Clocksource tsc unstable (delta = -4398046474878 ns)

[Sebastian Hetze <s.hetze@linux-ag.com>]

Hi *,

this message appeared in the KVM guest kern.log last night:

Mar 27 22:35:30 guest kernel: [260041.559462] Clocksource tsc unstable (delta = -4398046474878 ns)

The guest is running a 2.6.31-20-generic-pae ubuntu kernel with
hrtimer-tune-hrtimer_interrupt-hang-logic.patch applied.

If I understand things correct, in kernel/time/clocksource.c
clocksource_watchdog() checks all the
/sys/devices/system/clocksource/clocksource0/available_clocksource
every 0.5sec for an delta of more than 0.0625s. So the tsc must have
changed more than one hour within two subsequent calls of
clocksource_watchdog. No event in the host nor anything in the
guest gives reasonable cause for this step.

However, the number 4398046474878 is only 36226 ns away from
4*1024*1024*1024*1024

The guest is an 32 bit system running in a 64 bit host. Is this an
possible cause of this strange message? Any other idea what is going
wrong here? Maybe this is a hardware bug?

Best regards,

  Sebastian