Re: [Qemu-devel] Rethinking missed tick catchup

[Eric Blake]

On 09/13/2012 08:34 AM, Avi Kivity wrote:
> On 09/13/2012 05:22 PM, Gleb Natapov wrote:
>>>
>>> It's much easier for us to call into qemu-ga to do the time correction
>>> whenever this event occurs than to try and have libvirt figure out when
>>> it's necessary.
> 
>> And if guest does not have qemu-ga what is better inject interrupts like
>> crazy for next 2 minutes or leave guest with incorrect time?
> 
> We can try to S3 and resume the guest.  The guest will assume that it
> has slept for an unknown amount of time and resync from the RTC.

Just restating to make sure I'm clear: you are proposing that after host
suspend and host wakeup, _then_ qemu asks the guest to go into S3
followed by an immediate resume.  During the time that the guest goes
into S3, its clock is way off; but then the immediate resume will be the
necessary kick to the guest to resync, and at that point, the guest can
assume that it has been off since the host originally suspended (rather
than the instant window where qemu actually bounced S3 after the host
had already resumed).

> This may not work for really old server oriented guests.

S3 requires guest cooperation, period.  But so does qemu-ga.  It's
better than nothing, and we can't get perfection without guest cooperation.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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