Xen cpufreq support status: how to notify hypervisor of frequency change?

["Matt T. Yourst" <yourst@yourst.com>]

Hi,

I previously posted a patch to make the dom0 cpufreq drivers properly use 
DOM0_MSR (instead of wrmsr) to adjust the processor frequency and voltage. 

This does indeed adjust the frequency, but Xen seems to have major latency 
problems whenever the frequency change takes affect, causing various problems 
like losing mouse events, uncontrolled keyboard repeats, and choppy audio and 
video playback for a few seconds after the shift.

This appears to happen because virtual timer interrupts do not get delivered 
on a regular basis for a few seconds following the frequency change.

Assuming we want to keep the cpufreq driver itself in dom0, what's the proper 
way to notify the hypervisor that the CPU frequency has just changed, so it 
can adjust its timers like the cpufreq driver on the native kernel does?

I'd really like to have cpufreq working properly under Xen (for both 
workstations and to a lesser extent servers), so what would be the best way 
to get this running?

- Matt Yourst

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 Matt T. Yourst               yourst@cs.binghamton.edu
 Binghamton University, Department of Computer Science
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