Messages in this thread | | | Date | Thu, 20 Oct 2005 02:55:26 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: Ktimer / -rt9 (+custom) monotonic_clock going backwards. |
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On Wed, 19 Oct 2005, john stultz wrote: > > > > > > 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. > > Steven: What clocksource are you using? Could you send me your dmesg?
I have both a PIT/TSC and apic. So, as Thomas told me, the ktimer code should figure out what to use. So that's pretty much all I can say on clocksource ;)
As for the dmesg, there isn't really one. I have my own logging code that flagged this, as well as a check that would BUG on the system when this happened. So my messages may not mean much to you. I'm currently compiling Ingo's -rt12 (with a fix to his checking) to see if I can trigger it there too. My custom kernel doesn't touch the ktimer/timeofday code so I'm assuming that I can. But until I can trigger this on a kernel that I didn't taint, I'll stop bothering you :-)
> > > > > 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 ? > > Last night I just caught a bug I accidentally introduced with the fixed > interval math (oh, if only optimizations didn't dirty code so!), where > time inconsistencies were possible when clocksources were changed. I'm > not sure if that's the issue being seen above, but I'll wrap things up > and send out a B8 release today if I can. >
Hmm, I believe that the ktimers use the apic (when available) and let the jiffies still be calculated via PIT/TSC.
Thomas, is the above correct?
Would that have triggered your bug?
Thanks,
-- Steve
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