Re: pv clock: kvm is incompatible with xen :-(

[Jeremy Fitzhardinge <jeremy@goop.org>]

Gerd Hoffmann wrote:
> Wall clock is off a few hours though.  Oops.
>
> I think the way wall clock and system clock work together in xen (Jeremy
> correct me if I'm wrong) is that the wall clock specifies the point in
> time where the system clock started going.  As kvm fills in host system
> time into the guest system time fields the guest wall clock fields
> should be filled with the host boot time timestamp I'd say.
>   

Yes.  The wallclock field in the shared info structure is the wallclock 
time at boot; you compute the current time by adding the system 
timestamp to it.   System time changes are effected by retroactively 
changing the boot time of the machine, though that can also change 
because of suspend/resume/migrate.

In general the kernel only reads the wallclock time at boot, and then 
maintains it for itself from then on.  I think.

    J

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