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 Thanks, Sasha -- 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
