Lines Matching +full:higher +full:- +full:than +full:- +full:threshold
1 .. SPDX-License-Identifier: GPL-2.0
22 Documentation/admin-guide/pm/cpufreq.rst if you have not done that yet.]
24 For the processors supported by ``intel_pstate``, the P-state concept is broader
25 than just an operating frequency or an operating performance point (see the
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
43 time the corresponding CPU is taken offline and need to be re-initialized when
47 only way to pass early-configuration-time parameters to it is via the kernel
66 -----------
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
121 Energy-Performance Preference (EPP) knob (if supported) or its
122 Energy-Performance Bias (EPB) knob (otherwise), which means that the processor's
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).
138 Energy-Performance Preference (EPP) knob (if supported) or its
139 Energy-Performance Bias (EPB) knob (otherwise) to whatever value it was
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
186 given CPU when it is invoked by the CPU scheduler, but not more often than
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
196 ------------
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
222 the so-called "turbo" frequency ranges). In other words, in the passive mode
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
236 ``intel_pstate`` can be divided into two sub-ranges that correspond to
238 will be referred to as the "turbo threshold" in what follows.
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
248 (that is, above the turbo threshold), the processor is permitted to take over
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
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
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
292 used relative to ACPI-based CPU performance scaling (see `below <acpi-cpufreq_>`_
295 Moreover, since ``intel_pstate`` always knows what the real turbo threshold 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.
322 itself (using model-specific registers), there are cases in which hardware
336 cores differing by the maximum turbo P-state, performance vs power characteristics,
344 --------------------------
348 one core, ``intel_pstate`` assigns performance-based priorities to CPUs. Namely,
362 more energy-efficient ways.
366 Capacity-Aware Scheduling Support
367 ---------------------------------
369 The capacity-aware scheduling (CAS) support in the CPU scheduler is enabled by
381 balanced because the more performant CPUs are generally less energy-efficient
382 than the less performant ones.
385 the system and it needs to be able to compute scale-invariant utilization of
391 units are the same for all CPUs. Second, the frequency-invariance computations,
398 Energy-Aware Scheduling Support
399 -------------------------------
404 Energy-Aware Scheduling (EAS) support to be enabled in the CPU scheduler if
413 a less performant (small) CPU appears to be always cheaper than running that
416 current utilization is higher generally appears to be a more expensive
420 Since EAS works on top of CAS, high-utilization tasks are always migrated to
421 CPUs with enough capacity to accommodate them, but thanks to EAS, low-utilization
436 -----------------
446 Maximum P-state the driver is allowed to set in percent of the
448 P-state <turbo_>`_).
455 Minimum P-state the driver is allowed to set in percent of the
457 P-state <turbo_>`_).
464 Number of P-states supported by the processor (between 0 and 255
465 inclusive) including both turbo and non-turbo P-states (see
466 `Turbo P-states Support`_).
474 This attribute is read-only.
478 range of supported P-states, in percent.
483 This attribute is read-only.
488 If set (equal to 1), the driver is not allowed to set any turbo P-states
489 (see `Turbo P-states Support`_). If unset (equal to 0, which is the
490 default), turbo P-states can be set by the driver.
497 but it affects the maximum possible value of per-policy P-state limits
503 the processor. If set (equal to 1), it causes the minimum P-state limit
508 This setting has no effect on logical CPUs whose minimum P-state limit
509 is directly set to the highest non-turbo P-state or above it.
532 that string - or to be unregistered in the "off" case. [Actually,
536 as well as the per-policy ones) are then reset to their default
541 Lake or Coffee Lake desktop CPU model. By default, energy-efficiency
543 Enabling energy-efficiency optimizations may limit maximum operating
547 attribute to "1" enables the energy-efficiency optimizations and setting
551 -----------------------------------
554 Documentation/admin-guide/pm/cpufreq.rst is special with ``intel_pstate``
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
566 not allowed to use turbo P-states, so the maximum value of ``scaling_max_freq``
567 and ``scaling_min_freq`` is limited to the maximum non-turbo P-state frequency.
575 and ``scaling_min_freq`` corresponds to the maximum supported turbo P-state,
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
608 Coordination of P-State Limits
609 ------------------------------
611 ``intel_pstate`` allows P-state limits to be set in two ways: with the help of
618 requested to run faster than the global maximum and none of them can be
619 requested to run slower than the global minimum).
621 2. Each individual CPU is affected by its own per-policy limits (that is, it
622 cannot be requested to run faster than its own per-policy maximum and it
623 cannot be requested to run slower than its own per-policy minimum). The
625 P-states, hyper-threading is enabled and on current performance requests
626 from other CPUs. When platform doesn't support per core P-states, the
627 effective performance can be more than the policy limits set on a CPU, if
628 other CPUs are requesting higher performance at that moment. Even with per
629 core P-states support, when hyper-threading is enabled, if the sibling CPU
630 is requesting higher performance, the other siblings will get higher
631 performance than their policy limits.
633 3. The global and per-policy limits can be set independently.
637 limits change in order to request its internal P-state selection logic to always
638 set P-states within these limits. Otherwise, the limits are taken into account
640 every time before setting a new P-state for a CPU.
648 ---------------------------
650 If the hardware-managed P-states (HWP) is enabled in the processor, additional
652 processor's internal P-state selection logic by focusing it on performance or on
653 energy-efficiency, or somewhere between the two extremes, are present in every
667 self-explanatory, except that ``default`` represents whatever hint
672 Energy-Performance Preference (EPP) knob (if supported) or its
673 Energy-Performance Bias (EPB) knob. It is also possible to write a positive
680 load-balancing algorithm and if different energy vs performance hints are
685 .. _acpi-cpufreq:
687 ``intel_pstate`` vs ``acpi-cpufreq``
697 ``acpi-cpufreq`` scaling driver. On systems supported by ``intel_pstate``
698 the ``acpi-cpufreq`` driver uses the same hardware CPU performance scaling
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
703 the corresponding CPU which basically is a subset of the P-states range that can
707 than the frequency of the highest non-turbo P-state listed by it, but the
708 corresponding P-state representation (following the hardware specification)
709 returned for it matches the maximum supported turbo P-state (or is 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
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,
724 (possibly multiplied by a constant), then it will tend to choose P-states below
725 the turbo threshold if ``acpi-cpufreq`` is used as the scaling driver, because
729 benefit from running at turbo frequencies will be given non-turbo P-states
734 turbo threshold. Namely, if that is not coordinated with the lists of P-states
735 returned by ``_PSS`` properly, there may be more than one item corresponding to
736 a turbo P-state in those lists and there may be a problem with avoiding the
738 P-states overall, ``acpi-cpufreq`` simply avoids using the topmost state listed
739 by ``_PSS``, but that is not sufficient when there are other turbo P-states in
742 Apart from the above, ``acpi-cpufreq`` works like ``intel_pstate`` in the
743 `passive mode <Passive Mode_>`_, except that the number of P-states it can set
750 Several kernel command line options can be used to pass early-configuration-time
768 ``acpi-cpufreq`` even if the latter is preferred on the given system.
771 power capping) that rely on the availability of ACPI P-states
776 ``intel_pstate`` and on platforms where the ``pcc-cpufreq`` scaling
777 driver is used instead of ``acpi-cpufreq``.
780 Do not enable the hardware-managed P-states (HWP) feature even if it is
785 hardware-managed P-states (HWP) feature is supported by the processor.
796 Use per-logical-CPU P-State limits (see `Coordination of P-state
800 Do not enable `capacity-aware scheduling <CAS_>`_ which is enabled by
807 ------------
822 …gnome-terminal--4510 [001] ..s. 1177.680733: pstate_sample: core_busy=107 scaled=94 from=26 to=2…
823 cat-5235 [002] ..s. 1177.681723: cpu_frequency: state=2900000 cpu_id=2
831 ----------
833 The ``ftrace`` interface can be used for low-level diagnostics of
835 P-state is called, the ``ftrace`` filter can be set to
839 # cat available_filter_functions | grep -i pstate
845 # cat trace | head -15
848 # entries-in-buffer/entries-written: 80/80 #P:4
850 # _-----=> irqs-off
851 # / _----=> need-resched
852 # | / _---=> hardirq/softirq
853 # || / _--=> preempt-depth
855 # TASK-PID CPU# |||| TIMESTAMP FUNCTION
857 Xorg-3129 [000] ..s. 2537.644844: intel_pstate_set_pstate <-intel_pstate_timer_func
858 gnome-terminal--4510 [002] ..s. 2537.649844: intel_pstate_set_pstate <-intel_pstate_timer_func
859 gnome-shell-3409 [001] ..s. 2537.650850: intel_pstate_set_pstate <-intel_pstate_timer_func
860 <idle>-0 [000] ..s. 2537.654843: intel_pstate_set_pstate <-intel_pstate_timer_func
869 .. [2] *Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 3: System Programming …
870 …com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-system…