Re: Power Management framework proposal

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sun, 2007-07-22 at 10:26 -0700, Arjan van de Ven wrote:
> On Sat, 2007-07-21 at 23:49 -0700, david@lang.hm wrote:
> 
> > this approach would allow the transition of ALL drivers to the new mode of 
> > operation in one fell swoop, and then adding additional power management 
> > features is just adding to the existing list rather then implementing new 
> > functions.
> 
> 
> I have a concern with this approach though. It seems to assume that
> there is one global thing somewhere that sets the system state; in my
> experience that is the wrong approach; in fact there is a very definite
> evidence that there are many decisions on power that are to be made
> local at a high frequency. An example of this is the processor speed;
> the ondemand governer does exactly this for the cpus that can switch
> speeds fast; it's just impossible to beat such a local, fast decision
> with anything on a global scale.
> 
> On the other hand, some things (the high level goals and constraints)
> are obviously global.

I think we need a set of constraints that trickle down the power tree
and limit what a given driver can do locally.

Ben.