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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.

> kvm -version : emulator version 0.12.5 (qemu-kvm-0.12.5), Copyright (c) 2003-2008 Fabrice Bellard

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

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2 Answers 2

up vote 3 down vote accepted
  1. the current qemu-kvm verison stands at 0.14
  2. Without guest configuration details there is no way to know what's going on, and provide advice.
  3. to troubleshoot kvm performance there is a tool called kvm_stat - it can show where the bottleneck is, if any
  4. 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
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Upgrading to 0.14 solved the problem, thanks! –  Park Young-Bae Jun 20 '11 at 18:19
    
glad to hear it helped –  dyasny Jun 20 '11 at 19:06

i experience with this problem last time (centos 5.4 64bit), i plan using kvm to replace xen, but we revert back to xen. i suspect the storage, but even using the local hdd, and KVM Paravirtualized drivers, kvm still got problem with high cpu load (may because of the kvm as kernel module, i don't know). i use for windows and linux.

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KVM is under very heavy development, and has been updated many times since 5.4. try it on 5.7 or 6.1 - you'll see the difference –  dyasny Jun 18 '11 at 10:13

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