Debian – KVM high CPU load

debiankvm-virtualizationwindows-server-2008

I have a dedicated machine running under Debian Squeeze. It's a reasonably good machine with 8 cores.

I started hosting a Windows Server 2008 guest with KVM, but the CPU load is extremely high (around 100%-200%) even when the guest is idle. What could explain such a behavior? Has anyone encountered it before? Does it come from KVM or Windows?

The Windows guest is up-to-date.

I don't know what more details to provide, but please ask for more information if you need!

Best Answer

the current qemu-kvm verison stands at 0.14
Without guest configuration details there is no way to know what's going on, and provide advice.
to troubleshoot kvm performance there is a tool called kvm_stat - it can show where the bottleneck is, if any
you might be seeing the qemu process going to 200% in top on the host, but do you really feel a performance hit on the host? Normally, when you assign more than one CPU to a VM, you might see the QEMU process showing high percentages, but that's only because top shows stats for a single CPU, and qemu-kvm is actually running several threads

Related Solutions

Debian – KVM – Problem installing Windows 2003 guest on Debian Lenny 64bit Host

So after reading more on http://www.linux-kvm.org/page/Code#Debian they say "It is important to use more recent kernel - 2.6.26 does not work well with kvm"

so I ran below since I have 64bit (linux-image-2.6-686 for 32bit)

apt-get -t lenny-backports install linux-image-2.6-amd64

then rebooted and tried to create my vm again and it WORKED!

debian:~# virt-install --connect qemu:///system -n win2k3 -r 2048 -c /home/win2k3.iso -f /home/win2k3.img -s 20 --nonetworks --noautoconsole --vnc --os-type=windows --os-variant=win2k3 --hvm --accelerate


Starting install...
Creating storage file win 100% |=========================|  20 GB    00:00     
Creating domain...                                                 0 B 00:00 
Domain installation still in progress. Waiting for installation to complete.

I hope this helps anyone who might stumble here.

Windows XP guest problems

first of all, make sure kvm modules are actually loaded using lsmod. The fact that it took you 6 hours to install, is already a serious indication of a flaw in your setup. It should take up to 20 minutes, depending on the storage speeds, on any modern host. second, if kvm is actually loaded, please post the qemu and kvm versions you're running as well as the VM command line you're using. With those, recommendations can be provided

As for real life success stories - I've been running and supporting hundreds (if not thousands) of windows deployments on kvm in various setups since 2008, and if performance issues were encountered, they always were due to hardware or misconfigurations.

Best Answer

Related Solutions

Debian – KVM – Problem installing Windows 2003 guest on Debian Lenny 64bit Host

Windows XP guest problems

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