XP Guest Clock Slow

Hello,

I just upgraded my hardware to a VT-capable CPU, and am getting up-to-speed with kvm.

The clock on my XP guest significantly lags (e.g. by 50%) behind the host. I lose several hours overnight in the guest clock. (Not just a few seconds) System load seems to aggravate the problem.

I have seen similar behavior in quick tests on a Vista client. My Ubuntu client is fine, presumably due to clocksource==kvm-clock in guest.

Everything else works fine in all guest VMs. (Amazingly well, actually) Performance is equal to or better what I have been used to with VMware Server.

Host CPU is Athlon 64 X2 with SB700 chipset.
System dumps (lspci, cpuinfo, etc) available on request (I don't want to flood)

Host environment is Debian Lenny, with the distribution 2.6.26 kernel. Currently running a locally compiled/installed kvm-82
I also saw the same issue with the kvm-72 Debian package.

My host clock is set to 'hpet'

| /sys/devices/system/clocksource/clocksource0$ cat *
| hpet acpi_pm jiffies tsc
| hpet

Is there a paravirtual clock driver for M$ clients available? What is current best practice to work around this problem?

Thanks,

--
Marty

Update in case someone else fights the same issue.

Replaced Lenny kernel with 2.6.28 kernel.org compile. All is well now - At least within a few seconds per day.

--
Marty

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of [email protected]
Sent: Friday, January 16, 2009 10:15 AM
To: [email protected]
Subject: XP Guest Clock Slow

Hello,

I just upgraded my hardware to a VT-capable CPU, and am getting up-to-speed with kvm.

The clock on my XP guest significantly lags (e.g. by 50%) behind the host. I lose several hours overnight in the guest clock. (Not just a few seconds) System load seems to aggravate the problem.

I have seen similar behavior in quick tests on a Vista client. My Ubuntu client is fine, presumably due to clocksource==kvm-clock in guest.

Everything else works fine in all guest VMs. (Amazingly well, actually) Performance is equal to or better what I have been used to with VMware Server.

Host CPU is Athlon 64 X2 with SB700 chipset.
System dumps (lspci, cpuinfo, etc) available on request (I don't want to flood)

Host environment is Debian Lenny, with the distribution 2.6.26 kernel. Currently running a locally compiled/installed kvm-82
I also saw the same issue with the kvm-72 Debian package.

My host clock is set to 'hpet'

| /sys/devices/system/clocksource/clocksource0$ cat *
| hpet acpi_pm jiffies tsc
| hpet

Is there a paravirtual clock driver for M$ clients available? What is current best practice to work around this problem?

Thanks,

--
Marty

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As in Windows XP and earlier, you can configure the NTP client via the control panel. My host runs a ntp server and all guest are configured to synchronize very often.

- Florent

The implication there, is that KVM does not have a working clock for Windows guests?

I have no problem here, the guests' (XP, 2003, 2008, Vista, 7...) clocks are almost as accurate as host's one.

The facts you are describing are close to the behavior of Windows clock while it is being synchronized. Depending on the sign of the difference between local clock and reference clock, Windows slows down/speeds up its clock by 2.

You could have a look at system messages, it can be invoked by a right click on "My Computer" -> "Manage". Time service used to output some message during the synchro.

- Florent