| .. 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. |
