[libvirt] HELP: after host upgrade to F11, guest runs extremely slow

Chris Lalancette clalance at redhat.com
Tue May 26 06:49:32 UTC 2009

Gerry Reno wrote:
> Gerry Reno wrote:
>> Gerry Reno wrote:
>>> Daniel P. Berrange wrote:
>>>> On Sat, May 23, 2009 at 03:43:12PM -0400, Gerry Reno wrote:
>>>>> I upgraded the host from F10 to F11 (x86_64) with no issues.  Now when I 
>>>>> start a F10 (i386) guest it runs very very slow.  I also see messages on 
>>>>> the guest boot console about "clocksource tsc unstable" and some kernel 
>>>>> oops.  Once it got far enough to start network I logged in and checked 
>>>>> the clocksource and it currently is 'acpi_pm' even though the kernel 
>>>>> line says clocksource=pit.  The available clocksources are acpi_pm, 
>>>>> jiffies, and tsc.  I do not see 'pit' in the list.  How do I fix this issue?
>>>> If the guest runs 'extrememly' slowly then the most like thing is that 
>>>> it has fallen back to using QEMU emulation, instead of KVM hardware
>>>> acceleration. Check the /var/log/libvirt/qemu/$GUEST.log to see if there
>>>> is any mesage about not being able to open /dev/kvm.  Also make sure that
>>>> KVM modules are loaded, and that 'virsh capabilities' lists KVM as a valid
>>>> domain.
>>>> Daniel
>>> Ok, I checked the guest log and it says:
>>> /dev/kvm: no such file or directory.
>>> So how do I make this node?  Shouldn't libvirt have made it for us?
>> Ok, once I got both kernel modules loaded, it created the /dev/kvm
>> device and now everything runs fine.
> Well, not quite so fine.  If I reboot the machine then the kvm modules
> are no longer loaded.  How do I keep these modules loaded?

I'm assuming that you haven't installed qemu from the F-11 packages.  If you
install the qemu-system-x86 on F-11, it comes with a file
/etc/sysconfig/modules/kvm.modules.  On bootup, any scripts in that directory
are executed, and that command automatically loads the appropriate modules for
you.  If you don't want to install the F-11 qemu-system-x86 package for some
reason, you'll have to arrange to do the same with a custom script in that
directory, or just in /etc/rc.d/rc.local.

Chris Lalancette

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