Messages in this thread | | | Date | Mon, 30 Jul 2018 21:49:48 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH RESEND 1/1] x86: tsc: avoid system instability in hibernation |
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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
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