Re: [Qemu-devel] [PATCH 1/1] virtio-balloon: reset the statistic timer to load device

["Denis V. Lunev" <den@openvz.org>]

On 03/29/2016 05:07 PM, Michael S. Tsirkin wrote:
> On Tue, Mar 29, 2016 at 05:00:49PM +0300, Denis V. Lunev wrote:
>> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
>>
>> If before loading snapshot we had set the timer of statistics, then after
>> applying snapshot the expiry time would be irrelevant for the restored
>> state of the virtual clocks. A simple fix is just to restart the timer
>> after loading snapshot.
>>
>> For the user it may look like a long delay of statistics update after switch
>> to the snapshot.
>>
>> Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
>> Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
>> Signed-off-by: Denis V. Lunev <den@openvz.org>
>> CC: Michael S. Tsirkin <mst@redhat.com>
> I'm inclined to think we really should migrate the timer,
> otherwise user might wait twice as long as expected ...
this is not a big deal. This timer is a part of the QEMU state,
which was configured for this exact running instance, not
for the guest. Moreover, we have switched to new guest state
which can be on the different CPU with different timings etc
and thus we should let the guest to run for some time.

In the perfect world you should not save the time to the migration
state but save the time at reset callback and restore it here at
postload, but this seems over engineering.

Statistics delivery is "best effort", nobody will die if one
shot will be missed.