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diff --git a/Documentation/power/powercap/powercap.rst b/Documentation/power/powercap/powercap.rst new file mode 100644 index 000000000000..7ae3b44c7624 --- /dev/null +++ b/Documentation/power/powercap/powercap.rst @@ -0,0 +1,257 @@ +======================= +Power Capping Framework +======================= + +The power capping framework provides a consistent interface between the kernel +and the user space that allows power capping drivers to expose the settings to +user space in a uniform way. + +Terminology +=========== + +The framework exposes power capping devices to user space via sysfs in the +form of a tree of objects. The objects at the root level of the tree represent +'control types', which correspond to different methods of power capping. For +example, the intel-rapl control type represents the Intel "Running Average +Power Limit" (RAPL) technology, whereas the 'idle-injection' control type +corresponds to the use of idle injection for controlling power. + +Power zones represent different parts of the system, which can be controlled and +monitored using the power capping method determined by the control type the +given zone belongs to. They each contain attributes for monitoring power, as +well as controls represented in the form of power constraints. If the parts of +the system represented by different power zones are hierarchical (that is, one +bigger part consists of multiple smaller parts that each have their own power +controls), those power zones may also be organized in a hierarchy with one +parent power zone containing multiple subzones and so on to reflect the power +control topology of the system. In that case, it is possible to apply power +capping to a set of devices together using the parent power zone and if more +fine grained control is required, it can be applied through the subzones. + + +Example sysfs interface tree:: + + /sys/devices/virtual/powercap + └──intel-rapl + ├──intel-rapl:0 + │ ├──constraint_0_name + │ ├──constraint_0_power_limit_uw + │ ├──constraint_0_time_window_us + │ ├──constraint_1_name + │ ├──constraint_1_power_limit_uw + │ ├──constraint_1_time_window_us + │ ├──device -> ../../intel-rapl + │ ├──energy_uj + │ ├──intel-rapl:0:0 + │ │ ├──constraint_0_name + │ │ ├──constraint_0_power_limit_uw + │ │ ├──constraint_0_time_window_us + │ │ ├──constraint_1_name + │ │ ├──constraint_1_power_limit_uw + │ │ ├──constraint_1_time_window_us + │ │ ├──device -> ../../intel-rapl:0 + │ │ ├──energy_uj + │ │ ├──max_energy_range_uj + │ │ ├──name + │ │ ├──enabled + │ │ ├──power + │ │ │ ├──async + │ │ │ [] + │ │ ├──subsystem -> ../../../../../../class/power_cap + │ │ └──uevent + │ ├──intel-rapl:0:1 + │ │ ├──constraint_0_name + │ │ ├──constraint_0_power_limit_uw + │ │ ├──constraint_0_time_window_us + │ │ ├──constraint_1_name + │ │ ├──constraint_1_power_limit_uw + │ │ ├──constraint_1_time_window_us + │ │ ├──device -> ../../intel-rapl:0 + │ │ ├──energy_uj + │ │ ├──max_energy_range_uj + │ │ ├──name + │ │ ├──enabled + │ │ ├──power + │ │ │ ├──async + │ │ │ [] + │ │ ├──subsystem -> ../../../../../../class/power_cap + │ │ └──uevent + │ ├──max_energy_range_uj + │ ├──max_power_range_uw + │ ├──name + │ ├──enabled + │ ├──power + │ │ ├──async + │ │ [] + │ ├──subsystem -> ../../../../../class/power_cap + │ ├──enabled + │ ├──uevent + ├──intel-rapl:1 + │ ├──constraint_0_name + │ ├──constraint_0_power_limit_uw + │ ├──constraint_0_time_window_us + │ ├──constraint_1_name + │ ├──constraint_1_power_limit_uw + │ ├──constraint_1_time_window_us + │ ├──device -> ../../intel-rapl + │ ├──energy_uj + │ ├──intel-rapl:1:0 + │ │ ├──constraint_0_name + │ │ ├──constraint_0_power_limit_uw + │ │ ├──constraint_0_time_window_us + │ │ ├──constraint_1_name + │ │ ├──constraint_1_power_limit_uw + │ │ ├──constraint_1_time_window_us + │ │ ├──device -> ../../intel-rapl:1 + │ │ ├──energy_uj + │ │ ├──max_energy_range_uj + │ │ ├──name + │ │ ├──enabled + │ │ ├──power + │ │ │ ├──async + │ │ │ [] + │ │ ├──subsystem -> ../../../../../../class/power_cap + │ │ └──uevent + │ ├──intel-rapl:1:1 + │ │ ├──constraint_0_name + │ │ ├──constraint_0_power_limit_uw + │ │ ├──constraint_0_time_window_us + │ │ ├──constraint_1_name + │ │ ├──constraint_1_power_limit_uw + │ │ ├──constraint_1_time_window_us + │ │ ├──device -> ../../intel-rapl:1 + │ │ ├──energy_uj + │ │ ├──max_energy_range_uj + │ │ ├──name + │ │ ├──enabled + │ │ ├──power + │ │ │ ├──async + │ │ │ [] + │ │ ├──subsystem -> ../../../../../../class/power_cap + │ │ └──uevent + │ ├──max_energy_range_uj + │ ├──max_power_range_uw + │ ├──name + │ ├──enabled + │ ├──power + │ │ ├──async + │ │ [] + │ ├──subsystem -> ../../../../../class/power_cap + │ ├──uevent + ├──power + │ ├──async + │ [] + ├──subsystem -> ../../../../class/power_cap + ├──enabled + └──uevent + +The above example illustrates a case in which the Intel RAPL technology, +available in Intel® IA-64 and IA-32 Processor Architectures, is used. There is one +control type called intel-rapl which contains two power zones, intel-rapl:0 and +intel-rapl:1, representing CPU packages. Each of these power zones contains +two subzones, intel-rapl:j:0 and intel-rapl:j:1 (j = 0, 1), representing the +"core" and the "uncore" parts of the given CPU package, respectively. All of +the zones and subzones contain energy monitoring attributes (energy_uj, +max_energy_range_uj) and constraint attributes (constraint_*) allowing controls +to be applied (the constraints in the 'package' power zones apply to the whole +CPU packages and the subzone constraints only apply to the respective parts of +the given package individually). Since Intel RAPL doesn't provide instantaneous +power value, there is no power_uw attribute. + +In addition to that, each power zone contains a name attribute, allowing the +part of the system represented by that zone to be identified. +For example:: + + cat /sys/class/power_cap/intel-rapl/intel-rapl:0/name + +package-0 +--------- + +The Intel RAPL technology allows two constraints, short term and long term, +with two different time windows to be applied to each power zone. Thus for +each zone there are 2 attributes representing the constraint names, 2 power +limits and 2 attributes representing the sizes of the time windows. Such that, +constraint_j_* attributes correspond to the jth constraint (j = 0,1). + +For example:: + + constraint_0_name + constraint_0_power_limit_uw + constraint_0_time_window_us + constraint_1_name + constraint_1_power_limit_uw + constraint_1_time_window_us + +Power Zone Attributes +===================== + +Monitoring attributes +--------------------- + +energy_uj (rw) + Current energy counter in micro joules. Write "0" to reset. + If the counter can not be reset, then this attribute is read only. + +max_energy_range_uj (ro) + Range of the above energy counter in micro-joules. + +power_uw (ro) + Current power in micro watts. + +max_power_range_uw (ro) + Range of the above power value in micro-watts. + +name (ro) + Name of this power zone. + +It is possible that some domains have both power ranges and energy counter ranges; +however, only one is mandatory. + +Constraints +----------- + +constraint_X_power_limit_uw (rw) + Power limit in micro watts, which should be applicable for the + time window specified by "constraint_X_time_window_us". + +constraint_X_time_window_us (rw) + Time window in micro seconds. + +constraint_X_name (ro) + An optional name of the constraint + +constraint_X_max_power_uw(ro) + Maximum allowed power in micro watts. + +constraint_X_min_power_uw(ro) + Minimum allowed power in micro watts. + +constraint_X_max_time_window_us(ro) + Maximum allowed time window in micro seconds. + +constraint_X_min_time_window_us(ro) + Minimum allowed time window in micro seconds. + +Except power_limit_uw and time_window_us other fields are optional. + +Common zone and control type attributes +--------------------------------------- + +enabled (rw): Enable/Disable controls at zone level or for all zones using +a control type. + +Power Cap Client Driver Interface +================================= + +The API summary: + +Call powercap_register_control_type() to register control type object. +Call powercap_register_zone() to register a power zone (under a given +control type), either as a top-level power zone or as a subzone of another +power zone registered earlier. +The number of constraints in a power zone and the corresponding callbacks have +to be defined prior to calling powercap_register_zone() to register that zone. + +To Free a power zone call powercap_unregister_zone(). +To free a control type object call powercap_unregister_control_type(). +Detailed API can be generated using kernel-doc on include/linux/powercap.h. |