Lines Matching refs:scaling
45 to as CPU performance scaling or CPU frequency scaling (because it involves
52 The Linux kernel supports CPU performance scaling by means of the ``CPUFreq``
53 (CPU Frequency scaling) subsystem that consists of three layers of code: the
54 core, scaling governors and scaling drivers.
57 interfaces for all platforms that support CPU performance scaling. It defines
61 As a rule, each governor implements one, possibly parametrized, scaling
64 Scaling drivers talk to the hardware. They provide scaling governors with
67 by scaling governors.
69 In principle, all available scaling governors can be used with every scaling
71 performance scaling algorithms for P-state selection can be represented in a
73 to use the same performance scaling algorithm implemented in exactly the same
74 way regardless of which scaling driver is used. Consequently, the same set of
75 scaling governors should be suitable for every supported platform.
77 However, that observation may not hold for performance scaling algorithms
81 platform-independent way. For this reason, ``CPUFreq`` allows scaling drivers
82 to bypass the governor layer and implement their own performance scaling
83 algorithms. That is done by the |intel_pstate| scaling driver.
111 First of all, a scaling driver has to be registered for ``CPUFreq`` to work.
112 It is only possible to register one scaling driver at a time, so the scaling
115 The scaling driver may be registered before or after CPU registration. If
118 scaling driver. In turn, if any CPUs are registered after the registration of
119 the scaling driver, the ``CPUFreq`` core will be invoked to take note of them
136 Next, the scaling driver's ``->init()`` callback is invoked with the policy
138 to initialize the performance scaling hardware interface for the given CPU (or,
149 scaling governor to it (to begin with, that is the default scaling governor
164 invoke the scaling driver to make changes to the hardware in accordance with
165 the P-state selection. The scaling driver may be invoked directly from
167 on the configuration and capabilities of the scaling driver and the governor.
172 to use the scaling governor previously used with the policy that became
178 necessary to restart the scaling governor so that it can take the new online CPU
182 As mentioned before, the |intel_pstate| scaling driver bypasses the scaling
184 Consequently, if |intel_pstate| is used, scaling governors are not attached to
187 callbacks are invoked by the CPU scheduler in the same way as for scaling
193 associated with them are torn down when the scaling driver is unregistered
216 and their behavior generally does not depend on what scaling driver is in use
217 and what scaling governor is attached to the given policy. Some scaling drivers
226 performance scaling interface represented by the ``policyX`` policy
241 This attribute is not present if the scaling driver in use does not
264 If unknown or if known to be so high that the scaling driver does not
272 List of ``CPUFreq`` scaling governors present in the kernel that can
273 be attached to this policy or (if the |intel_pstate| scaling driver is
274 in use) list of scaling algorithms provided by the driver that can be
285 requested by the scaling driver from the hardware using the scaling
296 The scaling driver currently in use.
299 The scaling governor currently attached to this policy or (if the
300 |intel_pstate| scaling driver is in use) the scaling algorithm
303 This attribute is read-write and writing to it will cause a new scaling
304 governor to be attached to this policy or a new scaling algorithm
305 provided by the scaling driver to be applied to it (in the
327 This attribute is functional only if the `userspace`_ scaling governor
337 ``CPUFreq`` provides generic scaling governors that can be used with all
338 scaling drivers. As stated before, each of them implements a single, possibly
339 parametrized, performance scaling algorithm.
342 can be handled by different scaling governors at the same time (although that
345 The scaling governor for a given policy object can be changed at any time with
348 Some governors expose ``sysfs`` attributes to control or fine-tune the scaling
351 scaling driver in use. If the driver requires governor tunables to be
393 invoke the scaling driver asynchronously when it decides that the CPU frequency
425 runs of governor computations (default: 1000 times the scaling driver's
617 limits). If it is software-based (e.g. on ARM), the scaling driver decides
625 scaling driver does not support the frequency boost mechanism (or supports it,
681 The AMD powernow-k8 scaling driver supports a ``sysfs`` knob very similar to