I'm not an expert, I'm a lowly systems admin-

But I imagine the difference is that size of systemd itself and how mysql does fork().

SystemD is 1.5MB itself on my systems where I have it, but upstart (for example) is 148KB on centos 6.

Since an AMD Epyc has roughly 64Mb of L3 Cache, a larger binary would not have to be evicted from L3 cache as often.

One of Intels generally powerful all-rounder CPUs (2687Wv4) only has 30Mb of "Smart-cache" (which is fancy speak for; not that much)

A complete guess on my part though..