Re: [qemu-s390x] [PATCH v1] s390x/tod: properly stop the KVM TOD while the guest is not running

[Christian Borntraeger]

On 27.11.2018 14:06, Thomas Huth wrote:
> On 2018-11-27 13:43, Christian Borntraeger wrote:
>> On 27.11.2018 12:41, David Hildenbrand wrote:
>>> Just like on other architectures, we should stop the clock while the guest
>>> is not running. This is already properly done for TCG. Right now, doing an
>>> offline migration (stop, migrate, cont) can easily trigger stalls in the
>>> guest.
>>>
>>> Even doing a
>>>     (hmp) stop
>>>     ... wait 2 minutes ...
>>>     (hmp) cont
>>> will already trigger stalls.
>>>
>>> So whenever the guest stops, backup the KVM TOD. When continuning to run
>>> the guest, restore the KVM TOD.
>>
>> We do a similar thing for managedsave so it probably makes sense to solve
>> the stall warnings. Now: At the same time, we actually want to have the guest
>> see the real time and maybe even share the TOD clock with the host in some
>> way, while at the same time avoid the stall warnings.
> 
> Hmm, by the way, do we also have to consider the "-rtc clock=host|rt|vm"
> option from the commandl line, or is this an orthogonal concept?

I think this option does not work at all in how time works on s390.