[CentOS-virt] Is kvm-clock dependant on hardware of Physical Server?

Steven Ellis mail_lists at stevencherie.net
Thu Nov 4 00:25:47 EDT 2010

On Thu, 04 Nov 2010 17:03:33 +1300, Steven Ellis
<mail_lists at stevencherie.net> wrote:
> I've got a three Centos 5.5 KVM severs, but only one of them is
> guests with the kvm-clock source.
> The two servers I'm not seeing kvm-clock on have Athlon x2 64bit
> processors.
> The other server with kvm-clock has a Phenom II X6 1090T Processor.
> I've checked the system configuration and all the boxes have the same set
> of RPM packages. To confirm that the issue was physical
> hardware specific I migrated a VM from the Athlon to the Phenom server
> the kvm-clock source appeared.
> Any ideas why I'm not seeing kvm-clock with my Athlon X2 processors, or
> there another difference I haven't caught?

Well it looks like the issue relates to constant_tsc.

Out of the 3 boxes only the Phenom has constant_tsc in the CPU flags. There
appears to be some kernel list references here -
* http://www.mail-archive.com/kvm@vger.kernel.org/msg10193.html

This finally led to the following docs

Looks like I need to do some tweaking at the grub level for my Athlon X2


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