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- .. 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.
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