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Hi, I recently installed KVM on my workstation (Ubuntu 9.04 64 Bit with Intel Core2 Quad). I set up an virtual machine with 4 CPUs (same as the host) with ...
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  1. #1
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    KVM uses only one CPU


    Hi,

    I recently installed KVM on my workstation (Ubuntu 9.04 64 Bit with Intel Core2 Quad).
    I set up an virtual machine with 4 CPUs (same as the host) with CentOS 5.2 as guest operating system.

    When I start several programs to get the cpu usage up, top (in the vm) tells me that all 4 cpus are 90% to 100% in use, but on the host only one cpu is in use the other 3 have about 90% idle.
    Furthermore the vm-process has never over 100% cpu usage.

    I migrated the vm with qemu-img and easily get 180% cpu usage using vmware.

    I made sure that the virtualisation technologie is activated in the BIOS (vmware complained) but that didn't change anything.
    I did an internet search but couldn't find anybody with a similar problem let alone a solution.

    Does anybody of you know this problem? Help would be very much appreciated.

  2. #2
    Linux Guru Rubberman's Avatar
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    Have you enabled the VTx extensions in the system bios? They are likely required in order to make use of the additional cores.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

  3. #3
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    Thanks for your response.

    After vmware complained I activated the following:
    Intel Virtualization Technology <enabled>
    VT for Directed I/O (VT-d) <enabled>

    I also activated "Virtual Appliance (VA)" (just in case):
    VA Operation <enabled>
    User confirmation requiered <no>
    VA Configuration Interace <unlocked>

    As far as I understand it "Intel Virtualization Technology" is VT-X, but it didn't change anything...

  4. #4
    Linux Guru Rubberman's Avatar
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    Does the guest OS think it has 4 cores? If so, then possibly KVM only simulates the cores, but still only uses one on the host. I don't really know since I haven't used KVM. I use VirtualBox which only just released version 3 which finally supports (with problems) multiple cores.
    Sometimes, real fast is almost as good as real time.
    Just remember, Semper Gumbi - always be flexible!

  5. #5
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    Yes, the OS finds all 4 cores.

    Anyway, I think I found the problem.
    I experimented with other distributions and the kvm-settings today and it seems the problem occurs when I install a 32Bit-OS in a 64Bit-VM. After I changed the cpu-settings of kvm all 4 cores are used on the host (over 200% cpu usage).

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