Re: [Qemu-devel] [RFC PATCH] spapr: support time base offset migration

[Benjamin Herrenschmidt]

On Mon, 2013-09-09 at 11:32 +0200, Alexander Graf wrote:
> On 09.09.2013, at 11:29, Benjamin Herrenschmidt wrote:
> 
> > On Mon, 2013-09-09 at 08:06 +0200, Alexander Graf wrote:
> >> I think it's ok to restrict live migration to machines with the same
> >> tb frequency when kvm is enabled. Whether you implement it through a
> >> hardcoded 512Mhz or through a timebase value that gets live migrated
> >> and then compared is up to you - both ways work for me :).
> > 
> > The latter might be handy if we want to support migration on 970, though
> > we don't have the TBU40 stuff there so adjusting the TB in the host
> > kernel would be ... problematic.
> 
> Well, we could save/restore TB when we enter/exit the guest, no? 

Hard to do without introducing drift...

> But I really only want to have something that doesn't block the door for 
> someone who wants to enable things.
> 
> 
> Alex