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.