1======================= 2Power Capping Framework 3======================= 4 5The power capping framework provides a consistent interface between the kernel 6and the user space that allows power capping drivers to expose the settings to 7user space in a uniform way. 8 9Terminology 10=========== 11 12The framework exposes power capping devices to user space via sysfs in the 13form of a tree of objects. The objects at the root level of the tree represent 14'control types', which correspond to different methods of power capping. For 15example, the intel-rapl control type represents the Intel "Running Average 16Power Limit" (RAPL) technology, whereas the 'idle-injection' control type 17corresponds to the use of idle injection for controlling power. 18 19Power zones represent different parts of the system, which can be controlled and 20monitored using the power capping method determined by the control type the 21given zone belongs to. They each contain attributes for monitoring power, as 22well as controls represented in the form of power constraints. If the parts of 23the system represented by different power zones are hierarchical (that is, one 24bigger part consists of multiple smaller parts that each have their own power 25controls), those power zones may also be organized in a hierarchy with one 26parent power zone containing multiple subzones and so on to reflect the power 27control topology of the system. In that case, it is possible to apply power 28capping to a set of devices together using the parent power zone and if more 29fine grained control is required, it can be applied through the subzones. 30 31 32Example sysfs interface tree:: 33 34 /sys/devices/virtual/powercap 35 └──intel-rapl 36 ├──intel-rapl:0 37 │ ├──constraint_0_name 38 │ ├──constraint_0_power_limit_uw 39 │ ├──constraint_0_time_window_us 40 │ ├──constraint_1_name 41 │ ├──constraint_1_power_limit_uw 42 │ ├──constraint_1_time_window_us 43 │ ├──device -> ../../intel-rapl 44 │ ├──energy_uj 45 │ ├──intel-rapl:0:0 46 │ │ ├──constraint_0_name 47 │ │ ├──constraint_0_power_limit_uw 48 │ │ ├──constraint_0_time_window_us 49 │ │ ├──constraint_1_name 50 │ │ ├──constraint_1_power_limit_uw 51 │ │ ├──constraint_1_time_window_us 52 │ │ ├──device -> ../../intel-rapl:0 53 │ │ ├──energy_uj 54 │ │ ├──max_energy_range_uj 55 │ │ ├──name 56 │ │ ├──enabled 57 │ │ ├──power 58 │ │ │ ├──async 59 │ │ │ [] 60 │ │ ├──subsystem -> ../../../../../../class/power_cap 61 │ │ └──uevent 62 │ ├──intel-rapl:0:1 63 │ │ ├──constraint_0_name 64 │ │ ├──constraint_0_power_limit_uw 65 │ │ ├──constraint_0_time_window_us 66 │ │ ├──constraint_1_name 67 │ │ ├──constraint_1_power_limit_uw 68 │ │ ├──constraint_1_time_window_us 69 │ │ ├──device -> ../../intel-rapl:0 70 │ │ ├──energy_uj 71 │ │ ├──max_energy_range_uj 72 │ │ ├──name 73 │ │ ├──enabled 74 │ │ ├──power 75 │ │ │ ├──async 76 │ │ │ [] 77 │ │ ├──subsystem -> ../../../../../../class/power_cap 78 │ │ └──uevent 79 │ ├──max_energy_range_uj 80 │ ├──max_power_range_uw 81 │ ├──name 82 │ ├──enabled 83 │ ├──power 84 │ │ ├──async 85 │ │ [] 86 │ ├──subsystem -> ../../../../../class/power_cap 87 │ ├──enabled 88 │ ├──uevent 89 ├──intel-rapl:1 90 │ ├──constraint_0_name 91 │ ├──constraint_0_power_limit_uw 92 │ ├──constraint_0_time_window_us 93 │ ├──constraint_1_name 94 │ ├──constraint_1_power_limit_uw 95 │ ├──constraint_1_time_window_us 96 │ ├──device -> ../../intel-rapl 97 │ ├──energy_uj 98 │ ├──intel-rapl:1:0 99 │ │ ├──constraint_0_name 100 │ │ ├──constraint_0_power_limit_uw 101 │ │ ├──constraint_0_time_window_us 102 │ │ ├──constraint_1_name 103 │ │ ├──constraint_1_power_limit_uw 104 │ │ ├──constraint_1_time_window_us 105 │ │ ├──device -> ../../intel-rapl:1 106 │ │ ├──energy_uj 107 │ │ ├──max_energy_range_uj 108 │ │ ├──name 109 │ │ ├──enabled 110 │ │ ├──power 111 │ │ │ ├──async 112 │ │ │ [] 113 │ │ ├──subsystem -> ../../../../../../class/power_cap 114 │ │ └──uevent 115 │ ├──intel-rapl:1:1 116 │ │ ├──constraint_0_name 117 │ │ ├──constraint_0_power_limit_uw 118 │ │ ├──constraint_0_time_window_us 119 │ │ ├──constraint_1_name 120 │ │ ├──constraint_1_power_limit_uw 121 │ │ ├──constraint_1_time_window_us 122 │ │ ├──device -> ../../intel-rapl:1 123 │ │ ├──energy_uj 124 │ │ ├──max_energy_range_uj 125 │ │ ├──name 126 │ │ ├──enabled 127 │ │ ├──power 128 │ │ │ ├──async 129 │ │ │ [] 130 │ │ ├──subsystem -> ../../../../../../class/power_cap 131 │ │ └──uevent 132 │ ├──max_energy_range_uj 133 │ ├──max_power_range_uw 134 │ ├──name 135 │ ├──enabled 136 │ ├──power 137 │ │ ├──async 138 │ │ [] 139 │ ├──subsystem -> ../../../../../class/power_cap 140 │ ├──uevent 141 ├──power 142 │ ├──async 143 │ [] 144 ├──subsystem -> ../../../../class/power_cap 145 ├──enabled 146 └──uevent 147 148The above example illustrates a case in which the Intel RAPL technology, 149available in Intel® IA-64 and IA-32 Processor Architectures, is used. There is one 150control type called intel-rapl which contains two power zones, intel-rapl:0 and 151intel-rapl:1, representing CPU packages. Each of these power zones contains 152two subzones, intel-rapl:j:0 and intel-rapl:j:1 (j = 0, 1), representing the 153"core" and the "uncore" parts of the given CPU package, respectively. All of 154the zones and subzones contain energy monitoring attributes (energy_uj, 155max_energy_range_uj) and constraint attributes (constraint_*) allowing controls 156to be applied (the constraints in the 'package' power zones apply to the whole 157CPU packages and the subzone constraints only apply to the respective parts of 158the given package individually). Since Intel RAPL doesn't provide instantaneous 159power value, there is no power_uw attribute. 160 161In addition to that, each power zone contains a name attribute, allowing the 162part of the system represented by that zone to be identified. 163For example:: 164 165 cat /sys/class/power_cap/intel-rapl/intel-rapl:0/name 166 167package-0 168--------- 169 170Depending on different power zones, the Intel RAPL technology allows 171one or multiple constraints like short term, long term and peak power, 172with different time windows to be applied to each power zone. 173All the zones contain attributes representing the constraint names, 174power limits and the sizes of the time windows. Note that time window 175is not applicable to peak power. Here, constraint_j_* attributes 176correspond to the jth constraint (j = 0,1,2). 177 178For example:: 179 180 constraint_0_name 181 constraint_0_power_limit_uw 182 constraint_0_time_window_us 183 constraint_1_name 184 constraint_1_power_limit_uw 185 constraint_1_time_window_us 186 constraint_2_name 187 constraint_2_power_limit_uw 188 constraint_2_time_window_us 189 190Power Zone Attributes 191===================== 192 193Monitoring attributes 194--------------------- 195 196energy_uj (rw) 197 Current energy counter in micro joules. Write "0" to reset. 198 If the counter can not be reset, then this attribute is read only. 199 200max_energy_range_uj (ro) 201 Range of the above energy counter in micro-joules. 202 203power_uw (ro) 204 Current power in micro watts. 205 206max_power_range_uw (ro) 207 Range of the above power value in micro-watts. 208 209name (ro) 210 Name of this power zone. 211 212It is possible that some domains have both power ranges and energy counter ranges; 213however, only one is mandatory. 214 215Constraints 216----------- 217 218constraint_X_power_limit_uw (rw) 219 Power limit in micro watts, which should be applicable for the 220 time window specified by "constraint_X_time_window_us". 221 222constraint_X_time_window_us (rw) 223 Time window in micro seconds. 224 225constraint_X_name (ro) 226 An optional name of the constraint 227 228constraint_X_max_power_uw(ro) 229 Maximum allowed power in micro watts. 230 231constraint_X_min_power_uw(ro) 232 Minimum allowed power in micro watts. 233 234constraint_X_max_time_window_us(ro) 235 Maximum allowed time window in micro seconds. 236 237constraint_X_min_time_window_us(ro) 238 Minimum allowed time window in micro seconds. 239 240Except power_limit_uw and time_window_us other fields are optional. 241 242Common zone and control type attributes 243--------------------------------------- 244 245enabled (rw): Enable/Disable controls at zone level or for all zones using 246a control type. 247 248Power Cap Client Driver Interface 249================================= 250 251The API summary: 252 253Call powercap_register_control_type() to register control type object. 254Call powercap_register_zone() to register a power zone (under a given 255control type), either as a top-level power zone or as a subzone of another 256power zone registered earlier. 257The number of constraints in a power zone and the corresponding callbacks have 258to be defined prior to calling powercap_register_zone() to register that zone. 259 260To Free a power zone call powercap_unregister_zone(). 261To free a control type object call powercap_unregister_control_type(). 262Detailed API can be generated using kernel-doc on include/linux/powercap.h. 263