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1.. SPDX-License-Identifier: GPL-2.02.. include:: <isonum.txt>3 4======================================5Intel Performance and Energy Bias Hint6======================================7 8:Copyright: |copy| 2019 Intel Corporation9 10:Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>11 12 13.. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c14 :doc: overview15 16Intel Performance and Energy Bias Attribute in ``sysfs``17========================================================18 19The Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU20can be checked or updated through a ``sysfs`` attribute (file) under21:file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>``22is allocated at the system initialization time:23 24``energy_perf_bias``25 Shows the current EPB value for the CPU in a sliding scale 0 - 15, where26 a value of 0 corresponds to a hint preference for highest performance27 and a value of 15 corresponds to the maximum energy savings.28 29 In order to update the EPB value for the CPU, this attribute can be30 written to, either with a number in the 0 - 15 sliding scale above, or31 with one of the strings: "performance", "balance-performance", "normal",32 "balance-power", "power" that represent values reflected by their33 meaning.34 35 This attribute is present for all online CPUs supporting the EPB36 feature.37 38Note that while the EPB interface to the processor is defined at the logical CPU39level, the physical register backing it may be shared by multiple CPUs (for40example, SMT siblings or cores in one package). For this reason, updating the41EPB value for one CPU may cause the EPB values for other CPUs to change.42