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Documentation: EM: Add artificial EM registration description

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Add description about new artificial EM registration and use cases.
Update also the documentation with the new .get_cost() callback
description and usage.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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Lukasz Luba 2022-03-21 09:57:27 +00:00 committed by Rafael J. Wysocki
parent 16857482b8
commit 015f569c46
1 changed files with 20 additions and 0 deletions
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Documentation/power/energy-model.rst
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@ -123,6 +123,26 @@ allows a platform to register EM power values which are reflecting total power
(static + dynamic). These power values might be coming directly from
experiments and measurements.
Registration of 'artificial' EM
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
There is an option to provide a custom callback for drivers missing detailed
knowledge about power value for each performance state. The callback
.get_cost() is optional and provides the 'cost' values used by the EAS.
This is useful for platforms that only provide information on relative
efficiency between CPU types, where one could use the information to
create an abstract power model. But even an abstract power model can
sometimes be hard to fit in, given the input power value size restrictions.
The .get_cost() allows to provide the 'cost' values which reflect the
efficiency of the CPUs. This would allow to provide EAS information which
has different relation than what would be forced by the EM internal
formulas calculating 'cost' values. To register an EM for such platform, the
driver must set the flag 'milliwatts' to 0, provide .get_power() callback
and provide .get_cost() callback. The EM framework would handle such platform
properly during registration. A flag EM_PERF_DOMAIN_ARTIFICIAL is set for such
platform. Special care should be taken by other frameworks which are using EM
to test and treat this flag properly.
Registration of 'simple' EM
~~~~~~~~~~~~~~~~~~~~~~~~~~~