FAQ
I've got a three Centos 5.5 KVM severs, but only one of them is presenting
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 and
the kvm-clock source appeared.

Any ideas why I'm not seeing kvm-clock with my Athlon X2 processors, or is
there another difference I haven't caught?


Steve

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  • Steven Ellis at Nov 4, 2010 at 12:25 am

    On Thu, 04 Nov 2010 17:03:33 +1300, Steven Ellis wrote:

    I've got a three Centos 5.5 KVM severs, but only one of them is
    presenting
    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 and
    the kvm-clock source appeared.

    Any ideas why I'm not seeing kvm-clock with my Athlon X2 processors, or is
    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 at vger.kernel.org/msg10193.html

    This finally led to the following docs
    *
    http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.5/html/Virtualization_Guide/chap-Virtualization-KVM_guest_timing_management.html

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

    Steve

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