Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards.

[john stultz <johnstul@us.ibm.com>]

On Thu, 2005-10-20 at 12:58 -0400, Steven Rostedt wrote:
> On Thu, 20 Oct 2005, john stultz wrote:
> 
> > > >
> > > > John, would this cause any problems to keep cycle_t at s64?
> > >
> > > I mean at u64.
> >
> > Performance would be the only concern. It had been a u64 before I
> > started optimizing the code a bit.
> >
> > The real problem however was the timeofday_perioidic_hook() was being
> > starved. Since not all clocksources are 64 bits wide (although most do
> > not overflow as fast as 32bits of the TSC) I'm not sure that will always
> > solve the issue.
> >
> > Ingo: Should the periodic_hook() call be converted to using the ktimer
> > or some other interface to ensure that it will be regularly run at some
> > frequency (currently 50ms, but that can be changed)?
> >
> 
> Thomas showed me a trick with the ktimers API, that I use to schedule my
> custom scheduler.  If you set periodic_hook to be called via ktimer with a
> prio of -1, it will force the timer to be run in the timer interrupt
> instead of a softirq task.
> 
> Now the issue is the latency this would cause and to make sure that
> periodic_hook only grabs raw locks. Ingo?


Ok, do let me know if its a problem spot. I've not been too thoughtful
in minimizing how long the lock is held for. I'll see if that cannot be
minimized.

Thanks for the thorough testing and feedback!
-john

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