258 lines
10 KiB
ReStructuredText
258 lines
10 KiB
ReStructuredText
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=======================
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Power Capping Framework
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=======================
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The power capping framework provides a consistent interface between the kernel
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and the user space that allows power capping drivers to expose the settings to
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user space in a uniform way.
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Terminology
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===========
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The framework exposes power capping devices to user space via sysfs in the
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form of a tree of objects. The objects at the root level of the tree represent
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'control types', which correspond to different methods of power capping. For
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example, the intel-rapl control type represents the Intel "Running Average
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Power Limit" (RAPL) technology, whereas the 'idle-injection' control type
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corresponds to the use of idle injection for controlling power.
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Power zones represent different parts of the system, which can be controlled and
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monitored using the power capping method determined by the control type the
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given zone belongs to. They each contain attributes for monitoring power, as
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well as controls represented in the form of power constraints. If the parts of
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the system represented by different power zones are hierarchical (that is, one
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bigger part consists of multiple smaller parts that each have their own power
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controls), those power zones may also be organized in a hierarchy with one
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parent power zone containing multiple subzones and so on to reflect the power
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control topology of the system. In that case, it is possible to apply power
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capping to a set of devices together using the parent power zone and if more
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fine grained control is required, it can be applied through the subzones.
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Example sysfs interface tree::
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/sys/devices/virtual/powercap
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└──intel-rapl
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├──intel-rapl:0
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│ ├──constraint_0_name
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│ ├──constraint_0_power_limit_uw
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│ ├──constraint_0_time_window_us
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│ ├──constraint_1_name
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│ ├──constraint_1_power_limit_uw
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│ ├──constraint_1_time_window_us
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│ ├──device -> ../../intel-rapl
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│ ├──energy_uj
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│ ├──intel-rapl:0:0
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│ │ ├──constraint_0_name
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│ │ ├──constraint_0_power_limit_uw
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│ │ ├──constraint_0_time_window_us
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│ │ ├──constraint_1_name
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│ │ ├──constraint_1_power_limit_uw
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│ │ ├──constraint_1_time_window_us
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│ │ ├──device -> ../../intel-rapl:0
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│ │ ├──energy_uj
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│ │ ├──max_energy_range_uj
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│ │ ├──name
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│ │ ├──enabled
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│ │ ├──power
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│ │ │ ├──async
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│ │ │ []
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│ │ ├──subsystem -> ../../../../../../class/power_cap
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│ │ └──uevent
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│ ├──intel-rapl:0:1
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│ │ ├──constraint_0_name
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│ │ ├──constraint_0_power_limit_uw
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│ │ ├──constraint_0_time_window_us
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│ │ ├──constraint_1_name
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│ │ ├──constraint_1_power_limit_uw
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│ │ ├──constraint_1_time_window_us
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│ │ ├──device -> ../../intel-rapl:0
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│ │ ├──energy_uj
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│ │ ├──max_energy_range_uj
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│ │ ├──name
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│ │ ├──enabled
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│ │ ├──power
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│ │ │ ├──async
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│ │ │ []
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│ │ ├──subsystem -> ../../../../../../class/power_cap
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│ │ └──uevent
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│ ├──max_energy_range_uj
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│ ├──max_power_range_uw
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│ ├──name
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│ ├──enabled
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│ ├──power
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│ │ ├──async
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│ │ []
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│ ├──subsystem -> ../../../../../class/power_cap
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│ ├──enabled
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│ ├──uevent
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├──intel-rapl:1
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│ ├──constraint_0_name
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│ ├──constraint_0_power_limit_uw
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│ ├──constraint_0_time_window_us
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│ ├──constraint_1_name
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│ ├──constraint_1_power_limit_uw
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│ ├──constraint_1_time_window_us
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│ ├──device -> ../../intel-rapl
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│ ├──energy_uj
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│ ├──intel-rapl:1:0
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│ │ ├──constraint_0_name
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│ │ ├──constraint_0_power_limit_uw
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│ │ ├──constraint_0_time_window_us
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│ │ ├──constraint_1_name
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│ │ ├──constraint_1_power_limit_uw
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│ │ ├──constraint_1_time_window_us
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│ │ ├──device -> ../../intel-rapl:1
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│ │ ├──energy_uj
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│ │ ├──max_energy_range_uj
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│ │ ├──name
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│ │ ├──enabled
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│ │ ├──power
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│ │ │ ├──async
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│ │ │ []
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│ │ ├──subsystem -> ../../../../../../class/power_cap
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│ │ └──uevent
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│ ├──intel-rapl:1:1
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│ │ ├──constraint_0_name
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│ │ ├──constraint_0_power_limit_uw
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│ │ ├──constraint_0_time_window_us
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│ │ ├──constraint_1_name
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│ │ ├──constraint_1_power_limit_uw
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│ │ ├──constraint_1_time_window_us
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│ │ ├──device -> ../../intel-rapl:1
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│ │ ├──energy_uj
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│ │ ├──max_energy_range_uj
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│ │ ├──name
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│ │ ├──enabled
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│ │ ├──power
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│ │ │ ├──async
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│ │ │ []
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│ │ ├──subsystem -> ../../../../../../class/power_cap
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│ │ └──uevent
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│ ├──max_energy_range_uj
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│ ├──max_power_range_uw
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│ ├──name
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│ ├──enabled
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│ ├──power
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│ │ ├──async
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│ │ []
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│ ├──subsystem -> ../../../../../class/power_cap
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│ ├──uevent
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├──power
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│ ├──async
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│ []
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├──subsystem -> ../../../../class/power_cap
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├──enabled
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└──uevent
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The above example illustrates a case in which the Intel RAPL technology,
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available in Intel® IA-64 and IA-32 Processor Architectures, is used. There is one
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control type called intel-rapl which contains two power zones, intel-rapl:0 and
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intel-rapl:1, representing CPU packages. Each of these power zones contains
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two subzones, intel-rapl:j:0 and intel-rapl:j:1 (j = 0, 1), representing the
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"core" and the "uncore" parts of the given CPU package, respectively. All of
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the zones and subzones contain energy monitoring attributes (energy_uj,
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max_energy_range_uj) and constraint attributes (constraint_*) allowing controls
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to be applied (the constraints in the 'package' power zones apply to the whole
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CPU packages and the subzone constraints only apply to the respective parts of
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the given package individually). Since Intel RAPL doesn't provide instantaneous
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power value, there is no power_uw attribute.
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In addition to that, each power zone contains a name attribute, allowing the
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part of the system represented by that zone to be identified.
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For example::
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cat /sys/class/power_cap/intel-rapl/intel-rapl:0/name
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package-0
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---------
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The Intel RAPL technology allows two constraints, short term and long term,
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with two different time windows to be applied to each power zone. Thus for
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each zone there are 2 attributes representing the constraint names, 2 power
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limits and 2 attributes representing the sizes of the time windows. Such that,
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constraint_j_* attributes correspond to the jth constraint (j = 0,1).
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For example::
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constraint_0_name
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constraint_0_power_limit_uw
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constraint_0_time_window_us
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constraint_1_name
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constraint_1_power_limit_uw
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constraint_1_time_window_us
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Power Zone Attributes
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=====================
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Monitoring attributes
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---------------------
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energy_uj (rw)
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Current energy counter in micro joules. Write "0" to reset.
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If the counter can not be reset, then this attribute is read only.
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max_energy_range_uj (ro)
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Range of the above energy counter in micro-joules.
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power_uw (ro)
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Current power in micro watts.
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max_power_range_uw (ro)
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Range of the above power value in micro-watts.
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name (ro)
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Name of this power zone.
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It is possible that some domains have both power ranges and energy counter ranges;
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however, only one is mandatory.
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Constraints
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-----------
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constraint_X_power_limit_uw (rw)
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Power limit in micro watts, which should be applicable for the
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time window specified by "constraint_X_time_window_us".
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constraint_X_time_window_us (rw)
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Time window in micro seconds.
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constraint_X_name (ro)
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An optional name of the constraint
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constraint_X_max_power_uw(ro)
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Maximum allowed power in micro watts.
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constraint_X_min_power_uw(ro)
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Minimum allowed power in micro watts.
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constraint_X_max_time_window_us(ro)
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Maximum allowed time window in micro seconds.
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constraint_X_min_time_window_us(ro)
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Minimum allowed time window in micro seconds.
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Except power_limit_uw and time_window_us other fields are optional.
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Common zone and control type attributes
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---------------------------------------
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enabled (rw): Enable/Disable controls at zone level or for all zones using
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a control type.
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Power Cap Client Driver Interface
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=================================
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The API summary:
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Call powercap_register_control_type() to register control type object.
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Call powercap_register_zone() to register a power zone (under a given
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control type), either as a top-level power zone or as a subzone of another
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power zone registered earlier.
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The number of constraints in a power zone and the corresponding callbacks have
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to be defined prior to calling powercap_register_zone() to register that zone.
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To Free a power zone call powercap_unregister_zone().
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To free a control type object call powercap_unregister_control_type().
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Detailed API can be generated using kernel-doc on include/linux/powercap.h.
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