Re: [Bug #14859] System timer firing too much without cause

Rafael J. Wysocki
2010-01-25T20:59:33Z

On Monday 25 January 2010, Shawn Starr wrote:
> On Monday 25 January 2010 12:20:38 Thomas Gleixner wrote:
> > On Mon, 25 Jan 2010, Shawn Starr wrote:
> > > On Monday 25 January 2010 05:35:50 Thomas Gleixner wrote:
> > > > Shawn, why can't you use dynamic ticks ? In the bugzilla I just see
> > > > that you worry about the IRQ0 interrupts (which are correct and
> > > > necessary when the system is in nohz mode) and the extra rescheduling
> > > > interrupts. How is the system misbehaving ?
> > >
> > > Well, this all stems from trying to use Radeon KMS with IRQs
> > > on. Doing so I see system stalls and this is quite noticeable
> > > however, I am able to show this same stall on the quad core with the
> >
> > x> same GPU. Right now, it is unclear to me if there is a underlying
> >
> > > irq issue or a bug in the radeon driver code that is showing these
> > > stalls. Since the radeon folks - at the moment - do not think it is
> > > a coding problem in their driver
> >
> > Does the stall go away, when you disable dynticks ?
> >
>
> It does not, no.
>
> > > My impression was using dynamic ticks meant ticks were on demand and
> >
> > Dynamic ticks are providing a continuous tick long as the machine is
> > busy. When a core becomes idle, we programm the timer to go off at the
> > next scheduled timer event, if the event is longer away than the next
> > tick. When the core goes out of idle (due to the timer or some other
> > event) we restart the tick.
> >
> > So you see less timer interrupts (IRQ0 + Local timer interrupts)
>
> With dynamic ticks on or off, LOC increments rapidly, but I assume that is
> normal behavour.
>
> So if none of this really is a kernel issue, I defer it to the radeon folks to
> comment further.
>
> Please remove from regression list, I'll close the original bug.

OK, closing it right now.

Rafael