Lines Matching +full:current +full:- +full:boost +full:- +full:limit
1 .. SPDX-License-Identifier: GPL-2.0
20 Operating Performance Points or P-states (in ACPI terminology). As a rule,
24 time (or the more power is drawn) by the CPU in the given P-state. Therefore
29 as possible and then there is no reason to use any P-states different from the
30 highest one (i.e. the highest-performance frequency/voltage configuration
38 put into different P-states.
41 capacity, so as to decide which P-states to put the CPUs into. Of course, since
64 information on the available P-states (or P-state ranges in some cases) and
65 access platform-specific hardware interfaces to change CPU P-states as requested
70 performance scaling algorithms for P-state selection can be represented in a
71 platform-independent form in the majority of cases, so it should be possible
80 platform-independent way. For this reason, ``CPUFreq`` allows scaling drivers
88 In some cases the hardware interface for P-state control is shared by multiple
90 control the P-state of multiple CPUs at the same time and writing to it affects
93 Sets of CPUs sharing hardware P-state control interfaces are represented by
100 CPUs share the same hardware P-state control interface, all of the pointers
123 logical CPU may be a physical single-core processor, or a single core in a
135 Next, the scaling driver's ``->init()`` callback is invoked with the policy
142 the set of supported P-states is not a continuous range), and the mask of CPUs
151 the governor's ``->init()`` callback which is expected to initialize all of the
154 invoking its ``->start()`` callback.
156 That callback is expected to register per-CPU utilization update callbacks for
162 to determine the P-state to use for the given policy going forward and to
164 the P-state selection. The scaling driver may be invoked directly from
172 "inactive" (and is re-initialized now) instead of the default governor.
176 need to re-initialize the policy object at all. In that case, it only is
178 into account. That is achieved by invoking the governor's ``->stop`` and
179 ``->start()`` callbacks, in this order, for the entire policy.
182 governor layer of ``CPUFreq`` and provides its own P-state selection algorithms.
184 new policy objects. Instead, the driver's ``->setpolicy()`` callback is invoked
185 to register per-CPU utilization update callbacks for each policy. These
187 governors, but in the |intel_pstate| case they both determine the P-state to
210 in :file:`/sys/devices/system/cpu/cpufreq` each contain policy-specific
217 also add driver-specific attributes to the policy directories in ``sysfs`` to
218 control policy-specific aspects of driver behavior.
229 If the platform firmware (BIOS) tells the OS to apply an upper limit to
230 CPU frequencies, that limit will be reported through this attribute (if
233 The existence of the limit may be a result of some (often unintentional)
235 BIOS/HW-based mechanisms.
244 Current frequency of the CPUs belonging to this policy as obtained from
261 P-state to another, in nanoseconds.
264 work with the `ondemand`_ governor, -1 (:c:macro:`CPUFREQ_ETERNAL`)
285 Current frequency of all of the CPUs belonging to this policy (in kHz).
287 In the majority of cases, this is the frequency of the last P-state
294 more precisely reflecting the current CPU frequency through this
295 attribute, but that still may not be the exact current CPU frequency as
306 This attribute is read-write and writing to it will cause a new scaling
317 This attribute is read-write and writing a string representing an
318 integer to it will cause a new limit to be set (it must not be lower
325 This attribute is read-write and writing a string representing a
326 non-negative integer to it will cause a new limit to be set (it must not
351 Some governors expose ``sysfs`` attributes to control or fine-tune the scaling
353 tunables, can be either global (system-wide) or per-policy, depending on the
355 per-policy, they are located in a subdirectory of each policy directory.
362 ---------------
365 within the ``scaling_max_freq`` policy limit, to be requested for that policy.
372 -------------
375 within the ``scaling_min_freq`` policy limit, to be requested for that policy.
382 -------------
389 -------------
403 the allowed maximum (that is, the ``scaling_max_freq`` policy limit). In turn,
405 Per-Entity Load Tracking (PELT) metric for the root control group of the
406 given CPU as the CPU utilization estimate (see the *Per-entity load tracking*
414 policy (if the PELT number is frequency-invariant), or the current CPU frequency
419 "IO-wait boosting". That happens when the :c:macro:`SCHED_CPUFREQ_IOWAIT` flag
442 ------------
446 In order to estimate the current CPU load, it measures the time elapsed between
448 time in which the given CPU was not idle. The ratio of the non-idle (active)
456 invoked asynchronously (via a workqueue) and CPU P-states are updated from
459 relatively often and the CPU P-state updates triggered by it can be relatively
469 it is allowed to use (the ``scaling_max_freq`` policy limit).
483 If this tunable is per-policy, the following shell command sets the time
528 f * (1 - ``powersave_bias`` / 1000)
542 The performance of a workload with the sensitivity of 0 (memory-bound or
543 IO-bound) is not expected to increase at all as a result of increasing
545 (CPU-bound) are expected to perform much better if the CPU frequency is
551 target, so as to avoid over-provisioning workloads that will not benefit
555 ----------------
564 battery-powered). To achieve that, it changes the frequency in relatively
565 small steps, one step at a time, up or down - depending on whether or not a
572 allowed to set (the ``scaling_max_freq`` policy limit), between 0 and
598 Frequency Boost Support
602 ----------
610 For Intel processors it is referred to as "Turbo Boost", AMD calls it
611 "Turbo-Core" or (in technical documentation) "Core Performance Boost" and so on.
613 term "frequency boost" is used here for brevity to refer to all of those
616 The frequency boost mechanism may be either hardware-based or software-based.
617 If it is hardware-based (e.g. on x86), the decision to trigger the boosting is
620 limits). If it is software-based (e.g. on ARM), the scaling driver decides
623 The ``boost`` File in ``sysfs``
624 -------------------------------
627 the "boost" setting for the whole system. It is not present if the underlying
628 scaling driver does not support the frequency boost mechanism (or supports it,
629 but provides a driver-specific interface for controlling it, like
632 If the value in this file is 1, the frequency boost mechanism is enabled. This
634 trigger boosting (in the hardware-based case), or the software is allowed to
635 trigger boosting (in the software-based case). It does not mean that boosting
637 permission to use the frequency boost mechanism (which still may never be used
640 If the value in this file is 0, the frequency boost mechanism is disabled and
645 Rationale for Boost Control Knob
646 --------------------------------
648 The frequency boost mechanism is generally intended to help to achieve optimum
653 For this reason, many systems make it possible to disable the frequency boost
662 limited capacity, such as batteries, so the ability to disable the boost
670 3. To examine the impact of the frequency boost mechanism itself, it is useful
676 single-thread performance may vary because of it which may lead to
678 frequency boost mechanism before running benchmarks sensitive to that
682 -----------------------
684 The AMD powernow-k8 scaling driver supports a ``sysfs`` knob very similar to
685 the global ``boost`` one. It is used for disabling/enabling the "Core
686 Performance Boost" feature of some AMD processors.
691 implementation, however, works on the system-wide basis and setting that knob
698 ``boost`` knob is present regardless. Thus it is always possible use the
699 ``boost`` knob instead of the ``cpb`` one which is highly recommended, as that
711 .. [1] Jonathan Corbet, *Per-entity load tracking*,