Messages in this thread |  | | From | Vincent Guittot <> | Date | Tue, 21 Nov 2017 17:08:34 +0100 | Subject | Re: [PATCH 4/4] cpu_cooling: Drop static-power related stuff |
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Hi Lukasz
On 21 November 2017 at 16:56, Lukasz Luba <llu.ker.dev@gmail.com> wrote: > On 21/11/17 14:06, Daniel Lezcano wrote: >> >> On 21/11/2017 12:30, Ionela Voinescu wrote: >> >> [ ... ] >> >>> A DT model would be easy to support with the current code but it would >>> be very inaccurate. >> >> >> Why ? >> >> [ ... ] >> > Hi all, > > The DT solution won't fly, the reason can be found below. > > I agree with Ionela and Punit that the Juno board is not > the best platform to test the static power impact on IPA. > In some other platforms the static power can be 50% or more > of the total power, so it cannot be neglected. > > These are the issues. > The static power equation is complicated, here is one known to me. > The leakage function is exponentially influenced by current circuit > supply voltage, body-bias and some constants K_{4,5}. > > P_{leak} = L_{g}*V_{dd}*K_{3}*e^{K_{4}*V_{dd}}*e^{K_{5}*V_{bs}}+| > V_{bs}|*I_{Ju}
You forgot one main contributor of static leakage: the temperature
> > It can also vary depending on technology (CMOS, FinFET, etc). > > It would be really hard to approximate by i.e. a polynomial > function with inputs from DT. One size does not fit all.
But can't we linearized around the target temp ? that were we want to be accurate
Regards, > > The equation can also tell you some interesting things about > the manufacturing process. Exposing such information might be the last > thing the vendors want to. > That's why the vendors might want to implement whole > thermal management in the firmware or skip static power and > rely on IPA adaptation. > They can also use a different api in IPA, when they have some mechanism > to measure power in firmware, it can be feed into IPA. > > Anyway, I would recommend to keep it as is, to have a complete > power model in the kernel. > The code without static power routines looks awkward to me. > From my side - NACK for the patch which removes static power. > > Regards, > Lukasz Luba
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