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Re: [qemu-s390x] [PATCH v1] s390x/tod: properly stop the KVM TOD while t

From: Thomas Huth
Subject: Re: [qemu-s390x] [PATCH v1] s390x/tod: properly stop the KVM TOD while the guest is not running
Date: Tue, 27 Nov 2018 14:06:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

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?


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