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RE: [Xen-devel] Cpufreq on k8 with xen dom0

To: "Goswin von Brederlow" <brederlo@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Cpufreq on k8 with xen dom0
From: "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
Date: Thu, 27 Sep 2007 10:04:09 -0500
Cc: geaaru@xxxxxxxxx, Xen-Devel ML <xen-devel@xxxxxxxxxxxxxxxxxxx>, Bhavana Nagendra <bnagendr@xxxxxxxxxx>
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Thread-topic: [Xen-devel] Cpufreq on k8 with xen dom0
> >  >  is there a patch for xen-source-2.6.20-r3 for use cpufreq on 
> >> turion64?
> >> I'm using xen-sources of gentoo portage.
> >> Thanks in advance.
> >
> > It's still in development; there's a version available
> > that will let you userspace tools in dom0 to monitor 
> > and control frequency changes but true ondemand dynamic
> > scaling still needs some work.
> >
> > Email me privately if you're interested in helping and
> > willing to be a test subject.  Thanks.
> I'm verry interested. I have xen on my laptop and when on battery mode
> that totaly drains power. So when traveling I have to boot non XEN
> limiting me to dom0.
> It shouldn't be too hard to write a little application that will scale
> frequency depending on the sum of cpu usage of all domains. The info
> is shown in xentop so it should be simple of sampling that once every
> X second and sclaing for it.
> But even a simple "make it slow" option would be just fine.

The current version of xen-unstable.hg has Keir's rewrite of
most of Rik's and my code for support PowerNow!.  A dom0 with
cpufreq support enabled can use the performance, powersave,
and userspace governors to change frequency. 

You'll need to build the latest repository of xen-unstable.hg
and linux-2.6.18.hg with the cpufreq build config options
enabled, and pass "cpufreq" on the Xen command line.  
Power management should come up normally, and running
`echo "powersave" >
should force the system to minimum power.  The same command
with "performance" should set it to maximum power.  The
same command with "userspace" will create a 
/sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed file,
and writing a frequency value to that will cause the system
to move to the nearest supported frequency to that value.
A usermode daemon like cpuspeed
can be modified to use the Xen getcpuinfo sysctl to read
the Xen usage values and write to the scaling_setspeed file,
though I haven't had time to do that yet.

The ondemand governor won't be supported unless getcpuinfo
becomes a platform op hypercall.  Rik, what's the status
on that?

-Mark Langsdorf
Operating System Research Center

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