Re: Microsecond sleeps with select()

> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > A comment on microsecond delays using select(). Most Unix kernels run
> > at 100hz, meaning that they have a programmable timer that interrupts
> > the CPU every 10 milliseconds.
>
> Right --- this probably also explains my observation that some kernels
> seem to add an extra 10msec to the requested sleep time. Actually
> they're interpreting a one-clock-tick select() delay as "wait till
> the next clock tick, plus one tick". The actual delay will be between
> one and two ticks depending on just when you went to sleep.
>

The BSDI code would be pselect():

/*
* If poll wait was tiny, this could be zero; we will
* have to round it up to avoid sleeping forever. If
* we retry below, the timercmp above will get us out.
* Note that if wait was 0, the timercmp will prevent
* us from getting here the first time.
*/
timo = hzto(&atv);
if (timo == 0)
timo = 1;

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