[CentOS-virt] KVM + virsh nodeinfo + CentOS 6.3

Wed Oct 24 15:58:00 UTC 2012
bertrand.louargant at atoutlinux.net <bertrand.louargant at atoutlinux.net>

Hello,

You have a NUMA (Non Uniform Memory Access) machine, which mean that each
processor has its own memory controller.
virsh nodeinfo give you 2 NUMA cells with 1 CPU socket each: 2 NUMA cells x 1CPU
socket x 6 Core(s) per socket x 2 threads per core = 24 "cores".

The NUMA concept is really important, especially  in virtualization.
If you have a virtual machine with vCPUs spread across more than one NUMA cell,
performances will drop drastically.

Maybe you cannot assign more than 4 cPUs to your VM because Libvirt cannot pin
them all on the same NUMA cell ...
You can try to specify the NUMA architecture in the xml config.

Br,
Bertrand.

Le 24 octobre 2012 à 17:14, Zoltan Frombach <zoltan at frombach.com> a écrit :
> Hi,
>
> Please let me know in case I am posting my question to the wrong forum.
> I apologize if that is the case!
>
> Here is my question:
>
> We run CentOS 6.3 on a server with dual Xeon CPU's. Our "dual blade"
> server uses this motherboard:
> http://www.supermicro.com/products/motherboard/Xeon/C600/X9DRT-HF.cfm
>
> We have two of these CPUs installed and working:
> Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz
> (
> http://ark.intel.com/products/64594/Intel-Xeon-Processor-E5-2620-15M-Cache-2_00-GHz-7_20-GTs-Intel-QPI
> )
>
> cat /proc/cpuinfo correctly reports a total of 24 cores (2 x 6 phisycal
> cores plus 2 x 6 hyperthreading cores)
>
> However, I get this output from virsh nodeinfo :
>
> # virsh nodeinfo
> CPU model: x86_64
> CPU(s): 24
> CPU frequency: 2000 MHz
> CPU socket(s): 1
> Core(s) per socket: 6
> Thread(s) per core: 2
> NUMA cell(s): 2
> Memory size: 16303552 kB
>
> As you can see, virsh nodeinfo reports only 1 CPU socket while in fact
> we have two CPU's.
>
> I would like to know if this is normal? Why does virsh reports only one
> physical CPU ??
>
> Also, when we try to run a guest OS (Debian Linux "squeeze") with more
> than 4 vcpu's assigned to the VM, the guest OS won't boot up. The
> guest's kernel stuck on a screen right after it detected the /dev/vda
> block device and its partitions. We're using the VirtIO driver, of
> course. If I assign only 4 (or less) vcpu's to the guest OS it works
> fine. I have tried to upgrade the Linux kernel on the guest from debian
> backports, it did not help, we're experiencing the same issue with both
> the 2.6.32 and 3.2 Linux kernels. What could be causing this?
>
> On the host, we use the Linux kernel that came with CentOS 6.3 :
> 2.6.32-279.11.1.el6.x86_64 #1 SMP Tue Oct 16 15:57:10 UTC 2012 x86_64
> x86_64 x86_64 GNU/Linux
>
> Thanks,
>
> Zoltan
> _______________________________________________
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> CentOS-virt at centos.org
> http://lists.centos.org/mailman/listinfo/centos-virt
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