On Mon, 30 Jul 2018, Eduardo Valentin wrote:
> On Mon, Jul 30, 2018 at 10:53:54AM +0200, Peter Zijlstra wrote:
> > On Thu, Jul 26, 2018 at 08:56:56AM -0700, Eduardo Valentin wrote:
> > > System instability are seen during resume from hibernation when system
> > > is under heavy CPU load. This is due to the lack of update of sched
> > > clock data
> >
> > Which would suggest you're already running with unstable sched clock.
> > Otherwise nobody would care about the scd stuff.
>
> Yes.
I doubt that...
> >
> > What kind of machine are you running? What does:
> >
> > dmesg | grep -i tsc
> >
> > say?
>
> Here:
> [ 0.000000] tsc: Fast TSC calibration using PIT
> [ 0.004005] tsc: Detected 3000.000 MHz processor
> [ 0.066796] TSC deadline timer enabled
> [ 3.904269] clocksource: tsc: mask: 0xffffffffffffffff max_cycles:
> 0x2b3e459bf4c, max_idle_ns: 440795289890 ns
>
... because if the sched clock would be unstable then you'd have something
like 'TSC unstable' in dmesg, which you obviously do not.
'sched_clock: Marking unstable' is the other message which would be
emitted.
> > > The fix for this situation is to mark the sched clock as unstable
> > > as early as possible in the resume path, leaving it unstable
> > > for the duration of the resume process. This will force the
> > > scheduler to attempt to align the sched clock across CPUs using
> > > the delta with time of day, updating sched clock data. In a post
> > > hibernation event, we can then mark the sched clock as stable
> > > again, avoiding unnecessary syncs with time of day on systems
> > > in which TSC is reliable.
> >
> > None of this makes any sense. Either you were already unstable and it
> > should already have worked and them marking it stable is an outright
> > bug, or your sched clock was stable but then your initial diagnosis of
> > lack of scd updates is complete garbage.
> >
>
> I see, or it is just a workaround for the underling issue. I, for sure, see no
> lockups anymore after forcing the scd updates. The other thing which are not
> super clear is that this happens during the unfreezing of tasks. If I get a
> set of cpu hog tasks while unfreezing, I see the system throwing worqueue
> lockup
> detectors in hibernation restore.
Yes, it pretty much papers over something else. Can you please provide a
full dmesg from boot to failure case?
Another question: Does the system recover after issuing the lockup messages
or is it hosed completely?
Thanks,
tglx
