Re: [Qemu-devel] Missing guest clock-sync on Host clock change

[Erik Rull <erik.rull@rdsoftware.de>]

Laszlo Ersek wrote:
> On 03/27/14 09:41, Erik Rull wrote:
>> Hi all,
>>
>> I would like to have the guest "drifting" to a new set clock on the host.
>>
>> My problem is the following:
>>
>> - Host System (Linux) starts up, hwclock and kernel time are synced,
>> guest starts up with -rtc clock=host,driftfix=slew (which I assume
>> should fix any drift issue on ACPI compatible guest OSes)
>> - Host System kernel time drifts against the hwclock (jiffies timer due
>> to no other available useful timer on SMP systems - core2duo has no hpet!)
>> - calling "hwclock -s" on the host resyncs the kernel time with the
>> hwclock, so "date" and "hwclock" show the same again
>> - the guest stays at the "old" kernel time before the sync - also after
>> 1 hour the delta is still the same, so no sync or slew is done :-(
>>
>> My guest OS is Windows 8, which must have ACPI enabled, otherwise it
>> will not work.
>>
>> Any ideas how to proceed? Maybe some command line parameters are wrong?
>>
>> I need this resync for the guest due to external synchronization - it
>> must not be millisecond-precise, but a 9 seconds shift during a run
>> overnight is too much!
>
> My take: the hardware clock (the RTC) in the guest has correct value,
> but the guest OS system time os not refreshed from it. Install the guest
> agent in Windows, and call its "guest-set-time" command (with virsh
> qemu-agent-command, or otherwise). Do not pass any argument for the
> optional "time" parameter; this way the guest will sync its kernel time
> from its RTC.
>
> See:
> - qga/qapi-schema.json, "guest-set-time",
> - qga/commands-win32.c, qmp_guest_set_time()
>
> In any case this is just a guess.
>
> Laszlo
>

Hi Laszlo,

thanks, I will try that, but might take some time, because the changes for 
the qemu-ga are bigger to activate. Is there a possiblity to set the RTC of 
the guest automatically in sync with the host hardware RTC? I didn't find a 
parameter for that.

Best regards,

Erik