Lines Matching +full:boost +full:- +full:bypass
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
81 to bypass the governor layer and implement their own performance scaling
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.
235 BIOS/HW-based mechanisms.
261 P-state to another, in nanoseconds.
264 work with the `ondemand`_ governor, -1 (:c:macro:`CPUFREQ_ETERNAL`)
283 In the majority of cases, this is the frequency of the last P-state
302 This attribute is read-write and writing to it will cause a new scaling
313 This attribute is read-write and writing a string representing an
321 This attribute is read-write and writing a string representing a
322 non-negative integer to it will cause a new limit to be set (it must not
347 Some governors expose ``sysfs`` attributes to control or fine-tune the scaling
349 tunables, can be either global (system-wide) or per-policy, depending on the
351 per-policy, they are located in a subdirectory of each policy directory.
358 ---------------
368 -------------
378 -------------
385 -------------
401 Per-Entity Load Tracking (PELT) metric for the root control group of the
402 given CPU as the CPU utilization estimate (see the *Per-entity load tracking*
410 policy (if the PELT number is frequency-invariant), or the current CPU frequency
415 "IO-wait boosting". That happens when the :c:macro:`SCHED_CPUFREQ_IOWAIT` flag
438 ------------
444 time in which the given CPU was not idle. The ratio of the non-idle (active)
452 invoked asynchronously (via a workqueue) and CPU P-states are updated from
455 relatively often and the CPU P-state updates triggered by it can be relatively
480 If this tunable is per-policy, the following shell command sets the time
524 f * (1 - ``powersave_bias`` / 1000)
538 The performance of a workload with the sensitivity of 0 (memory-bound or
539 IO-bound) is not expected to increase at all as a result of increasing
541 (CPU-bound) are expected to perform much better if the CPU frequency is
547 target, so as to avoid over-provisioning workloads that will not benefit
551 ----------------
560 battery-powered). To achieve that, it changes the frequency in relatively
561 small steps, one step at a time, up or down - depending on whether or not a
594 Frequency Boost Support
598 ----------
606 For Intel processors it is referred to as "Turbo Boost", AMD calls it
607 "Turbo-Core" or (in technical documentation) "Core Performance Boost" and so on.
609 term "frequency boost" is used here for brevity to refer to all of those
612 The frequency boost mechanism may be either hardware-based or software-based.
613 If it is hardware-based (e.g. on x86), the decision to trigger the boosting is
616 limits). If it is software-based (e.g. on ARM), the scaling driver decides
619 The ``boost`` File in ``sysfs``
620 -------------------------------
623 the "boost" setting for the whole system. It is not present if the underlying
624 scaling driver does not support the frequency boost mechanism (or supports it,
625 but provides a driver-specific interface for controlling it, like
628 If the value in this file is 1, the frequency boost mechanism is enabled. This
630 trigger boosting (in the hardware-based case), or the software is allowed to
631 trigger boosting (in the software-based case). It does not mean that boosting
633 permission to use the frequency boost mechanism (which still may never be used
636 If the value in this file is 0, the frequency boost mechanism is disabled and
641 Rationale for Boost Control Knob
642 --------------------------------
644 The frequency boost mechanism is generally intended to help to achieve optimum
649 For this reason, many systems make it possible to disable the frequency boost
658 limited capacity, such as batteries, so the ability to disable the boost
666 3. To examine the impact of the frequency boost mechanism itself, it is useful
672 single-thread performance may vary because of it which may lead to
674 frequency boost mechanism before running benchmarks sensitive to that
678 -----------------------
680 The AMD powernow-k8 scaling driver supports a ``sysfs`` knob very similar to
681 the global ``boost`` one. It is used for disabling/enabling the "Core
682 Performance Boost" feature of some AMD processors.
687 implementation, however, works on the system-wide basis and setting that knob
694 ``boost`` knob is present regardless. Thus it is always possible use the
695 ``boost`` knob instead of the ``cpb`` one which is highly recommended, as that
707 .. [1] Jonathan Corbet, *Per-entity load tracking*,