1 .. SPDX-License-Identifier: GPL-2.0 2 .. include:: <isonum.txt> 3 4 ====================================== 5 Intel Performance and Energy Bias Hint 6 ====================================== 7 8 :Copyright: |copy| 2019 Intel Corporation 9 10 :Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com> 11 12 13 .. kernel-doc:: arch/x86/kernel/cpu/intel_epb.c 14 :doc: overview 15 16 Intel Performance and Energy Bias Attribute in ``sysfs`` 17 ======================================================== 18 19 The Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU 20 can be checked or updated through a ``sysfs`` attribute (file) under 21 :file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>`` 22 is allocated at the system initialization time: 23 24 ``energy_perf_bias`` 25 Shows the current EPB value for the CPU in a sliding scale 0 - 15, where 26 a value of 0 corresponds to a hint preference for highest performance 27 and a value of 15 corresponds to the maximum energy savings. 28 29 In order to update the EPB value for the CPU, this attribute can be 30 written to, either with a number in the 0 - 15 sliding scale above, or 31 with one of the strings: "performance", "balance-performance", "normal", 32 "balance-power", "power" that represent values reflected by their 33 meaning. 34 35 This attribute is present for all online CPUs supporting the EPB 36 feature. 37 38 Note that while the EPB interface to the processor is defined at the logical CPU 39 level, the physical register backing it may be shared by multiple CPUs (for 40 example, SMT siblings or cores in one package). For this reason, updating the 41 EPB value for one CPU may cause the EPB values for other CPUs to change.
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