Re: No 100 HZ timer !

Oliver Xymoron
2001-04-11T18:44:24Z

On Mon, 9 Apr 2001, Alan Cox wrote:

> > > Its worth doing even on the ancient x86 boards with the PIT.
> >
> > Note that programming the PIT is sloooooooow and doing it on every timer
> > add_timer/del_timer would be a pain.
>
> You only have to do it occasionally.
>
> When you add a timer newer than the current one
> (arguably newer by at least 1/2*HZ sec)

That's only if we want to do no better than the current system. We'd want
a new variable called timer_margin or something, which would be dependent
on interrupt source and processor, and could be tuned up or down via
sysctl.

> When you finish running the timers at an interval and the new interval is
> significantly larger than the current one.

Make that larger or smaller. If we come out of a quiescent state (1 hz
interrupts, say) and start getting 10ms timers, we want to respond to them
right away.

> Remember each tick we poke the PIT anyway

We could also have a HZ_max tunable above which we would not try to
reprogram the interval. On older systems, this could be set at
100-200HZ...

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