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

[Alexander Graf]

On 09.09.2013, at 11:38, Benjamin Herrenschmidt wrote:

> 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...

We could probably quantify the drift through DEC. But I'm personally not too 
eager to worry about live migration on 970 :).


Alex