[CentOS-virt] 4 CPU with WinXP on Centos 5.5 KVM?

Fri May 28 22:49:36 UTC 2010
Kenni Lund <kenni at kelu.dk>

2010/5/28, Marcelino Mata <mmata at multimatic.com>:
>> >
>> > AFAIK KVM will always emulate CPUs not cores.
>> >
>> In fact, newer qemu/kvm supports "cores" parameter when used
>> with smp:
>> https://patchwork.kernel.org/patch/33961/
>> RHEL6 beta has new kvm and qemu - it is possible to use
>> multi-core CPU within virtualized winXP there.
>> Regards,
>>     Nenad
> I did mean cores not CPU's.  I am using Xeon W3520 (4 Core 2.67Ghz).

To avoid confusion, what you have on your hostside of CPUs and cores
are really not relevant here.

> Under Virtualbox, WinXP guest has no problem using all four cores with
> same Xeon W3520 computer.

In that case you now know that Virtualbox present your cores as cores
to XP, and not as CPUs.

> So far this appears to be limitation of KVM/Virtio drives with XP
> guests.  It does not appear to be KVM limitation since liveCD boot
> instead of XP.img boot shows 4 cores.

Again, if you do nothing, KVM will present your cores/CPUs as CPUs to
your XP guest. As XP only supports two CPUs, you'll only see two CPUs
in the guest. When you boot some Linux live image, you'll not hit that
limitation, as Linux supports way more than 2 CPUs.

It has nothing to do with VirtIO.

> I'm really only wanted confirmation that limitation can NOT be worked
> around.

Nenad wrote that RHEL 6 beta had a newer version of KVM, which
supports to present host CPUs/cores as cores to the guest. Eg. this
will solve your problem, but it sounds like you'll have to wait for
CentOS 6 or you can of course just install qemu-kvm yourself onto your
CentOS 5.5 installation.

> Running this under Windows 2003 server is also an option if it
> eliminates the 4 core problem.

Yes, running a Windows server edition supports more than two CPUs, so
this could also be a solution.

Best regards