On Thu, 21 May 2015 21:41:23 -0300 Marcelo Tosatti <mtosatti@xxxxxxxxxx> wrote: > On Mon, May 18, 2015 at 10:13:03PM -0400, Sasha Levin wrote: > > On 05/18/2015 10:02 PM, Sasha Levin wrote: > > > On 05/18/2015 08:13 PM, Marcelo Tosatti wrote: > > >> GOn Mon, May 18, 2015 at 07:45:41PM -0400, Sasha Levin wrote: > > >>>> On 05/18/2015 06:39 PM, Marcelo Tosatti wrote: > > >>>>>> On Tue, May 12, 2015 at 07:17:24PM -0400, Sasha Levin wrote: > > >>>>>>>> Hi all, > > >>>>>>>> > > >>>>>>>> I'm seeing odd jump in time values during boot of a KVM guest: > > >>>>>>>> > > >>>>>>>> [...] > > >>>>>>>> [ 0.000000] tsc: Detected 2260.998 MHz processor > > >>>>>>>> [3376355.247558] Calibrating delay loop (skipped) preset value.. > > >>>>>>>> [...] > > >>>>>>>> > > >>>>>>>> I've bisected it to: > > >>>>>> > > >>>>>> Paolo, Sasha, > > >>>>>> > > >>>>>> Although this might seem undesirable, there is no requirement > > >>>>>> for sched_clock to initialize at 0: > > >>>>>> > > >>>>>> " > > >>>>>> * > > >>>>>> * There is no strict promise about the base, although it tends to start > > >>>>>> * at 0 on boot (but people really shouldn't rely on that). > > >>>>>> * > > >>>>>> " > > >>>>>> > > >>>>>> Sasha, are you seeing any problem other than the apparent time jump? > > >>>> > > >>>> Nope, but I've looked at it again and it seems that it jumps to the host's > > >>>> clock (that is, in the example above the 3376355 value was the host's clock > > >>>> value). > > >>>> > > >>>> > > >>>> Thanks, > > >>>> Sasha > > >> Sasha, thats right. Its the host monotonic clock. > > > > > > It's worth figuring out if (what) userspace breaks on that. I know it says that > > > you shouldn't rely on that, but I'd happily place a bet on at least one userspace > > > treating it as "seconds since boot" or something similar. > > > > Didn't need to go far... In the guest: > > > > # date > > Tue May 19 02:11:46 UTC 2015 > > # echo hi > /dev/kmsg > > [3907533.080112] hi > > # dmesg -T > > [Fri Jul 3 07:33:41 2015] hi > > Sasha, > > Can you give the suggested patch (hypervisor patch...) a try please? > (with a patched guest, obviously). > > KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system > MSR I've tried your v2, it works for me. My test-case is very simple though: I just boot a VM, log in and reboot. This reproduces the issue Sasha reported 100% of the times for me (don't need multi-vcpu guest either). Would be nice to hear from Sasha too. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
