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On my host I am using libvirt and a KVM guest. When the host is shutting down, libvirt suspends the guest. When the host is starting up, libvirt resumes the guest. The problem is, if the guest is suspended and resumed after 24 hours for example, then the guest time is 24 hours in the past.

I thought that maybe the problem is with the clocksource, but it is set to "kvm-clock" already.

$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
kvm-clock tsc hpet acpi_pm 

$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource
kvm-clock
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kvm-clock syncs the guest time to host time on guest startup. You should use and ntp client in the guest, and shutdown/startup instead of using suspend/resume.

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Yes, I can confirm it syncs on startup, because when I do shutdown/startup of the guest everything is fine. Using ntp is not a solution for many reasons (it is a workaround, it panics when the time difference is huge, it requires access to time server). I am searching for a way to solve the problem with suspend/resume, because this is an interesting, nice and default option in libvirt. – Hristo Hristov Nov 25 '11 at 11:39
suspend is 1) migrate VM state to file and 2) destroy. When you resume from suspend, the VM state is restored (migrated from file back to VM memory). This state will include the current timestamp. So yes, it is default, but no, timing still matters, and the time has to come from somewhere, and this is where NTP should come in. I doubt another clock source will help but you can try with acpi_pm. – dyasny Nov 25 '11 at 14:19
You should not use NTP in the guest. – Brian Cain Nov 25 '11 at 22:55
@Brian Cain this is highly arguable, especially with no explanation or reasoning behind the statement. To provide a profflink: docs.redhat.com/docs/en-US/… – dyasny Nov 26 '11 at 11:08
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