Re: nanosleep() for shorted than schedule slice

[David Holland <dholland-tech%netbsd.org@localhost>]

On Sun, Jul 02, 2017 at 05:04:56PM -0700, John Nemeth wrote:
 > } > > I wonder if it would make sense for nanosleep(2) to check
 > } > > that requested sleeping time is shorter than a schedule
 > } > > slice, and if it is, spin the CPU instead of scheduling
 > } > > another process. Any opinion on this?
 > } > 
 > } > No, that's wrong. It's also been discussed before.
 > } 
 > } How is that wrong? It was always more or less the point of nanosleep.
 > 
 >      If you start spinning right after the start of a timeslice,
 > you could spin for close to an entire timeslice.  On a modern
 > multi-GHz CPU that's a tremendous number of wasted cycles (also
 > doesn't help power consumption).

...huh?

What does "right after the start of a timeslice" have to do with it?

Anyway, if the requested sleep time is "close to an entire timeslice"
then you obviously don't spin. Please don't manufacture nonsense
counterexamples.

-- 
David A. Holland
dholland%netbsd.org@localhost