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