While shoring up nomenclature: I believe “simultaneous multi-threading” (SMT) is the generic term and “Hyperthreading” is Intel’s branding of their SMT implementation.

Calling AMD’s SMT “hyperthreading” is like calling all tissues Kleenex. It’s fine imo, but it doesn’t hurt to know these things.

It was worse than even that, several parts of the build process were fully sequential. I only got benefit of multiple cores at all because the tooling in those sequential steps were utilizing it, or related system services were.

But, yes, I also did change at least one config to allow it to spawn more than 2 threads.

Yepp, SMT is the generic term also used in academia for ages. Source: Old editions of venerable "Computer Architecture" by Hennessy & Patterson.