With regard to the necessity of setting CPU affinities so that processors marked for tickless operation do not acquire more than one process, wouldn't something like systemd ease the related administrative work? After all, I don't want to be messing around with taskset(1) on my laptop.
Also, how does this relate to CPU hyperthreads? Can a hyperthread be in tickless mode while a sibling hyperthread is not? Or must the entire core be woken up (or not) by the timer ticks?