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.
275 P-state to another, in nanoseconds.
297 In the majority of cases, this is the frequency of the last P-state
317 This attribute is read-write and writing to it will cause a new scaling
328 This attribute is read-write and writing a string representing an
336 This attribute is read-write and writing a string representing a
337 non-negative integer to it will cause a new limit to be set (it must not
362 Some governors expose ``sysfs`` attributes to control or fine-tune the scaling
364 tunables, can be either global (system-wide) or per-policy, depending on the
366 per-policy, they are located in a subdirectory of each policy directory.
373 ---------------
383 -------------
393 -------------
402 -------------
418 Per-Entity Load Tracking (PELT) metric for the root control group of the
419 given CPU as the CPU utilization estimate (see the *Per-entity load tracking*
427 policy (if the PELT number is frequency-invariant), or the current CPU frequency
432 "IO-wait boosting". That happens when the :c:macro:`SCHED_CPUFREQ_IOWAIT` flag
455 ------------
461 time in which the given CPU was not idle. The ratio of the non-idle (active)
469 invoked asynchronously (via a workqueue) and CPU P-states are updated from
472 relatively often and the CPU P-state updates triggered by it can be relatively
496 If this tunable is per-policy, the following shell command sets the time
541 f * (1 - ``powersave_bias`` / 1000)
555 The performance of a workload with the sensitivity of 0 (memory-bound or
556 IO-bound) is not expected to increase at all as a result of increasing
558 (CPU-bound) are expected to perform much better if the CPU frequency is
564 target, so as to avoid over-provisioning workloads that will not benefit
568 ----------------
577 battery-powered). To achieve that, it changes the frequency in relatively
578 small steps, one step at a time, up or down - depending on whether or not a
611 Frequency Boost Support
615 ----------
623 For Intel processors it is referred to as "Turbo Boost", AMD calls it
624 "Turbo-Core" or (in technical documentation) "Core Performance Boost" and so on.
626 term "frequency boost" is used here for brevity to refer to all of those
629 The frequency boost mechanism may be either hardware-based or software-based.
630 If it is hardware-based (e.g. on x86), the decision to trigger the boosting is
633 limits). If it is software-based (e.g. on ARM), the scaling driver decides
636 The ``boost`` File in ``sysfs``
637 -------------------------------
640 the "boost" setting for the whole system. It is not present if the underlying
641 scaling driver does not support the frequency boost mechanism (or supports it,
642 but provides a driver-specific interface for controlling it, like
645 If the value in this file is 1, the frequency boost mechanism is enabled. This
647 trigger boosting (in the hardware-based case), or the software is allowed to
648 trigger boosting (in the software-based case). It does not mean that boosting
650 permission to use the frequency boost mechanism (which still may never be used
653 If the value in this file is 0, the frequency boost mechanism is disabled and
658 Rationale for Boost Control Knob
659 --------------------------------
661 The frequency boost mechanism is generally intended to help to achieve optimum
666 For this reason, many systems make it possible to disable the frequency boost
675 limited capacity, such as batteries, so the ability to disable the boost
683 3. To examine the impact of the frequency boost mechanism itself, it is useful
689 single-thread performance may vary because of it which may lead to
691 frequency boost mechanism before running benchmarks sensitive to that
695 -----------------------
697 The AMD powernow-k8 scaling driver supports a ``sysfs`` knob very similar to
698 the global ``boost`` one. It is used for disabling/enabling the "Core
699 Performance Boost" feature of some AMD processors.
704 implementation, however, works on the system-wide basis and setting that knob
711 ``boost`` knob is present regardless. Thus it is always possible use the
712 ``boost`` knob instead of the ``cpb`` one which is highly recommended, as that
724 .. [1] Jonathan Corbet, *Per-entity load tracking*,