Monotonic clock with KVM pv-clock

[Nadav Har'El <nyh@math.technion.ac.il>]

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             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |Diplomat: A man who always remembers a
http://nadav.harel.org.il           |woman's birthday but never her age.