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

[Steven Rostedt <rostedt@goodmis.org>]

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?

-- Steve