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

[Steven Rostedt <rostedt@goodmis.org>]

On Thu, 20 Oct 2005, Ingo Molnar wrote:

>
> * john stultz <johnstul@us.ibm.com> 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.
>
> no, this is really a bad optimization that causes unrobustness.
> Correctness and robustness comes first. It is so easy to cause a
> 500-1000msec delay in the kernel, due to a bad driver or anything. The
> timekeeping code should not break like that.
>


FYI,

With rc4-rt13 and changing cycle_t to u64, my machine ran all night
without one backward step.  Since it use to show up after a couple of
hours, I would say that this is the fix.

John, Do you want me to take a crack at changing the periodic_hook into
using the ktimer code?  I understand Ingo's kernel much more than you, but
you definitely understand the timing code better than I.


Cheers,

-- Steve