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

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

On Thu, 2005-10-20 at 06:05 -0400, Steven Rostedt wrote:
> 
> On Thu, 20 Oct 2005, Steven Rostedt wrote:
> 
> > >
> > > Not anymore.
> > >
> > > include/linux/time.h:
> > >
> > > /* timeofday base types */
> > > typedef s64 nsec_t;
> > > typedef unsigned long cycle_t;
> > >
> >
> > FYI,
> >
> > I just switched cycle_t to u64 and hackbench no longer makes the time go
> > backwards.
> >
> > 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)? 

thanks
-john

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