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diff --git a/Documentation/power/powercap/powercap.txt b/Documentation/power/powercap/powercap.txt new file mode 100644 index 000000000000..1e6ef164e07a --- /dev/null +++ b/Documentation/power/powercap/powercap.txt @@ -0,0 +1,236 @@ +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. |