RE: [Xen-users] Power Management (cpufreq) in Xen 3.3

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Mike Brady
>Sent: Friday, October 24, 2008 1:26 AM
>
>I am having some difficulty with power management in Xen 3.3.
>
>I have an Intel S5000PSL motherboard with Xeon 5410 running Centos 5.2
>x86_64.  With the Centos Xen/kernel, /proc/cpuinfo shows the CPU speed
>changing with load over time.
>
>I have recently upgraded Xen to 3.3 using the RPMs available from
>http://www.gitco.de/repo/xen3.3.0 and changed my grub config to 
>
>title CentOS (2.6.18-92.1.13.el5xen)
>        root (hd0,0)
>        kernel /xen.gz-3.3.0 cpufreq=xen
>        module /vmlinuz-2.6.18-92.1.13.el5xen ro
>root=/dev/vg_system/lv_root
>        module /initrd-2.6.18-92.1.13.el5xen.img
>
>xm dmesg shows that the cpufreq=xen has been picked up, but gives no
>indication that it is doing anything.  /proc/cpuinfo no longer shows a
>variable CPU frequency.
>
>How do I tell if the power management features are working?  I had
>expected to see something more in the xm dmesg output and/or 
>to continue
>to see changes in /proc/cpuinfo.
>
>Can someone enlighten me as to what it is that I am missing please.
>

Nothing is missing except a tool. :-) /proc/cpuinfo or other linux 
equivalent interfaces can't reveal cpufreq information, because
now freq scaling is controlled by Xen instead of dom0, and there's
no fixed mapping between dom0's vcpu and underlying real cpus.
In 3.3, xen does exports hypercall to query runtime cpufreq info
in libxc library, however no tool is using at the time. In post-3.3,
we actually developed a so-called 'xenpm' utility for such purpose.
We're back-porting it to xen-3.3 tree, and you should be able to
see it soon.

For now, if you don't see any error-type msg, it just indicates 
xen-cpufreq working well, but yes, no detail info yet.

Thanks,
Kevin
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