Re: Microsecond sleeps with select()

> Bruce Momjian <pgman@candle.pha.pa.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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