Re: [PATCH v15 23/26] sched: early boot clock

From: Pavel Tatashin
Date: Mon Jan 07 2019 - 20:05:27 EST

I did exactly the same sequence on Kaby Lake CPU and could not
reproduce it. What is your host CPU?

Thank you,

On Mon, Jan 7, 2019 at 6:48 PM Dominique Martinet
<asmadeus@xxxxxxxxxxxxx> wrote:
> Pavel Tatashin wrote on Mon, Jan 07, 2019:
> > I could not reproduce the problem. Did you suspend to memory between
> > wake ups? Does this time jump happen every time, even if your laptop
> > sleeps for a minute?
> I'm not sure I understand "suspend to memory between the wake ups".
> The full sequence is:
> - start a VM (just in case, I let it boot till the end)
> - suspend to memory (aka systemctl suspend) the host
> - after resuming the host, soft reboot the VM (login through
> serial/ssh/whatever and reboot or in the qemu console 'system_reset')
> I've just slept exactly one minute and reproduced again with the fedora
> stock kernel now (4.19.13-300.fc29.x86_64) in the VM.
> Interestingly I'm not getting the same offset between multiple reboots
> now despite not suspending again; but if I don't suspend I cannot seem
> to get it to give an offset at all (only tried for a few minutes; this
> might not be true) ; OTOH I pushed my luck further and even with a five
> seconds sleep I'm getting a noticeable offset on first VM reboot after
> resume:
> [ 0.000000] Hypervisor detected: KVM
> [ 0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
> [ 179.362163] kvm-clock: cpu 0, msr 13c01001, primary cpu clock
> [ 179.362163] clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
> Honestly not sure what more information I could give, I'll try on some
> other hardware than my laptop (if I can get a server to resume after
> suspend through ipmi or wake on lan); but I don't have anything I could
> install ubuntu on to try their qemu's version... although I really don't
> want to believe that's the difference...
> Thanks,
> --
> Dominique