Re: One-shot-oriented event timers management

On Wed, 01 Sep 2010 13:44:26 +0300
Alexander Motin <mav_at_FreeBSD.org> wrote:

> Alexander Motin wrote:
> > Gary Jennejohn wrote:
> >> On Mon, 30 Aug 2010 12:11:48 +0200
> >> OK, this is purely anecdotal, but I'll report it anyway.
> >>
> >> I was running pretty much all day with the patched kernel and things
> >> seemed to be working quite well.
> >>
> >> Then, after about 7 hours, everything just stopped.
> >>
> >> I had gkrellm running and noticed that it updated only when I moved the
> >> mouse.
> >>
> >> This behavior leads me to suspect that the timer interrupts had stopped
> >> working and the mouse interrupts were causing processes to get scheduled.
> >>
> >> Unfortunately, I wasn't able to get a dump and had to hit reset to
> >> recover.
> >>
> >> As I wrote above, this is only anecdotal, but I've never seen anything
> >> like this before applying the patches.
> > 
> > One-shot timers have one weak side: if for some reason timer interrupt
> > getting lost -- there will be nobody to reload the timer. Such cases
> > probably will require special attention. Same funny situation with
> > mouse-driven scheduler happens also if LAPIC timer dies when pre-Core-iX
> > CPU goes to C3 state.
> 
> I have reproduced the problem locally. It happens more often when ticks
> are not stopped on idle, like in your original case (or if explicitly
> enabled by kern.eventtimer.idletick sysctl).
> 
> I've made some changes to HPET driver, which, I hope, should fix
> interrupt losses there.
> 
> Updated patch: http://people.freebsd.org/~mav/timers_oneshot6.patch
> 
> Patch also includes some optimizations to reduce lock contention.
> 
> Thanks for testing.
> 

OK, I'll give it a try, althought your previous patch seems to be working
quite well.

BTW I've also been using tm6292_idle.patch.  Do I really need it?

--
Gary Jennejohn