[fedora-virt] Idle VM is hogging host cpu

[Dennis Jacobfeuerborn]

On 11/08/2010 02:22 PM, Sven Lankes wrote:
> On Mon, Nov 08, 2010 at 12:38:22PM +0000, Daniel P. Berrange wrote:
>
>> Try adding   divider=10  to the kernel boot command line for the guest.
>> This will make it use a 100HZ tick rate, instead of 1000HZ, lowering the
>> background idle load on the host. I doubt it accounts for 20%, but it is
>> always worth doing for RHEL5 kernels since they don't have tickless mode.
>
> I was seeing 10 - 15% cpu for the kvm process too. After adding
> divider=10 this dropped to 1%.
>

The fact that the guest needs special kernel parameters to run properly 
doesn't look right to me. Is there no way for KVM to handle this correctly?
Also I just imported this VM from my old Fedora 11 system on the new Fedora 
14 install and there I didn't see this behavior.

BTW this might or might not be related to a general problem with the kernel 
in Fedora 14:
https://bugzilla.redhat.com/show_bug.cgi?id=650934
https://bugzilla.redhat.com/show_bug.cgi?id=635813

Anyway, I'm off trying to boot my system with nohz=off and then add the 
divider thing to the guest to see if that has any impact.

Regards,
   Dennis