Re: [PATCH/RFC 0/2] arm64: dts: renesas: Re-add voltages to OPP tables

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Lukasz,

On Tue, Dec 10, 2024 at 3:28 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Wed, Nov 13, 2024 at 5:58 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > On Mon, Nov 4, 2024 at 4:15 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > > On Mon, Oct 28, 2024 at 2:41 PM Lukasz Luba <lukasz.luba@arm.com> wrote:
> > > > On 10/28/24 11:34, Geert Uytterhoeven wrote:
> > > > > On Fri, Oct 25, 2024 at 5:40 PM Lukasz Luba <lukasz.luba@arm.com> wrote:
> > > > >> On 10/22/24 14:36, Geert Uytterhoeven wrote:
> > > > >>> On Tue, Oct 8, 2024 at 11:14 AM Geert Uytterhoeven
> > > > >>> <geert+renesas@glider.be> wrote:
> > > > >>>> When CONFIG_ENERGY_MODEL=y, an error is printed on RZ/G2E and R-Car E3:
> > > > >>>>
> > > > >>>>       cpu cpu0: EM: invalid perf. state: -22
> > > > >>>>
> > > > >>>> This happens because the Operating Points Parameters tables do not list
> > > > >>>> voltages, as they are all identical.  Previously, it was assumed they
> > > > >>>> were optional, and unused, when none of the CPU nodes is tied to a
> > > > >>>> regulator using the "cpu-supply" property.  This assumption turned out
> > > > >>>> to be incorrect, causing the reported error message.
> > > > >>>>
> > > > >>>> This RFC patch series fixes this by adding the missing voltages.
> > > > >>>>
> > > > >>>> Note that the Energy Model calculates energy efficiency by dividing the
> > > > >>>> (estimated) CPU power consumption by CPU core clock frequency.  When all
> > > > >>>> voltages have the same value, the former is proportional to clock
> > > > >>>> frequency, and energy efficiency becomes a constant.  Hence all
> > > > >>>> operating points are considered to have the same efficiency, and the
> > > > >>>> Energy Model always picks the one with the highest clock rate (see also
> > > > >>>> [1]).
> > > > >>>>
> > > > >>>> Alternatively, the Energy Model could be changed to silently ignore OPP
> > > > >>>> tables with missing frequencies.  IMHO this is not an unusual case.
> > > > >>>>
> > > > >>>> Which approach should be taken?
> > > > >>>> Thanks for your comments!
> > > > >>>
> > > > >>> Any comments from the Energy Model and PM people?
> > > > >>
> > > > >> My apologies for delay.
> > > > >>
> > > > >> So you had issue with bogus Voltage values and removed them.
> > > > >>
> > > > >> There is another way to setup EM properly, via DT:
> > > > >> "opp-microwatt" [1].
> > > > >>
> > > > >> That micro watt value won't confuse other subsystems, like
> > > > >> your regulator fwk. It will only be used by the EM fwk.
> > > > >>
> > > > >> This would be an alternative to your voltage values.
> > > > >> Sounds better to you?
> > > > >
> > > > > For opp-microwatt, I do need to know the actual power consumption
> > > > > of the core, right?
> > > >
> > > > Correct. You can try to derived that in a way you did and put below.
> > > > Although, Dhrystone is a synthetic micro-benchmark with small
> > > > impact to data caches, so it will not use much power.
> > >
> > > Do you have a suggestion for a better load test? stress-ng?
> > >
> > > > > Full system power consumption while running the in-kernel
> > > > > Dhrystones benchmark:
> > > > >
> > > > > 800 MHz: avg 4972,55 mW, stdef 20,474 mW
> > > > > 1000 MHz: avg 5025,93 mW, stdef 18,644 mW
> > > > > 1200 MHz: avg 5059,63 mW, stdef 15,425 mW
> > > >
> > > > Right. From those power values can be try to derive the
> > > > 'CPU only power' values - assuming only one core was
> > > > running the test.
> > > >
> > > > AFAIU you don't have proper DVFS due to missing voltage scaling.
> > >
> > > Indeed.
> > >
> > > > Therefore...
> > > > Out of that I got these CPU power values:
> > > > 800MHz -> 174mW
> > >
> > > => 217.5 µW/MHz
> > >
> > > > 1000MHz -> 212mW
> > >
> > > => 212 µW/MHz
> > >
> > > > 1200MHz -> 261mW
> >
> > BTW, how did you get from my avg mW values above to your CPU power mW
> > values? I seem to be missing something...
>
> Ping...

Gentle ping.
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds