Re: Alternative Concept [Was: Re: [RFC] CPUFreq PowerOPintegration, Intro 0/3]

[Dominik Brodowski <linux@dominikbrodowski.net>]

Hi,

On Sun, Oct 08, 2006 at 09:28:15AM -0500, Woodruff, Richard wrote:
> > D) Verification
> > 
> > So, how to do this verification? Basically, there are two approaches:
> > 
> > 1) ask every other subsystem whether the new value is OK with it.
> > 	This is what cpufreq currently suggests to do. It is evident
> > 	that this gets overly complicated with lots of dependencies
> > 	and dependencies within the dependencies -- both in terms
> > 	of concept and in terms of time the verification code takes
> > 	to execute.
> > 	Advantages:
> > 	- easy to expand, also in runtime (e.g. USB system is
> > 		modprobed and telling you of a new minimum voltage
> > 		requirement on certain circumstances)
> > 	- does not limit choices for each knob
> > 	Disadvantages:
> > 	- might get very complex
> > 
> > 2) look up all valid states in a table
> > 	This is basically what PowerOP and the "operating points"
> > 	concept suggests: if you want to change one value, you check
> > 	what operating points a) contain the new value and b) is
> > 	most suitable to you.
> > 	Advantages:
> > 	- fast
> > 	- pre-defined set of operating points which the system
> > 	  designer is comfortable with
> > 	Disadvantages:
> > 	- needs to be limited to "core" of the system as else
> > 	  the tables may get overly large
> > 	- limits the choices
> 
> That is a pretty good summary.
> 
> Depending on your operating point definition you don't always have to
> limit yourself here.  An operating point parameter need not directly be
> associated with the physical value of the domain it represents.  Meaning
> you don't need to put 1.05 volts in for the parameter, you can define it
> as some other value which needs translating/defining by the core.

First, thanks for your insightful comments. Second, well, we can of course
use some discrete values instead of "real" values -- however, if we get the
chance, I think it's nicer to put the "real" values there. Unless we need
floating point ;)

Thanks,
	Dominik