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 -- 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
