[CentOS-virt] High CPU usage when running a CentOS guest inVirtualBox

Tue Sep 1 16:14:56 UTC 2009
Akemi Yagi <amyagi at gmail.com>

On Tue, Sep 1, 2009 at 5:33 AM, Hildebrand, Nils,
232<Nils.Hildebrand at bamf.bund.de> wrote:
> Hi,
> I just closed a service-request with sun.
> Topic: Why is Win32 slower running with two CPUs under VBox 3 than
> running with one CPU on VBox 2?
> I am running VBox on CentOS 5 64 bit (AMD Athlon Dual Core).
> The problem is - according to sun - the IO-APIC-emulation:
> On 32-bit-systems this io-apic-emulation (needed for passing interrupts
> between CPUs) has to use a full software-context-switching - making
> things slow.
> I tried recreating the problem with CentOS 5 64 Bit as VM, two CPUs: no
> problem
> With CentOS 5 32 Bit as VM: same problem.
> I guess some problems with multi-cpu-VMs using 32-bit-operating-systems
> on a 64-bit hardware are related to this - no matter if you are using
> xen (fully virtualized), VirtualBox or VMWare.

Interesting.  I do not have any 32-bit multi-cpu VMs myself, but I do
have access to such guests running on a host (64-bit) using kvm.  Both
CentOS-5 32-bit VM and CentOS-4 32-bit VM show normal load (near 100%
idle on all cpus).  They have the divider=10 option by the way.