120 lines
3.7 KiB
ReStructuredText
120 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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Kernel driver amd_energy
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==========================
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Supported chips:
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* AMD Family 17h Processors: Model 30h
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* AMD Family 19h Processors: Model 01h
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Prefix: 'amd_energy'
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Addresses used: RAPL MSRs
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Datasheets:
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- Processor Programming Reference (PPR) for AMD Family 17h Model 01h, Revision B1 Processors
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https://developer.amd.com/wp-content/resources/55570-B1_PUB.zip
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- Preliminary Processor Programming Reference (PPR) for AMD Family 17h Model 31h, Revision B0 Processors
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https://developer.amd.com/wp-content/resources/56176_ppr_Family_17h_Model_71h_B0_pub_Rev_3.06.zip
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Author: Naveen Krishna Chatradhi <nchatrad@amd.com>
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Description
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-----------
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The Energy driver exposes the energy counters that are
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reported via the Running Average Power Limit (RAPL)
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Model-specific Registers (MSRs) via the hardware monitor
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(HWMON) sysfs interface.
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1. Power, Energy and Time Units
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MSR_RAPL_POWER_UNIT/ C001_0299:
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shared with all cores in the socket
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2. Energy consumed by each Core
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MSR_CORE_ENERGY_STATUS/ C001_029A:
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32-bitRO, Accumulator, core-level power reporting
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3. Energy consumed by Socket
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MSR_PACKAGE_ENERGY_STATUS/ C001_029B:
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32-bitRO, Accumulator, socket-level power reporting,
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shared with all cores in socket
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These registers are updated every 1ms and cleared on
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reset of the system.
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Note: If SMT is enabled, Linux enumerates all threads as cpus.
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Since, the energy status registers are accessed at core level,
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reading those registers from the sibling threads would result
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in duplicate values. Hence, energy counter entries are not
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populated for the siblings.
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Energy Caluclation
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------------------
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Energy information (in Joules) is based on the multiplier,
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1/2^ESU; where ESU is an unsigned integer read from
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MSR_RAPL_POWER_UNIT register. Default value is 10000b,
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indicating energy status unit is 15.3 micro-Joules increment.
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Reported values are scaled as per the formula
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scaled value = ((1/2^ESU) * (Raw value) * 1000000UL) in uJoules
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Users calculate power for a given domain by calculating
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dEnergy/dTime for that domain.
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Energy accumulation
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--------------------------
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Current, Socket energy status register is 32bit, assuming a 240W
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2P system, the register would wrap around in
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2^32*15.3 e-6/240 * 2 = 547.60833024 secs to wrap(~9 mins)
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The Core energy register may wrap around after several days.
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To improve the wrap around time, a kernel thread is implemented
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to accumulate the socket energy counters and one core energy counter
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per run to a respective 64-bit counter. The kernel thread starts
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running during probe, wakes up every 100secs and stops running
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when driver is removed.
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Frequency of the accumulator thread is set during the probe
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based on the chosen energy unit resolution. For example
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A. fine grain (1.625 micro J)
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B. course grain (0.125 milli J)
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A socket and core energy read would return the current register
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value added to the respective energy accumulator.
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Sysfs attributes
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----------------
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=============== ======== =====================================
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Attribute Label Description
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=============== ======== =====================================
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* For index N between [1] and [nr_cpus]
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=============== ======== ======================================
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energy[N]_input EcoreX Core Energy X = [0] to [nr_cpus - 1]
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Measured input core energy
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=============== ======== ======================================
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* For N between [nr_cpus] and [nr_cpus + nr_socks]
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=============== ======== ======================================
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energy[N]_input EsocketX Socket Energy X = [0] to [nr_socks -1]
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Measured input socket energy
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=============== ======== ======================================
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Note: To address CVE-2020-12912, the visibility of the energy[N]_input
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attributes is restricted to owner and groups only.
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