Monotonic clock with KVM pv-clock

Nadav Har'El
2014-01-20T10:07:05Z

Hi,

I'm trying to figure out how a guest OS can get a monotonic clock using
KVM's paravirtual clock.

At first, I thought that the clock I get using KVM_SYSTEM_TIME is a
monotonic clock, based on the host's monotonic clock.
But I'm no longer sure this is actually done correctly:

1. What happens on live migration? On the new host, will the
KVM_SYSTEM_TIME continue from the same point? Or will it jump because
KVM_WALL_CLOCK (the wall time during boot) is different on the new host?

2. What happens when the wall-clock time is set on the host? I was
hoping that only KVM_WALL_CLOCK changes and KVM_SYSTEM_TIME doesn't,
but am no longer sure this is actually the case.

If KVM_SYSTEM_TIME is not a correct way to get a monotonic paravirtual clock
from KVM, is there a correct way?

Thanks,
Nadav.

--
Nadav Har'El | Monday, Jan 20 2014, 19 Shevat 5774
nyh@math.technion.ac.il |-----------------------------------------
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