> std::hardware_destructive_interference_size Exists so you don't have to guess, although in practice it'll basically always be 64.

Unfortunately it's not quite true, do to e.g. spacial prefetching [0]. See e.g. Folly's definition [1].

[0] https://community.intel.com/t5/Intel-Moderncode-for-Parallel...

[1] https://github.com/facebook/folly/blob/d2e6fe65dfd6b30a9d504...