Re: [Qemu-devel] Rethinking missed tick catchup

[Anthony Liguori]

Avi Kivity <address@hidden> writes:

> On 09/13/2012 05:42 PM, Eric Blake wrote:
>> 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).
>
> Correct.  In theory we can shut down networking while this is happening
> so the guest can't tell it's in a time machine.
>
>> 
>>> 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.
>
> qemu-ga requires either an admin/tool to install qemu-ga, or for qemu-ga
> to be preinstalled by the OS vendor.  S3 requires S3 support to be
> provided by the host vendor, and for it to be functional.  A
> significantly easier bar to clear.

We can easily generate an ISO that includes a pre-built version of
qemu-ga.

Plus, there's a whole variety of other features enabled once we can
assume qemu-ga is available.  It's worth solving that problem.

Regards,

Anthony Liguori

>
>
> -- 
> error compiling committee.c: too many arguments to function