admin-guide/pm/cpufreq.rst

19 different clock frequency and voltage configurations, often referred to as
21 the higher the clock frequency and the higher the voltage, the more instructions
23 frequency and the higher the voltage, the more energy is consumed over a unit of
30 highest one (i.e. the highest-performance frequency/voltage configuration
37 different frequency/voltage configurations or (in the ACPI terminology) to be
44 to as CPU performance scaling or CPU frequency scaling (because it involves
45 adjusting the CPU clock frequency).
52 (CPU Frequency scaling) subsystem that consists of three layers of code: the
244 	Current frequency of the CPUs belonging to this policy as obtained from
247 	This is expected to be the frequency the hardware actually runs at.
248 	If that frequency cannot be determined, this attribute should not
252         An average frequency (in KHz) of all CPUs belonging to a given policy,
256         This is expected to be based on the frequency the hardware actually runs
261         Note, that failed attempt to retrieve current frequency for a given
266 	Maximum possible operating frequency the CPUs belonging to this policy
270 	Minimum possible operating frequency the CPUs belonging to this policy
299 	Current frequency of all of the CPUs belonging to this policy (in kHz).
301 	In the majority of cases, this is the frequency of the last P-state
303 	interface provided by it, which may or may not reflect the frequency
308 	more precisely reflecting the current CPU frequency through this
309 	attribute, but that still may not be the exact current CPU frequency as
329 	Maximum frequency the CPUs belonging to this policy are allowed to be
337 	Minimum frequency the CPUs belonging to this policy are allowed to be
348 	It returns the last frequency requested by the governor (in kHz) or can
349 	be written to in order to set a new frequency for the policy.
379 When attached to a policy object, this governor causes the highest frequency,
389 When attached to a policy object, this governor causes the lowest frequency,
400 to set the CPU frequency for the policy it is attached to by writing to the
411 invoke the scaling driver asynchronously when it decides that the CPU frequency
413 is capable of changing the CPU frequency from scheduler context).
417 RT or deadline scheduling classes, the governor will increase the frequency to
423 CPU frequency to apply is computed in accordance with the formula
428 ``util``, and ``f_0`` is either the maximum possible CPU frequency for the given
429 policy (if the PELT number is frequency-invariant), or the current CPU frequency
433 CPU frequency for tasks that have been waiting on I/O most recently, called
435 is passed by the scheduler to the governor callback which causes the frequency
459 This governor uses CPU load as a CPU frequency selection metric.
483 speedup threshold, in which case it will go straight for the highest frequency
506 	will set the frequency to the maximum value allowed for the policy.
507 	Otherwise, the selected frequency will be proportional to the estimated
516 	taken into account when deciding what frequency to run the CPUs at.
525 	setting the frequency to the allowed maximum) to be delayed, so the
526 	frequency stays at the maximum level for a longer time.
528 	Frequency fluctuations in some bursty workloads may be avoided this way
533 	Reduction factor to apply to the original frequency target of the
536 	for the AMD frequency sensitivity powersave bias driver
540 	If the AMD frequency sensitivity powersave bias driver is not loaded,
541 	the effective frequency to apply is given by
545 	where f is the governor's original frequency target.  The default value
548 	If the AMD frequency sensitivity powersave bias driver is loaded, the
555 	workload running on a CPU will change in response to frequency changes.
559 	the CPU frequency, whereas workloads with the sensitivity of 100%
560 	(CPU-bound) are expected to perform much better if the CPU frequency is
565 	will cause the governor to select a frequency lower than its original
572 This governor uses CPU load as a CPU frequency selection metric.
575 above, but the CPU frequency selection algorithm implemented by it is different.
577 Namely, it avoids changing the frequency significantly over short time intervals
579 battery-powered).  To achieve that, it changes the frequency in relatively
586 	Frequency step in percent of the maximum frequency the governor is
590 	This is how much the frequency is allowed to change in one go.  Setting
591 	it to 0 will cause the default frequency step (5 percent) to be used
593 	switch the frequency between the ``scaling_min_freq`` and
598 	frequency change direction.
600 	If the estimated CPU load is greater than this value, the frequency will
602 	``sampling_down_factor`` mechanism is not in effect), the frequency will
603 	go down.  Otherwise, the frequency will not be changed.
606 	Frequency decrease deferral factor, between 1 (default) and 10
609 	It effectively causes the frequency to go down ``sampling_down_factor``
613 Frequency Boost Support
619 Some processors support a mechanism to raise the operating frequency of some
620 cores in a multicore package temporarily (and above the sustainable frequency
628 term "frequency boost" is used here for brevity to refer to all of those
631 The frequency boost mechanism may be either hardware-based or software-based.
634 into a special state in which it can control the CPU frequency within certain
643 scaling driver does not support the frequency boost mechanism (or supports it,
647 If the value in this file is 1, the frequency boost mechanism is enabled.  This
652 permission to use the frequency boost mechanism (which still may never be used
655 If the value in this file is 0, the frequency boost mechanism is disabled and
663 The frequency boost mechanism is generally intended to help to achieve optimum
668 For this reason, many systems make it possible to disable the frequency boost
675      as a result of increasing its frequency and voltage, even temporarily.
685   3. To examine the impact of the frequency boost mechanism itself, it is useful
693      frequency boost mechanism before running benchmarks sensitive to that