[Users] TSC clocksource gets lost after live migration

[Markus Stockhausen]

Hello,

we have an up to date ovirt 3.4 installation. Inside we are running SLES11 SP3
VMs (Kernel 3.0.76-0.11). After live migration of these VMs they all of a sudden
do not react any longer and CPU usage of the VM goes to 100%.

We identified kvm-clock source to be the culprit and therefore switched to another
clocksource. We ended with hpet but are not happy with that as our inital goal
was to use the more simple designed TSC clocksoure.

The reason behind that is the question I have for you experts.

Our hosts all have the constant_tsc CPU flag available. Just to mention these
are not identical hosts. We have a mix of Xeon 5500 and 5600 machines. E.G.
[root at colovn01 ~]# cat /proc/cpuinfo | grep constant_tsc | wc -l
8

When we start the VM the client sees TSC as available clocksource:

colvm53:~ # cat /sys/devices/system/clocksource/clocksource0/available_clocksource
kvm-clock tsc hpet acpi_pm

After the first live migration to another host that also has constant_tsc (see above)
that flag is lost inside the VM.

colvm53:~ # cat /sys/devices/system/clocksource/clocksource0/available_clocksource
kvm-clock hpet acpi_pm

Any ideas?

Markus


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