does different cpus prefer different loop unrolling group size

[goastler]

e.g. 8 works nicely on my pc, 4 less so, 16 very much less so

[goastler]

• [ ] add macro which can set the unroll level to 2/4/8/16/32/64 (no need to go above 64 as we never do more iterations than that

[goastler]

yes it will be diff per cpu as the cache size varies, so the cache hits for different step sizes for unrolled loops are going to be different. Unroll too much and too many cpu instructions outweight the benefits, too few and you don't gain cache locality and branch overhead reduction