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[Xen-devel] Problems with enabling hypervisor C and P-state control

  • To: "Xen Developers" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Niraj Tolia" <ntolia@xxxxxxxxx>
  • Date: Wed, 22 Oct 2008 00:57:10 -0700
  • Delivery-date: Wed, 22 Oct 2008 00:57:57 -0700
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  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>


Is there any documentation on enabling hypervisor support for both C
and P-state control?

On xen-unstable and linux-2.6.18-xen.hg, if I enable cpuidle=1 on the
xen command line and then run xenpm, I will get output for C-states
(shown below) but it complains that "Xen cpufreq is not enabled!"

cpu id               : 0
total C-states       : 2
idle time(ms)        : 73264
C0                   : transition [00000000000000000000]
                       residency  [00000000000000000000 ms]
C1                   : transition [00000000000000025505]
                       residency  [00000000000000000000 ms]

(repeats for all cores)

However, CPU_FREQ depends on PROCESSOR_EXTERNAL_CONTROL being set to
'n'. There doesn't seem to be a way to enable/disable
CONFIG_PROCESSOR_EXTERNAL_CONTROL from menuconfig. I therefore
manually twiddled that bits in .config and enabled CPU_FREQ and
CPU_FREQ_TABLE (plus the performance governor). If I don't specify the
cpufreq option on the dom0 kernel command line, xenpm doesn't give me
C-state information anymore (output below) and will repeat the same
warning about cpufreq not being enabled.

cpu id               : 0
total C-states       : 0
idle time(ms)        : 0

(repeats for all cores)

If I then add cpufreq=xen to the kernel command line, xenpm's output
does not change. Any ideas on what I might be doing wrong? This is on
a quad-core Xeon (E7330).


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