Re: CVS commit: src/sys

[Jukka Ruohonen <jruohonen%iki.fi@localhost>]

On Sun, Aug 08, 2010 at 04:58:42PM +0000, Jukka Ruohonen wrote:
> Merge P-state support for acpicpu(4).

Hi.

I'll post this note about conclusions from various informal discussions
regarding acpicpu(4) and CPU power management generally.

In my opinion, it is increasingly evident that we will need a well-defined,
machine-independent interface and KPI especially for CPU frequency
management. I am very much willing to work with such a KPI, but the goal
here has been to first get the ACPI implementation ready, as a stand-alone
and modular component with minimal changes to existing MD code.

There is still much work to do with the ACPI CPU driver. But once it is
ready and robust, we can continue to evaluate how much of this is
x86-specific, what would be the API requirements, what potential efficiency
concerns need to be taken into account, how CPU power management might be
driven by the scheduler, and so forth.

So the MD things done here are more or less kludges to patch up things that 
were already more or less kludges. The existing PowerNow! and EST need to
be eventually rewritten from scratch.  The backwards compatibility need to
broken at some point.  The sysctl(8) solution and user space "governors"
need to be deprecated to reach the full potential of modern CPU power
management on x86 and presumably on other architectures as well.

- Jukka.