Re: [Qemu-devel] Relative/Absolute timing snapshot problem

[Blue Swirl <blauwirbel@gmail.com>]

On Mon, Mar 28, 2011 at 7:32 PM, Jes Sorensen <Jes.Sorensen@redhat.com> wrote:
> On 03/28/11 18:25, Clemens Kolbitsch wrote:
>>> Hi Clemens,
>>> >
>>> > Could you clarify what you are doing, when you say snapshot do you mean
>>> > a savevm operation (ie. checkpoint) or a disk snapshot?
>> I Jes,
>>
>> sorry for not being clear: I use a savevm operation.
>>
>> Following setup: I have a base file (qcow2 or qew format) and a snapshot file
>> (generated via 'qemu-img create -b <basefile> -f qcow2 <snapshotfile>') and
>> boot the snapshot file. Once the system (WinXP SP3 guest) has fully started, I
>> create a snapshot (savevm <foo>) and exit the emulator. Later, I resume the
>> snapshot by starting Qemu with the snapshotfile and say 'loadvm <foo>'.
>>
>> Actually, I found that the times I gave in my last email were way
>> underestimated. The time difference is MUCH larger than 2-3 seconds per day. A
>> week-old snapshot can take minutes to load on a reasonably idle host machine.
>
> Ok, then I am pretty much in the dark on this one - I don't know
> anything about the checkpoint/restart feature and the impact on things
> like the clock. I only worked on the live snapshot code (for disk
> snapshots).
>
> Hopefully someone else will have an idea.

Sounds like a bug in the RTC. Maybe decoalescing is triggered, which
would cause a burst of RTC interrupts to catch with the system clock?