I believe parent means you can pack multiple unrelated counters intended for the same core. The cache line is still uncontended, you're just storing more in it.

I believe parent means you can pack multiple unrelated counters intended for the same core. The cache line is still uncontended, you're just storing more in it. If you're building these things up from scratch this should be obvious, but if you're pulling in a library it's easy to not realize how wasteful it is being.