Re: [Qemu-devel] [PATCH v5 07/16] apic: Open-code timer save/restore

[Anthony Liguori]

On 12/19/2011 06:34 PM, Jan Kiszka wrote:
> On 2011-12-20 01:31, Anthony Liguori wrote:
> > On 12/19/2011 05:45 PM, Jan Kiszka wrote:
> > > On 2011-12-19 23:21, Anthony Liguori wrote:
> > > > On 12/15/2011 06:33 AM, Jan Kiszka wrote:
> > > > > To enable migration between accelerated and non-accelerated APIC
> > > > > models,
> > > > > we will need to handle the timer saving and restoring specially and can
> > > > > no longer rely on the automatics of VMSTATE_TIMER. Specifically,
> > > > > accelerated model will not start any QEMUTimer.
> > > > >
> > > > > This patch therefore factors out the generic bits into apic_next_timer
> > > > > and introduces a post-load callback that can be implemented differently
> > > > > by both models.
> > > > >
> > > > > Signed-off-by: Jan Kiszka<address@hidden>
> > > >
> > > > So you basically want the timer to be a dummy field for the in-kernel
> > > > apic?
> > > >
> > > > Can you fix this up in a pre-save routine (put QEMUTimer into a state
> > > > where there isn't an event pending)?
> > >
> > > It is not a dummy field, it contains the proper state in both cases. We
> > > just need to convert it to an open-coded state to avoid the QEMUTimer
> > > restoration magic in the in-kernel case (where there must be no
> > > QEMUTimer).
> >
> > So the state gets fed into the kernel instead of userspace?
>
> Nope. It's kept for eventual use by a user space model.

I think you misunderstood my comments.

When you are using the in-kernel APIC, the is no implementation for the 
post_load hook.  As far as I can tell, the state isn't used.

I know it's used by the user space model but from what I can tell, the value is 
essentially sync with the in-kernel APIC almost immediately as it happens during 
KVM_RUN.

So it's a QEMUTimer in the userspace model, but it's just an integer when used 
in the in-kernel APIC as the timer never fires.  It is just saved/restored from 
and to the kernel.

Is this correct?

Regards,

Anthony Liguori