On 9/16/2020 3:06 AM, Matthias Kaehlcke wrote:
On Tue, Sep 15, 2020 at 11:23:49PM +0200, Daniel Lezcano wrote:
On 15/09/2020 23:13, Matthias Kaehlcke wrote:
On Tue, Sep 15, 2020 at 10:55:52PM +0200, Daniel Lezcano wrote:
On 15/09/2020 19:58, Matthias Kaehlcke wrote:
On Tue, Sep 15, 2020 at 07:50:10PM +0200, Daniel Lezcano wrote:
On 15/09/2020 19:24, Matthias Kaehlcke wrote:
+Thermal folks
Hi Rajendra,
On Tue, Sep 15, 2020 at 11:14:00AM +0530, Rajendra Nayak 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?
Relative values may work for scheduling decisions, but not for thermal
management with the power allocator, at least not when CPU cooling devices
are combined with others that specify their power consumption in absolute
values. Such a configuration should be supported IMO.
The energy model is used in the cpufreq cooling device and if the
sustainable power is consistent with the relative values then there is
no reason it shouldn't work.
Agreed on thermal zones that exclusively use CPUs as cooling devices, but
what when you have mixed zones, with CPUs with their pseudo-unit and e.g. a
GPU that specifies its power in mW?
Well, if a SoC vendor decides to mix the units, then there is nothing we
can do.
When specifying the power numbers available for the SoC, they could be
all scaled against the highest power number.
The GPU was just one example, a device could have heat dissipating components
that are not from the SoC vendor (e.g. WiFi, modem, backlight), and depending
on the design it might not make sense to have separate thermal zones.
Is it possible to elaborate, I'm not sure to get the point ?
A device could have a thermal zone with the following cooling
devices:
- CPUs with power consumption specified as pmW (pseudo mW
- A modem from a third party vendor. The modem can dissipate
significant heat and allows to throttle the bandwidth for
cooling. The power consumption of the modem is given in
mW.
These could be crammed together in a small form factor
(e.g. ChromeCast or Chromebit) which makes it difficult to
discern with a sensor what exactly is generating the heat,
which is why you have a single thermal zone.
IPA is used as governor for this zone, it can't make accurate
decisions because one cooling device specifies it's power
consumption in pmW and the other in mW.
Is there a real example upstream for this, or is it a theoretical
problem (which can exist in the future) we are trying to solve?
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