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So I have this VM (I don't have access to the host system) running Debian Lenny, with the following kernel: 2.6.32-bpo.5-686 #1 SMP

This morning I upgraded the VM to Squeeze (finally), and as the system rebooted, I noticed that it was painfully slow. The dist-upgrade (after reboot) is still running, and has been for several hours. However, the load is below 1, CPU usage around 50%, no big disk activity, and there is plenty of RAM available. I don't understand where this performance problem (it's really, REALLY slow) come from. The odd thing though, is that the clock seems to be very slow as well: the seems to believe that only a few minutes have passed since it has been rebooted, even though it's actually been hours.

Has anyone experienced a similar problem? Or do you have suggestions about where to look for clues?

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Ok, so I found what the problem was. As it turns out it wasn't a Xen VM, but anyway. Apparently the VM did pick the wrong clocksource (kvm-clock instead of acpi). Changing it in /sys/devices/system/clocksource/clocksource0/current_clocksource immediately solved the problem. According to the owner of the host system, it's a problem he has seen a few times before (seemingly randomly, he hasn't yet been able to pinpoint where the bug lies exactly), and is unrelated to the upgrade I was performing.

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If KVM is similar to XEN there should be a clocksource-directive in the KVM configuration for your VM. These can differ from OS to OS. –  Nils May 22 '12 at 20:27

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