Cache lines, false sharing and alignment

Question

I wrote the following short C++ program to reproduce the false sharing effect as described by Herb Sutter:

Say, we want to perform a total amount of WORKLOAD integer op

Answer 1

You should be able to request the required alignment from the compiler:

alignas(64) int arr[PARALELL * PADDING]; // align the array to a 64 byte line

Answer 2

gcc supports an aligned keyword: http://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html

You probably want something like this:

int arr[PARALLEL * 16] __attribute__ ((aligned (8)));

This aligns arr to an eight-byte boundary.

Visual Studio has a similar feature, too: http://msdn.microsoft.com/en-us/library/83ythb65.aspx

Answer 3

In modern C++ (17 and above) you should use hardware_constructive_interference_size.