I know there have been some changes in this area, but this seems like a remaining bug.
Run top. Press S to show system processes. Observe idle1 and idle3 (the hyperthreaded idles) stuck at 100%. With 0:00 time. Now if you switch hw.smt=1 the 100% slowly ticks down, but the time immediately jumps up to many hours. Just a peculiarity I noticed. Perhaps there's some way to consolidate special cases?
