[Users] TSC clocksource gets lost after live migration

[Darrell Budic]

I see this on some guests as well, possibly relating to moving between hosts with the same family of CPU but different absolute CPU speeds?

  -Darrell

On Apr 4, 2014, at 8:33 AM, Michal Skrivanek <michal.skrivanek at redhat.com> wrote:

> Hi,
> this is more for the KVM folks I suppose…can you get the qemu process cmdline please?
> 
> Thanks,
> michal
> 
> On 3 Apr 2014, at 12:13, Markus Stockhausen wrote:
> 
>> 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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