One-shot-oriented event timers management

[Gary Jennejohn]

On Mon, 30 Aug 2010 13:07:38 +0300
Alexander Motin <mav at FreeBSD.org> wrote:

> Gary Jennejohn wrote:
> > Hmm.  I applied your patches and am now running the new kernel.  But I
> > only installed the new kernel and didn't do make buildworld installworld.
> > 
> > Mu systat -vm 1 doesn't look anything like yours.  I'm seeing about 2300
> > interrupts per second and most of those are coming from the hpet timers:
> > 
> > 1122 hpet0:t0
> > 1124 hpet0:t1
> 
> It means 1000Hz of hardclock (hz) events mixed with 127Hz of statclock
> (stathz) events. HPET timer here works in one-shot mode handling it.
> 
> > So, what else did you do to reduce interrupts so much?
> > 
> > Ah, I think I see it now.  My desktop has only C1 enabled.  Is that it?
> > Unfortunately, it appears that only C1 is supported :(
> 
> Yes, as I have said, at this moment empty ticks skipped only while CPU
> is in C2/C3 states. In C1 state there is no way to handle lost events on
> wake up. While it may be not very dangerous, it is not very good.
> 

Too bad.  I'd say that systems which are limited to C1 don't benefit
much (or not at all) from your changes.

--
Gary Jennejohn