162306a36Sopenharmony_ci.. SPDX-License-Identifier: GPL-2.0 262306a36Sopenharmony_ci.. include:: <isonum.txt> 362306a36Sopenharmony_ci 462306a36Sopenharmony_ci====================================== 562306a36Sopenharmony_ciIntel Performance and Energy Bias Hint 662306a36Sopenharmony_ci====================================== 762306a36Sopenharmony_ci 862306a36Sopenharmony_ci:Copyright: |copy| 2019 Intel Corporation 962306a36Sopenharmony_ci 1062306a36Sopenharmony_ci:Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com> 1162306a36Sopenharmony_ci 1262306a36Sopenharmony_ci 1362306a36Sopenharmony_ci.. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c 1462306a36Sopenharmony_ci :doc: overview 1562306a36Sopenharmony_ci 1662306a36Sopenharmony_ciIntel Performance and Energy Bias Attribute in ``sysfs`` 1762306a36Sopenharmony_ci======================================================== 1862306a36Sopenharmony_ci 1962306a36Sopenharmony_ciThe Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU 2062306a36Sopenharmony_cican be checked or updated through a ``sysfs`` attribute (file) under 2162306a36Sopenharmony_ci:file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>`` 2262306a36Sopenharmony_ciis allocated at the system initialization time: 2362306a36Sopenharmony_ci 2462306a36Sopenharmony_ci``energy_perf_bias`` 2562306a36Sopenharmony_ci Shows the current EPB value for the CPU in a sliding scale 0 - 15, where 2662306a36Sopenharmony_ci a value of 0 corresponds to a hint preference for highest performance 2762306a36Sopenharmony_ci and a value of 15 corresponds to the maximum energy savings. 2862306a36Sopenharmony_ci 2962306a36Sopenharmony_ci In order to update the EPB value for the CPU, this attribute can be 3062306a36Sopenharmony_ci written to, either with a number in the 0 - 15 sliding scale above, or 3162306a36Sopenharmony_ci with one of the strings: "performance", "balance-performance", "normal", 3262306a36Sopenharmony_ci "balance-power", "power" that represent values reflected by their 3362306a36Sopenharmony_ci meaning. 3462306a36Sopenharmony_ci 3562306a36Sopenharmony_ci This attribute is present for all online CPUs supporting the EPB 3662306a36Sopenharmony_ci feature. 3762306a36Sopenharmony_ci 3862306a36Sopenharmony_ciNote that while the EPB interface to the processor is defined at the logical CPU 3962306a36Sopenharmony_cilevel, the physical register backing it may be shared by multiple CPUs (for 4062306a36Sopenharmony_ciexample, SMT siblings or cores in one package). For this reason, updating the 4162306a36Sopenharmony_ciEPB value for one CPU may cause the EPB values for other CPUs to change. 42