Re: [Xen-devel] HVM Migration of domU on Qemu-upstream DM causes stuck system clock with ACPI

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 03/06/13 18:18, Alex Bligh wrote:
> George,
>
> --On 3 June 2013 18:12:47 +0100 George Dunlap 
> <george.dunlap@xxxxxxxxxxxxx> wrote:
> > > Will this work with all guests? We (unfortunately) do not know whether
> > > the
> > > guest is Linux with or without PV, Windows with or without PV or 
> > > what. I
> > > /think/ this is going to give problems when the guest is not using
> > > the PV timer (including Windows). Is that right?
> > >
> > > I'd be happiest if it selected native_paravirt whenever the guest was
> > > using the PV timer, but not otherwise. Happy to test patches for that.
> > I'm not sure the effect, but I suspect it probably won't work quite
> > right.  Might be worth a quick test.
> >
> > We do want to fix this properly (which means, "just works w/o having to
> > use a work-around"); I'm trying to understand the exact nature of the
> > error now.
> Sorry did you mean using native_paravirt on Linux guests with PV support
> wouldn't work quite right, or using that on all guests wouldn't work 
> quite
> right, or that switching automatically if use of the PV timer was
> detected wouldn't work quite right?
I mean that if you enable it for guests that aren't using a PV 
clocksource (e.g., Windows guests), I'm not sure what will happen. It 
might be fine, but you should  probably test it. :-)
Switching TSC modes isn't the right thing to do -- the right thing is to 
figure out where the math is getting messed up and make it work properly 
no matter which mode you're in.
 -George




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