C++ cache aware programming

Question

is there a way in C++ to determine the CPU's cache size? i have an algorithm that processes a lot of data and i'd like to break this data down into chunks such that they fit into the cache. Is this possible? Can you give me any other hints on programming with cache-size in mind (especially in regard to multithreaded/multicore data processing)?

Thanks!

Answer 1

You can see this thread: http://software.intel.com/en-us/forums/topic/296674

The short answer is in this other thread:

On modern IA-32 hardware, the cache line size is 64. The value 128 is a legacy of the Intel Netburst Microarchitecture (e.g. Intel Pentium D) where 64-byte lines are paired into 128-byte sectors. When a line in a sector is fetched, the hardware automatically fetches the other line in the sector too. So from a false sharing perspective, the effective line size is 128 bytes on the Netburst processors. (http://software.intel.com/en-us/forums/topic/292721)

Answer 2

The cache will usually do the right thing. The only real worry for normal programmer is false sharing, and you can't take care of that at runtime because it requires compiler directives.

Answer 3

Depending on what you're trying to do, you might also leave it to some library. Since you mention multicore processing, you might want to have a look at Intel Threading Building Blocks.

TBB includes cache aware memory allocators. More specifically, check cache_aligned_allocator (in the reference documentation, I couldn't find any direct link).