I think the intuition on processes vs threads was right: 1. The Arc use is a case (I believe! Am not a Rust'er!) of true sharing of references. The cacheline w

I think the intuition on processes vs threads was right: 1. The Arc use is a case (I believe! Am not a Rust'er!) of true sharing of references. The cacheline will be contention across cores. Doing processes would have eliminated true sharing. Tracking logical core affinity for references via a modal type system could have flagged this at compile time, but I suspect that's not a thing in Rust land. 2. Even if it was false sharing at the cacheline level, process abstractions in shared memory systems are generally aligned to avoid false sharing at cacheline granularity (and misaligned ops at smaller granularities). Of course, in the extreme, a 10X hero programmer may have tried to do amazing levels of bit packing and syscall hackery and thus break all those niceties, but that's the cleanup that everyone else in a team has to make the hero a 10Xer.