which is optimal a bigger block cache size or a smaller one?

Question

Given a cache size with constant capacity and associativity, for a given code to determine average of array elements, would a cache with higher block size be preferred?

Answer 1

From your example code we can't say either way as long as the hardware pre-fetcher can keep up a memory stream at maximum memory throughput.

In a random access scenario a shorter cache-line might be preferable as you then don't need to fill all the line. But the total amount of cached memory would go down as you need more circuits for tags and potentially more time for comparing.

So a compromise must be made Intel has chosen 64-bytes per line (and fetches 2 lines) others has chosen 32-bytes per line.