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Thread: Awkward Linux Power Management With Xen

  1. #1
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    Default Awkward Linux Power Management With Xen

    Phoronix: Awkward Linux Power Management With Xen

    If you happen to be running a Linux system with Xen support enabled, beware there may be odd behavior with the Linux kernel's power management -- it can easily move in either direction.

    http://www.phoronix.com/vr.php?view=16715

  2. #2
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    Odd. This is without even using xen? Because the latest debian kernels include xen by default.

  3. #3
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    Quote Originally Posted by Cyborg16 View Post
    Odd. This is without even using xen? Because the latest debian kernels include xen by default.
    I can't find out from the text what it means too.
    "when the Linux kernel is booted with the Xen Hypervisor support enabled, but not looking when running any DomU guests or other changes."
    I guess he simply means running as dom0. I noticed this on my laptop: when I run my Archlinux as dom0 it eats way more power than running it natively.

  4. #4
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    Looks like it's using fewer cores to do the same amount of work (would explain more power usage--due to being unable to enter a lower power state--and less performance in a threaded benchmark), but I'm no expert in xen or interpreting benchmarks, so....

  5. #5
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    not.sure I understand what this is supposed to mean either. Should we compile kernels w/o xen or just use some 'noxen' boot or .. ?

  6. #6
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    Default Xen ACPI cpufreq patches

    The power consumption differences are explained by the lack of Xen dom0 ACPI cpufreq patches in the current upstream Linux kernel v3.x. This was already pointed out earlier in the comments for the KVM vs Xen vs Virtualbox benchmark, where the lack of acpi cpufreq patches caused the weird performance difference (the Xen host CPU never entered the turbo mode/states causing lower performance compared to others in that benchmark). The link to the previous comment is here: http://phoronix.com/forums/showthrea...635#post238635

    Xen dom0 ACPI cpufreq patches are currently being prepared for submission to upstream Linux 3.3 kernel. The patches are currently available in "git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git devel/acpi-cpufreq.v4".

  7. #7
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    Default xen.org re-run of the Phoronix benchmark

    Here's a re-run of the Phoronix Xen vs. KVM vs. VirtualBox benchmarks, with the missing Xen dom0 ACPI cpufreq patches added to the dom0 kernel: http://blog.xen.org/index.php/2011/1...-vs-kvm-redux/

    The performance numbers are very different there. Please take a look.

    The same patches also make it possible to use the lower CPU power states, to use less power and enable power saving. So it would be interesting to re-run this power usage benchmark with the Xen dom0 acpi cpufreq patches added to the dom0 kernel.

  8. #8
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    The Xen ACPI cpufreq / power management patches are now included in upstream Linux 3.4.x and later kernel versions. The driver in question is called "xen_acpi_processor.ko".
    Last edited by pasik; 07-02-2012 at 06:49 PM.

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