| .. SPDX-License-Identifier: GPL-2.0 | |
| .. include:: <isonum.txt> | |
| ====================================== | |
| Intel Performance and Energy Bias Hint | |
| ====================================== | |
| :Copyright: |copy| 2019 Intel Corporation | |
| :Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com> | |
| .. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c | |
| :doc: overview | |
| Intel Performance and Energy Bias Attribute in ``sysfs`` | |
| ======================================================== | |
| The Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU | |
| can be checked or updated through a ``sysfs`` attribute (file) under | |
| :file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>`` | |
| is allocated at the system initialization time: | |
| ``energy_perf_bias`` | |
| Shows the current EPB value for the CPU in a sliding scale 0 - 15, where | |
| a value of 0 corresponds to a hint preference for highest performance | |
| and a value of 15 corresponds to the maximum energy savings. | |
| In order to update the EPB value for the CPU, this attribute can be | |
| written to, either with a number in the 0 - 15 sliding scale above, or | |
| with one of the strings: "performance", "balance-performance", "normal", | |
| "balance-power", "power" that represent values reflected by their | |
| meaning. | |
| This attribute is present for all online CPUs supporting the EPB | |
| feature. | |
| Note that while the EPB interface to the processor is defined at the logical CPU | |
| level, the physical register backing it may be shared by multiple CPUs (for | |
| example, SMT siblings or cores in one package). For this reason, updating the | |
| EPB value for one CPU may cause the EPB values for other CPUs to change. |