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