admin-guide/pm/intel_pstate.rst

24 For the processors supported by ``intel_pstate``, the P-state concept is broader
27 information about that).  For this reason, the representation of P-states used
32 ``intel_pstate`` maps its internal representation of P-states to frequencies too
38 Since the hardware P-state selection interface used by ``intel_pstate`` is
69 hardware-managed P-states (HWP) support.  If it works in this mode, the
74 provides its own scaling algorithms for P-state selection.  Those algorithms
77 ``sysfs``).  [Note that different P-state selection algorithms may be chosen for
83 For example, the ``powersave`` P-state selection algorithm provided by
87 There are two P-state selection algorithms provided by ``intel_pstate`` in the
89 depends on whether or not the hardware-managed P-states (HWP) feature has been
92 Which of the P-state selection algorithms is used by default depends on the
106 select P-states by itself, but still it can give hints to the processor's
107 internal P-state selection logic.  What those hints are depends on which P-state
111 Even though the P-state selection is carried out by the processor automatically,
113 in this mode.  However, they are not used for running a P-state selection
123 internal P-state selection logic is expected to focus entirely on performance.
130 Also, in this configuration the range of P-states available to the processor's
131 internal P-state selection logic is always restricted to the upper boundary
132 (that is, the maximum P-state that the driver is allowed to use).
142 internal P-state selection logic to be less performance-focused.
156 CPU scheduler in order to run a P-state selection algorithm, either
165 Without HWP, this P-state selection algorithm is always the same regardless of
168 It selects the maximum P-state it is allowed to use, subject to limits set via
172 This is the default P-state selection algorithm if the
179 Without HWP, this P-state selection algorithm is similar to the algorithm
182 registers of the CPU.  It generally selects P-states proportional to the
188 is not touched if the new P-state turns out to be the same as the current
191 This is the default P-state selection algorithm if the
199 hardware-managed P-states (HWP) support.  It is always used if the
212 hardware in order to change the P-state of a CPU (in particular, the
217 in ``sysfs`` (and the P-state selection algorithms described above are not
223 the entire range of available P-states is exposed by ``intel_pstate`` to the
232 Turbo P-states Support
235 In the majority of cases, the entire range of P-states available to
240 The P-states above the turbo threshold are referred to as "turbo P-states" and
241 the whole sub-range of P-states they belong to is referred to as the "turbo
243 multicore processor to opportunistically increase the P-state of one or more
247 Specifically, if software sets the P-state of a CPU core within the turbo range
249 performance scaling control for that core and put it into turbo P-states of its
252 processors will never use any P-states above the last one set by software for
254 processor generations will take it as a license to use any P-states from the
256 processors setting any P-state from the turbo range will enable the processor
257 to put the given core into all turbo P-states up to and including the maximum
260 One important property of turbo P-states is that they are not sustainable.  More
264 be exceeded if a turbo P-state was used for too long.
266 In turn, the P-states below the turbo threshold generally are sustainable.  In
269 situation (a higher P-state may still be used if it is set for another CPU in
272 Some processors allow multiple cores to be in turbo P-states at the same time,
273 but the maximum P-state that can be set for them generally depends on the number
274 of cores running concurrently.  The maximum turbo P-state that can be set for 3
275 cores at the same time usually is lower than the analogous maximum P-state for
276 2 cores, which in turn usually is lower than the maximum turbo P-state that can
277 be set for 1 core.  The one-core maximum turbo P-state is thus the maximum
280 The maximum supported turbo P-state, the turbo threshold (the maximum supported
281 non-turbo P-state) and the minimum supported P-state are specific to the
289 the entire range of available P-states, including the whole turbo range, to the
291 generally causes turbo P-states to be set more often when ``intel_pstate`` is
298 work as expected in all cases (that is, if set to disable turbo P-states, it
308  * The minimum supported P-state.
310  * The maximum supported `non-turbo P-state <turbo_>`_.
312  * Whether or not turbo P-states are supported at all.
314  * The maximum supported `one-core turbo P-state <turbo_>`_ (if turbo P-states
318    of P-states into frequencies and the other way around.
346 	Maximum P-state the driver is allowed to set in percent of the
348 	P-state <turbo_>`_).
355 	Minimum P-state the driver is allowed to set in percent of the
357 	P-state <turbo_>`_).
364 	Number of P-states supported by the processor (between 0 and 255
365 	inclusive) including both turbo and non-turbo P-states (see
366 	`Turbo P-states Support`_).
378 	range of supported P-states, in percent.
388 	If set (equal to 1), the driver is not allowed to set any turbo P-states
389 	(see `Turbo P-states Support`_).  If unset (equal to 0, which is the
390 	default), turbo P-states can be set by the driver.
397 	but it affects the maximum possible value of per-policy P-state	limits
403 	the processor.  If set (equal to 1), it causes the minimum P-state limit
408 	This setting has no effect on logical CPUs whose minimum P-state limit
409 	is directly set to the highest non-turbo P-state or above it.
460 multiplier to the internal P-state representation used by ``intel_pstate``.
462 attributes are capped by the frequency corresponding to the maximum P-state that
466 not allowed to use turbo P-states, so the maximum value of ``scaling_max_freq``
467 and ``scaling_min_freq`` is limited to the maximum non-turbo P-state frequency.
475 and ``scaling_min_freq`` corresponds to the maximum supported turbo P-state,
482 	List of P-state selection algorithms provided by ``intel_pstate``.
485 	P-state selection algorithm provided by ``intel_pstate`` currently in
489 	Frequency of the average P-state of the CPU represented by the given
508 Coordination of P-State Limits
511 ``intel_pstate`` allows P-state limits to be set in two ways: with the help of
525     P-states, hyper-threading is enabled and on current performance requests
526     from other CPUs. When platform doesn't support per core P-states, the
529     core P-states support, when hyper-threading is enabled, if the sibling CPU
537 limits change in order to request its internal P-state selection logic to always
538 set P-states within these limits.  Otherwise, the limits are taken into account
540 every time before setting a new P-state for a CPU.
550 If the hardware-managed P-states (HWP) is enabled in the processor, additional
552 processor's internal P-state selection logic by focusing it on performance or on
599 interface, but the set of P-states it can use is limited by the ``_PSS``
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
607 than the frequency of the highest non-turbo P-state listed by it, but the
608 corresponding P-state representation (following the hardware specification)
609 returned for it matches the maximum supported turbo P-state (or is the
612 The list of P-states returned by ``_PSS`` is reflected by the table of
618 of the highest supported non-turbo P-state listed by ``_PSS`` which, of course,
624 (possibly multiplied by a constant), then it will tend to choose P-states below
629 benefit from running at turbo frequencies will be given non-turbo P-states
634 turbo threshold.  Namely, if that is not coordinated with the lists of P-states
636 a turbo P-state in those lists and there may be a problem with avoiding the
638 P-states overall, ``acpi-cpufreq`` simply avoids using the topmost state listed
639 by ``_PSS``, but that is not sufficient when there are other turbo P-states in
643 `passive mode <Passive Mode_>`_, except that the number of P-states it can set
671 	power capping) that rely on the availability of ACPI P-states
680 	Do not enable the hardware-managed P-states (HWP) feature even if it is
685 	hardware-managed P-states (HWP) feature is supported by the processor.
696 	Use per-logical-CPU P-State limits (see `Coordination of P-state
732 P-state is called, the ``ftrace`` filter can be set to
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