KVM uses only one CPU

[larsg]

Hi,

I recently installed KVM on my workstation (Ubuntu 9.04 64 Bit with Intel Core2 Quad).
I set up an virtual machine with 4 CPUs (same as the host) with CentOS 5.2 as guest operating system.

When I start several programs to get the cpu usage up, top (in the vm) tells me that all 4 cpus are 90% to 100% in use, but on the host only one cpu is in use the other 3 have about 90% idle.
Furthermore the vm-process has never over 100% cpu usage.

I migrated the vm with qemu-img and easily get 180% cpu usage using vmware.

I made sure that the virtualisation technologie is activated in the BIOS (vmware complained) but that didn't change anything.
I did an internet search but couldn't find anybody with a similar problem let alone a solution.

Does anybody of you know this problem? Help would be very much appreciated.

[Rubberman]

Have you enabled the VTx extensions in the system bios? They are likely required in order to make use of the additional cores.

[larsg]

Thanks for your response.

After vmware complained I activated the following:

Intel Virtualization Technology <enabled>
VT for Directed I/O (VT-d) <enabled>

I also activated "Virtual Appliance (VA)" (just in case):

VA Operation <enabled>
User confirmation requiered <no>
VA Configuration Interace <unlocked>

As far as I understand it "Intel Virtualization Technology" is VT-X, but it didn't change anything...

[Rubberman]

Does the guest OS think it has 4 cores? If so, then possibly KVM only simulates the cores, but still only uses one on the host. I don't really know since I haven't used KVM. I use VirtualBox which only just released version 3 which finally supports (with problems) multiple cores.

[larsg]

Yes, the OS finds all 4 cores.

Anyway, I think I found the problem.
I experimented with other distributions and the kvm-settings today and it seems the problem occurs when I install a 32Bit-OS in a 64Bit-VM. After I changed the cpu-settings of kvm all 4 cores are used on the host (over 200% cpu usage).