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24 For the processors supported by ``intel_pstate``, the P-state concept is broader
26 LinuxCon Europe 2015 presentation by Kristen Accardi [1]_ for more
28 by ``intel_pstate`` internally follows the hardware specification (for details
31 frequencies are involved in the user space interface exposed by it, so
36 that. Some functionality of the core is limited by that.
38 Since the hardware P-state selection interface used by ``intel_pstate`` is
59 allows the hardware to do performance scaling by itself, while in the passive
60 mode it responds to requests made by a generic ``CPUFreq`` governor implementing
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
92 Which of the P-state selection algorithms is used by default depends on the
94 Namely, if that option is set, the ``performance`` algorithm will be used by
95 default, and the other one will be used by default if it is not set.
102 to avoid enabling it by passing the ``intel_pstate=no_hwp`` argument to the
106 select P-states by itself, but still it can give hints to the processor's
111 Even though the P-state selection is carried out by the processor automatically,
141 set to by the platform firmware). This usually causes the processor's
152 recognized by it. [Note that ``intel_pstate`` will never refuse to work with
160 periodically updated by those utilization update callbacks too.
180 implemented by the generic ``schedutil`` scaling governor except that the
181 utilization metric used by it is based on numbers coming from feedback
185 This algorithm is run by the driver's utilization update callback for the
186 given CPU when it is invoked by the CPU scheduler, but not more often than
205 processors that are not recognized by it if HWP is prevented from being enabled
211 it is invoked by generic scaling governors when necessary to talk to the
216 scaling governors listed by the ``scaling_available_governors`` policy attribute
221 maximum and minimum operating frequencies supported by the hardware (including
223 the entire range of available P-states is exposed by ``intel_pstate`` to the
227 by the current scaling governor for the given policy).
250 choice going forward. However, that permission is interpreted differently by
252 processors will never use any P-states above the last one set by software for
255 turbo range, even above the one set by software. In other words, on those
267 fact, if one of them is set by software, the processor is not expected to change
282 processor model and can be determined by reading the processor's model-specific
285 threshold effectively becomes a configurable value that can be set by the
335 Some processors supported by ``intel_pstate`` contain two or more types of CPU
336 cores differing by the maximum turbo P-state, performance vs power characteristics,
369 The capacity-aware scheduling (CAS) support in the CPU scheduler is enabled by
370 ``intel_pstate`` by default on hybrid processors without SMT. CAS generally
388 First of all, the capacity of each CPU is represented by the ratio of its highest
389 HWP performance level, multiplied by 1024, to the highest HWP performance level
392 carried out by the scheduler to always express CPU utilization in the same units
408 The Energy Model registered by ``intel_pstate`` is artificial (that is, it is
427 The Energy Model created by ``intel_pstate`` can be inspected by looking at
464 Number of P-states supported by the processor (between 0 and 255
468 This attribute is present only if the value exposed by it is the same
471 The value of this attribute is not affected by the ``no_turbo``
480 This attribute is present only if the value exposed by it is the same
490 default), turbo P-states can be set by the driver.
492 attribute (supported by some other scaling drivers) which is replaced
493 by this one.]
531 cause the driver to switch over to the operation mode represented by
541 Lake or Coffee Lake desktop CPU model. By default, energy-efficiency
559 ``scaling_cur_freq`` attributes are produced by applying a processor-specific
560 multiplier to the internal P-state representation used by ``intel_pstate``.
562 attributes are capped by the frequency corresponding to the maximum P-state that
582 List of P-state selection algorithms provided by ``intel_pstate``.
585 P-state selection algorithm provided by ``intel_pstate`` currently in
589 Frequency of the average P-state of the CPU represented by the given
591 driver's utilization update callback by the CPU scheduler for that CPU.
617 1. All CPUs are affected by the global limits (that is, none of them can be
621 2. Each individual CPU is affected by its own per-policy limits (that is, it
639 by scaling governors (in the `passive mode <Passive Mode_>`_) and by the driver
644 at all and the only way to set the limits is by using the policy attributes.
652 processor's internal P-state selection logic by focusing it on performance or on
658 (or the CPU represented by it).
660 The hint can be changed by writing to this attribute.
668 value was set by the platform firmware.
679 [Note that tasks may by migrated from one CPU to another by the scheduler's
690 On the majority of systems supported by ``intel_pstate``, the ACPI tables
691 provided by the platform firmware contain ``_PSS`` objects returning information
694 returned by them).
696 The information returned by the ACPI ``_PSS`` objects is used by the
697 ``acpi-cpufreq`` scaling driver. On systems supported by ``intel_pstate``
699 interface, but the set of P-states it can use is limited by the ``_PSS``
702 On those systems each ``_PSS`` object returns a list of P-states supported by
704 be used by ``intel_pstate`` on the same system, with one exception: the whole
705 `turbo range <turbo_>`_ is represented by one item in it (the topmost one). By
706 convention, the frequency returned by ``_PSS`` for that item is greater by 1 MHz
707 than the frequency of the highest non-turbo P-state listed by it, but the
712 The list of P-states returned by ``_PSS`` is reflected by the table of
713 available frequencies supplied by ``acpi-cpufreq`` to the ``CPUFreq`` core and
714 scaling governors and the minimum and maximum supported frequencies reported by
717 frequency reported by ``acpi-cpufreq`` is higher by 1 MHz than the frequency
718 of the highest supported non-turbo P-state listed by ``_PSS`` which, of course,
719 affects decisions made by the scaling governors, except for ``powersave`` and
724 (possibly multiplied by a constant), then it will tend to choose P-states below
735 returned by ``_PSS`` properly, there may be more than one item corresponding to
739 by ``_PSS``, but that is not sufficient when there are other turbo P-states in
740 the list returned by it.
744 is limited to the ones listed by the ACPI ``_PSS`` objects.
756 processor is supported by it.
775 This option does not work with processors that are not supported by
781 supported by the processor.
785 hardware-managed P-states (HWP) feature is supported by the processor.
792 Server", the ACPI ``_PPC`` limits are taken into account by default
800 Do not enable `capacity-aware scheduling <CAS_>`_ which is enabled by
811 by ``CPUFreq``, and the other one is the ``pstate_sample`` trace event specific
812 to ``intel_pstate``. Both of them are triggered by ``intel_pstate`` only if
826 ``cpu_frequency`` trace event will be triggered either by the ``schedutil``
827 scaling governor (for the policies it is attached to), or by the ``CPUFreq``