Short waits with umwait

The kernel would need to resume the thread after the wait, as the deadline would certainly have passed. It could resume at the instruction, but that would break immediately so there would be no point -- unless sleeps longer than a scheduling interval were permitted, which seems unlikely.

But probably you would run this on an isolcpu, with nohz, and hope never to get scheduled out.

It appears I have not yet discovered a formula that guarantees no schedule breaks, ever. I would welcome enlightenment.