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Documentation: EM: Switch to micro-Watts scale

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The EM now uses the micro-Watts scale for the power values. Update
related documentation to reflect that fact.

Fix also a problematic sentence in the doc "to:" which triggers test
scripts complaining about wrong email address.

Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Lukasz Luba 2022-07-07 08:15:53 +01:00 committed by Rafael J. Wysocki
parent ae6ccaa650
commit c5d39fae89
1 changed files with 7 additions and 7 deletions
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14
Documentation/power/energy-model.rst
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@ -20,20 +20,20 @@ possible source of information on its own, the EM framework intervenes as an
abstraction layer which standardizes the format of power cost tables in the
kernel, hence enabling to avoid redundant work.
The power values might be expressed in milli-Watts or in an 'abstract scale'.
The power values might be expressed in micro-Watts or in an 'abstract scale'.
Multiple subsystems might use the EM and it is up to the system integrator to
check that the requirements for the power value scale types are met. An example
can be found in the Energy-Aware Scheduler documentation
Documentation/scheduler/sched-energy.rst. For some subsystems like thermal or
powercap power values expressed in an 'abstract scale' might cause issues.
These subsystems are more interested in estimation of power used in the past,
thus the real milli-Watts might be needed. An example of these requirements can
thus the real micro-Watts might be needed. An example of these requirements can
be found in the Intelligent Power Allocation in
Documentation/driver-api/thermal/power_allocator.rst.
Kernel subsystems might implement automatic detection to check whether EM
registered devices have inconsistent scale (based on EM internal flag).
Important thing to keep in mind is that when the power values are expressed in
an 'abstract scale' deriving real energy in milli-Joules would not be possible.
an 'abstract scale' deriving real energy in micro-Joules would not be possible.
The figure below depicts an example of drivers (Arm-specific here, but the
approach is applicable to any architecture) providing power costs to the EM
@ -98,7 +98,7 @@ Drivers are expected to register performance domains into the EM framework by
calling the following API::
int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
struct em_data_callback *cb, cpumask_t *cpus, bool milliwatts);
struct em_data_callback *cb, cpumask_t *cpus, bool microwatts);
Drivers must provide a callback function returning <frequency, power> tuples
for each performance state. The callback function provided by the driver is free
@ -106,10 +106,10 @@ to fetch data from any relevant location (DT, firmware, ...), and by any mean
deemed necessary. Only for CPU devices, drivers must specify the CPUs of the
performance domains using cpumask. For other devices than CPUs the last
argument must be set to NULL.
The last argument 'milliwatts' is important to set with correct value. Kernel
The last argument 'microwatts' is important to set with correct value. Kernel
subsystems which use EM might rely on this flag to check if all EM devices use
the same scale. If there are different scales, these subsystems might decide
to: return warning/error, stop working or panic.
to return warning/error, stop working or panic.
See Section 3. for an example of driver implementing this
callback, or Section 2.4 for further documentation on this API
@ -137,7 +137,7 @@ 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
driver must set the flag 'microwatts' 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