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

On Wed, 19 Oct 2005, Thomas Gleixner wrote:

> On Wed, 2005-10-19 at 10:59 -0400, Steven Rostedt wrote:
> > Hi Thomas,
> >
> > I switched my custom kernel timer to use the ktimers with the prio of -1
> > as you mentioned to me offline. I set up the timer to be monotonic and
> > have a requirement that the returned time is always greater or equal to
> > the last time returned from do_get_ktime_mono.
> >
> > Now here's the results that I got between two calls of do_get_ktime_mono
> >
> > 358.069795728 secs then later 355.981483177. Should this ever happen?
>
> Definitely not. monotonic time must go forwards.
>
> > I haven't look to see if this happens in vanilla -rt10 but I haven't
> > touched your ktimer code except for my logging and the patch with the
> > unlock_ktimer_base (since I was based off of -rt9)
>
> The ktimer code itself calls the timeofday code, which provides the
> monotonic clock. I have no idea what might go wrong.
>
> Is this reproducible ?
>

FYI, I just merged my changes with -rt13 and everything seems to be
working very smoothly. I've been running my kernel over an hour without
showing the backward times. I haven't even added the change from cycle_t
to be 64 bits.


So, knock on wood, maybe one of the latest updates fixed the problem. Or
maybe as soon as I hit send, the machine will crash.

I'll keep you all posted.

-- Steve

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