Lines Matching refs:scaling
41 to as CPU performance scaling or CPU frequency scaling (because it involves
48 The Linux kernel supports CPU performance scaling by means of the ``CPUFreq``
49 (CPU Frequency scaling) subsystem that consists of three layers of code: the
50 core, scaling governors and scaling drivers.
53 interfaces for all platforms that support CPU performance scaling. It defines
57 As a rule, each governor implements one, possibly parametrized, scaling
60 Scaling drivers talk to the hardware. They provide scaling governors with
63 by scaling governors.
65 In principle, all available scaling governors can be used with every scaling
67 performance scaling algorithms for P-state selection can be represented in a
69 to use the same performance scaling algorithm implemented in exactly the same
70 way regardless of which scaling driver is used. Consequently, the same set of
71 scaling governors should be suitable for every supported platform.
73 However, that observation may not hold for performance scaling algorithms
77 platform-independent way. For this reason, ``CPUFreq`` allows scaling drivers
78 to bypass the governor layer and implement their own performance scaling
79 algorithms. That is done by the |intel_pstate| scaling driver.
107 First of all, a scaling driver has to be registered for ``CPUFreq`` to work.
108 It is only possible to register one scaling driver at a time, so the scaling
111 The scaling driver may be registered before or after CPU registration. If
114 scaling driver. In turn, if any CPUs are registered after the registration of
115 the scaling driver, the ``CPUFreq`` core will be invoked to take note of them
132 Next, the scaling driver's ``->init()`` callback is invoked with the policy
134 to initialize the performance scaling hardware interface for the given CPU (or,
145 scaling governor to it (to begin with, that is the default scaling governor
160 invoke the scaling driver to make changes to the hardware in accordance with
161 the P-state selection. The scaling driver may be invoked directly from
163 on the configuration and capabilities of the scaling driver and the governor.
168 to use the scaling governor previously used with the policy that became
174 necessary to restart the scaling governor so that it can take the new online CPU
178 As mentioned before, the |intel_pstate| scaling driver bypasses the scaling
180 Consequently, if |intel_pstate| is used, scaling governors are not attached to
183 callbacks are invoked by the CPU scheduler in the same way as for scaling
189 associated with them are torn down when the scaling driver is unregistered
212 and their behavior generally does not depend on what scaling driver is in use
213 and what scaling governor is attached to the given policy. Some scaling drivers
222 performance scaling interface represented by the ``policyX`` policy
237 This attribute is not present if the scaling driver in use does not
260 If unknown or if known to be so high that the scaling driver does not
268 List of ``CPUFreq`` scaling governors present in the kernel that can
269 be attached to this policy or (if the |intel_pstate| scaling driver is
270 in use) list of scaling algorithms provided by the driver that can be
281 requested by the scaling driver from the hardware using the scaling
292 The scaling driver currently in use.
295 The scaling governor currently attached to this policy or (if the
296 |intel_pstate| scaling driver is in use) the scaling algorithm
299 This attribute is read-write and writing to it will cause a new scaling
300 governor to be attached to this policy or a new scaling algorithm
301 provided by the scaling driver to be applied to it (in the
323 This attribute is functional only if the `userspace`_ scaling governor
333 ``CPUFreq`` provides generic scaling governors that can be used with all
334 scaling drivers. As stated before, each of them implements a single, possibly
335 parametrized, performance scaling algorithm.
338 can be handled by different scaling governors at the same time (although that
341 The scaling governor for a given policy object can be changed at any time with
344 Some governors expose ``sysfs`` attributes to control or fine-tune the scaling
347 scaling driver in use. If the driver requires governor tunables to be
389 invoke the scaling driver asynchronously when it decides that the CPU frequency
421 runs of governor computations (default: 1000 times the scaling driver's
613 limits). If it is software-based (e.g. on ARM), the scaling driver decides
621 scaling driver does not support the frequency boost mechanism (or supports it,
677 The AMD powernow-k8 scaling driver supports a ``sysfs`` knob very similar to