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0001 .. SPDX-License-Identifier: GPL-2.0
0002 .. include:: <isonum.txt>
0003 
0004 ======================================
0005 Intel Performance and Energy Bias Hint
0006 ======================================
0007 
0008 :Copyright: |copy| 2019 Intel Corporation
0009 
0010 :Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
0011 
0012 
0013 .. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c
0014    :doc: overview
0015 
0016 Intel Performance and Energy Bias Attribute in ``sysfs``
0017 ========================================================
0018 
0019 The Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU
0020 can be checked or updated through a ``sysfs`` attribute (file) under
0021 :file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>``
0022 is allocated at the system initialization time:
0023 
0024 ``energy_perf_bias``
0025         Shows the current EPB value for the CPU in a sliding scale 0 - 15, where
0026         a value of 0 corresponds to a hint preference for highest performance
0027         and a value of 15 corresponds to the maximum energy savings.
0028 
0029         In order to update the EPB value for the CPU, this attribute can be
0030         written to, either with a number in the 0 - 15 sliding scale above, or
0031         with one of the strings: "performance", "balance-performance", "normal",
0032         "balance-power", "power" that represent values reflected by their
0033         meaning.
0034 
0035         This attribute is present for all online CPUs supporting the EPB
0036         feature.
0037 
0038 Note that while the EPB interface to the processor is defined at the logical CPU
0039 level, the physical register backing it may be shared by multiple CPUs (for
0040 example, SMT siblings or cores in one package).  For this reason, updating the
0041 EPB value for one CPU may cause the EPB values for other CPUs to change.