[Gllug] Hardware problems / good replacements

Richard W.M. Jones rich at annexia.org
Sat Feb 11 12:00:22 UTC 2012

On Fri, Feb 10, 2012 at 11:05:15PM +0000, Phil Reynolds wrote:
> On 10/02/12 22:05, Richard W.M. Jones wrote:
> > On Fri, Feb 10, 2012 at 07:40:21PM +0000, Phil Reynolds wrote:
> >> Since I upgraded my motherboard, processor and memory last summer I have
> >> found that virtual machines (be they under kvm or virtualbox) perform
> >> less well than expected.
> > 
> > What test are you running to determine this?
> Nothing very scientific - just that they are (or were, before the BIOS
> upgrade, at least) noticeably much slower than on the previous 3 core
> processor.

I'm surprised that a BIOS update made any difference.  I wasn't aware
that virtualization extensions could be disabled on AMD; on Intel it
is (or used to be) a problem that virtualization would be disabled by
the BIOS and couldn't be reenabled, requiring a BIOS update or even a
replacement motherboard to rectify.  Perhaps the BIOS update just
fixed some clock speed or memory settings, making the machine
generally faster.

It's academic now, but before the BIOS update did you check the
obvious stuff; all cores enabled? core speed? BogoMIPS? memory
settings set for maximum performance ...?

> > The second problem is Debian squeeze ... because it's old.  Using the
> > latest kernel, qemu-kvm and libvirt should yield significantly better
> > results.
> I tried a later qemu-kvm... it didn't seem to make much difference on
> what I could actually get it to do at the time. I will try it again
> fairly soon, if this problem persists.

You need to upgrade the whole stack, from kernel up through userspace
tools.  This needs coordination from all components.

> > A 6 core Phenom surely has enough oomph to run virtual machines fast
> > (although not as fast as if you're using virtio and the latest
> > software).  To check, you could compare your cpu flags to this page:
> > 
> > http://virt-tools.org/learning/check-hardware-virt/
> A pass, as ever when I checked.

Also check that KVM is actually being used.  You should see the
'kvm_amd' module is loaded, and there should be no warnings or errors
in 'dmesg' about virtualization being disabled.


Richard Jones
Red Hat
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