Cache lines, false sharing and alignment
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
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