intel_epb.rst (1647B)
1.. SPDX-License-Identifier: GPL-2.0 2.. include:: <isonum.txt> 3 4====================================== 5Intel 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 16Intel Performance and Energy Bias Attribute in ``sysfs`` 17======================================================== 18 19The Intel Performance and Energy Bias Hint (EPB) value for a given (logical) CPU 20can be checked or updated through a ``sysfs`` attribute (file) under 21:file:`/sys/devices/system/cpu/cpu<N>/power/`, where the CPU number ``<N>`` 22is 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 38Note that while the EPB interface to the processor is defined at the logical CPU 39level, the physical register backing it may be shared by multiple CPUs (for 40example, SMT siblings or cores in one package). For this reason, updating the 41EPB value for one CPU may cause the EPB values for other CPUs to change.