Hi, On Mon, Sep 14, 2020 at 10:44 PM Rajendra Nayak <rnayak@xxxxxxxxxxxxxx> wrote: > > Hi Rob, > > There has been some discussions on another thread [1] around the DPC (dynamic-power-coefficient) values > for CPU's being relative vs absolute (based on real power) and should they be used to derive 'real' power > at various OPPs in order to calculate things like 'sustainable-power' for thermal zones. > I believe relative values work perfectly fine for scheduling decisions, but with others using this for > calculating power values in mW, is there a need to document the property as something that *has* to be > based on real power measurements? > > Looking at the bindings, > > dynamic-power-coefficient: > $ref: '/schemas/types.yaml#/definitions/uint32' > description: > A u32 value that represents the running time dynamic > power coefficient in units of uW/MHz/V^2. The > coefficient can either be calculated from power > measurements or derived by analysis. > > The dynamic power consumption of the CPU is > proportional to the square of the Voltage (V) and > the clock frequency (f). The coefficient is used to > calculate the dynamic power as below - > > Pdyn = dynamic-power-coefficient * V^2 * f > > where voltage is in V, frequency is in MHz. > > .. the 'can either be calculated from power measurements or derived by analysis' > tells me we don't mandate that this be based on real power measurements. > If we do, then perhaps that needs to be mentioned explicitly? To me, the phrase "derived by analysis" doesn't mean that the number is allowed to be in completely made up units. It means it's still supposed to be in the same units but it's OK if you didn't integrate a Coulomb counter into your system. It's kinda like saying that the police can give you a speeding ticket by either measuring your speed with a radar gun or by checking a clock when your car passed two known places and calculating your speed based on that. The radar gun is a direct measurement whereas the other is derived by analysis. In both cases you're still talking about a speed in terms of Miles per Hour (or kilometers per hour in more sane countries). -Doug
