c - Aligning to cache line and knowing the cache line size

Question

To prevent false sharing, I want to align each element of an array to a cache line. So first I need to know the size of a cache line, so I assign each element that amount of bytes. Secondly I want the start of the array to be aligned to a cache line.

I am using Linux and 8-core x86 platform. First how do I find the cache line size. Secondly, how do I align to a cache line in C. I am using the gcc compiler.

So the structure would be following for example, assuming a cache line size of 64.

element[0] occupies bytes 0-63
element[1] occupies bytes 64-127
element[2] occupies bytes 128-191

and so on, assuming of-course that 0-63 is aligned to a cache line.

Answer 1

I am using Linux and 8-core x86 platform. First how do I find the cache line size.

$ getconf LEVEL1_DCACHE_LINESIZE
64

Pass the value as a macro definition to the compiler.

$ gcc -DLEVEL1_DCACHE_LINESIZE=`getconf LEVEL1_DCACHE_LINESIZE` ...

At run-time sysconf(_SC_LEVEL1_DCACHE_LINESIZE) can be used to get L1 cache size.