status of cpufreq code support

status of cpufreq code support

[Jan Beulich]

Can someone give me an understanding what the current position on allowing dom0 to manipulate the CPU frequency is? The
config options haven't been disabled for a while, but when I recently did a build there were still symbols missing for
some of the drivers. Also, I continue to believe that playing with the CPU frequency behind the back of Xen isn't the
best idea.

Thanks, Jan

Re: status of cpufreq code support

[Keir Fraser]

On 2 Aug 2006, at 15:06, Jan Beulich wrote:

> Can someone give me an understanding what the current position on 
> allowing dom0 to manipulate the CPU frequency is? The
> config options haven't been disabled for a while, but when I recently 
> did a build there were still symbols missing for
> some of the drivers. Also, I continue to believe that playing with the 
> CPU frequency behind the back of Xen isn't the
> best idea.
>
> Thanks, Jan

I've been thinking about it and come to the conclusion that the right 
thing is to let dom0 fiddle with the CPU frequencies, subject to:
  1. It should have a 1:1 mapping to physical CPUs (i.e., VCPU0 always 
runs on CPU0, VCPU1 on CPU1, etc.). Preferably we'd also pass real 
topology info to dom0 too, so that it can do the right thing for 
multi-core and hyperthreads.
  2. We need an interface for dom0 to tell Xen that the speed is 
changing, so that scale factors can be updated.

  -- Keir