admin-guide/pm/intel_pstate.rst

16 ``intel_pstate`` is a part of the
18 (``CPUFreq``).  It is a scaling driver for the Sandy Bridge and later
34 practical for ``intel_pstate`` to supply the ``CPUFreq`` core with a table of
48 command line.  However, its configuration can be adjusted via ``sysfs`` to a
60 mode it responds to requests made by a generic ``CPUFreq`` governor implementing
61 a certain performance scaling algorithm.  Which of them will be in effect
84 ``intel_pstate`` is not a counterpart of the generic ``powersave`` governor
113 in this mode.  However, they are not used for running a P-state selection
127 the EPP/EPB to a value different from 0 ("performance") via ``sysfs`` in this
156 CPU scheduler in order to run a P-state selection algorithm, either
210 Then, the driver behaves like a regular ``CPUFreq`` scaling driver.  That is,
212 hardware in order to change the P-state of a CPU (in particular, the
237 different types of processor behavior, above and below a boundary that
242 range".  These names are related to the Turbo Boost technology allowing a
247 Specifically, if software sets the P-state of a CPU core within the turbo range
254 processor generations will take it as a license to use any P-states from the
264 be exceeded if a turbo P-state was used for too long.
268 it to a lower one unless in a thermal stress or a power limit violation
269 situation (a higher P-state may still be used if it is set for another CPU in
285 threshold effectively becomes a configurable value that can be set by the
305 To handle a given processor ``intel_pstate`` requires a number of different
325 For this reason, there is a list of supported processors in ``intel_pstate`` and
404 	to be increased dynamically for a short time whenever a task previously
405 	waiting on I/O is selected to run on a given logical CPU (the purpose
425 		The driver is not functional (it is not registered as a scaling
435 	with a different set of callbacks, so all of its settings (the global
459 ``scaling_cur_freq`` attributes are produced by applying a processor-specific
527     effective performance can be more than the policy limits set on a CPU, if
540 every time before setting a new P-state for a CPU.
573 Energy-Performance Bias (EPB) knob. It is also possible to write a positive
583 or to pin every task potentially sensitive to them to a specific CPU.]
602 On those systems each ``_PSS`` object returns a list of P-states supported by
603 the corresponding CPU which basically is a subset of the P-states range that can
622 For example, if a given governor attempts to select a frequency proportional to
624 (possibly multiplied by a constant), then it will tend to choose P-states below
626 in that case the turbo range corresponds to a small fraction of the frequency
636 a turbo P-state in those lists and there may be a problem with avoiding the
731 ``intel_pstate``.  For example, to check how often the function to set a