有相当不错的自动预取功能，如果您尝试启动软件预取，您可能会发现弊大于利。如果您发现实际上存在性能问题，那么很可能会有更多“低挂果”，您可以专注于优化。当你急需几个百分点的吞吐量时，预取往往是你可能会尝试的最后一件事。
#1
17
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.
gcc使用内置函数作为低级指令的接口。特别是对于你的情况__builtin_prefetch。但是，在访问模式不易自动预测的情况下，使用它时，您应该看到可测量的差异。
#2
15
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.
现代CPU具有相当不错的自动预取功能，如果您尝试启动软件预取，您可能会发现弊大于利。如果您发现实际上存在性能问题，那么很可能会有更多“低挂果”，您可以专注于优化。当你急需几个百分点的吞吐量时，预取往往是你可能会尝试的最后一件事。