Writing up my findings so far: - this looks to be a m1.small instance (1 vcpu, 1.7GB memory) - this instance type is a PV guest
So sched_clock (which is used by printk) will be using paravirt_sched_clock which is set to xen_clocksource_read. The time info is kept in a per-cpu variable (vcpu_info). This is initially part of the hypervisor shared info but get changed later. start_kernel() ... setup_per_cpu_areas(); /* printks from above are ok */ smp_prepare_boot_cpu(); xen_smp_prepare_boot_cpu(); xen_setup_vcpu_info_placement(); /* vcpu_info changed */ xen_init_spinlocks(); /* printks from above call jumped in time */ So it looks like for some yet unknown reason, registering the vcpu_info with the hypervisor is messing up the clocktime data. @Joe, was this always happening (with the same instance type maybe) or about how often. I am trying to get a feeling for whether it is some race or maybe related to xen hypervisor version. Also will try to play around with this on a local Xen host (but rather tomorrow). -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1349883 Title: dmesg time wildly incorrect on paravirtual EC2 instances. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1349883/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs