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diff --git a/Documentation/hwmon/amd_energy.rst b/Documentation/hwmon/amd_energy.rst new file mode 100644 index 000000000..86e4ebc5c --- /dev/null +++ b/Documentation/hwmon/amd_energy.rst @@ -0,0 +1,114 @@ +.. SPDX-License-Identifier: GPL-2.0 + +Kernel driver amd_energy +========================== + +Supported chips: + +* AMD Family 17h Processors + + Prefix: 'amd_energy' + + Addresses used: RAPL MSRs + + Datasheets: + + - Processor Programming Reference (PPR) for AMD Family 17h Model 01h, Revision B1 Processors + + https://developer.amd.com/wp-content/resources/55570-B1_PUB.zip + + - Preliminary Processor Programming Reference (PPR) for AMD Family 17h Model 31h, Revision B0 Processors + + https://developer.amd.com/wp-content/resources/56176_ppr_Family_17h_Model_71h_B0_pub_Rev_3.06.zip + +Author: Naveen Krishna Chatradhi <nchatrad@amd.com> + +Description +----------- + +The Energy driver exposes the energy counters that are +reported via the Running Average Power Limit (RAPL) +Model-specific Registers (MSRs) via the hardware monitor +(HWMON) sysfs interface. + +1. Power, Energy and Time Units + MSR_RAPL_POWER_UNIT/ C001_0299: + shared with all cores in the socket + +2. Energy consumed by each Core + MSR_CORE_ENERGY_STATUS/ C001_029A: + 32-bitRO, Accumulator, core-level power reporting + +3. Energy consumed by Socket + MSR_PACKAGE_ENERGY_STATUS/ C001_029B: + 32-bitRO, Accumulator, socket-level power reporting, + shared with all cores in socket + +These registers are updated every 1ms and cleared on +reset of the system. + +Note: If SMT is enabled, Linux enumerates all threads as cpus. +Since, the energy status registers are accessed at core level, +reading those registers from the sibling threads would result +in duplicate values. Hence, energy counter entries are not +populated for the siblings. + +Energy Caluclation +------------------ + +Energy information (in Joules) is based on the multiplier, +1/2^ESU; where ESU is an unsigned integer read from +MSR_RAPL_POWER_UNIT register. Default value is 10000b, +indicating energy status unit is 15.3 micro-Joules increment. + +Reported values are scaled as per the formula + +scaled value = ((1/2^ESU) * (Raw value) * 1000000UL) in uJoules + +Users calculate power for a given domain by calculating + dEnergy/dTime for that domain. + +Energy accumulation +-------------------------- + +Current, Socket energy status register is 32bit, assuming a 240W +2P system, the register would wrap around in + + 2^32*15.3 e-6/240 * 2 = 547.60833024 secs to wrap(~9 mins) + +The Core energy register may wrap around after several days. + +To improve the wrap around time, a kernel thread is implemented +to accumulate the socket energy counters and one core energy counter +per run to a respective 64-bit counter. The kernel thread starts +running during probe, wakes up every 100secs and stops running +when driver is removed. + +Frequency of the accumulator thread is set during the probe +based on the chosen energy unit resolution. For example +A. fine grain (1.625 micro J) +B. course grain (0.125 milli J) + +A socket and core energy read would return the current register +value added to the respective energy accumulator. + +Sysfs attributes +---------------- + +=============== ======== ===================================== +Attribute Label Description +=============== ======== ===================================== + +* For index N between [1] and [nr_cpus] + +=============== ======== ====================================== +energy[N]_input EcoreX Core Energy X = [0] to [nr_cpus - 1] + Measured input core energy +=============== ======== ====================================== + +* For N between [nr_cpus] and [nr_cpus + nr_socks] + +=============== ======== ====================================== +energy[N]_input EsocketX Socket Energy X = [0] to [nr_socks -1] + Measured input socket energy +=============== ======== ====================================== |