Lines Matching +full:space +full:- +full:constraint

1 .. SPDX-License-Identifier: GPL-2.0
27 CPU idle time management is an energy-efficiency feature concerned about using
31 ------------
37 software as individual single-core processors.  In other words, a CPU is an
46 Second, if the processor is multi-core, each core in it is able to follow at
61 Finally, each core in a multi-core processor may be able to follow more than one
66 multiple individual single-core "processors", referred to as *hardware threads*
67 (or hyper-threads specifically on Intel hardware), that each can follow one
78 ---------
112 .. _idle-loop:
127 the platform or the processor architecture and organized in a one-dimensional
134 taken into account by the governor, the *target residency* and the (worst-case)
152 and exit it.  However, the CPU may be woken up by a non-timer event at any time
162 There are four ``CPUIdle`` governors available, ``menu``, `TEO <teo-gov_>`_,
165 tick can be `stopped by the idle loop <idle-cpus-and-tick_>`_.  Available
186 .. _idle-cpus-and-tick:
223 (non-tick) timer due to trigger within the tick range, stopping the tick clearly
225 reprogrammed in that case.  Second, if the governor is expecting a non-timer
247 loop altogether.  That can be done through the build-time configuration of it
255 generally regarded as more energy-efficient than the systems running kernels in
261 .. _menu-gov:
319 from the power management quality of service, or `PM QoS <cpu-pm-qos_>`_,
331 if it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_.  That
340 .. _teo-gov:
347 <menu-gov_>`_: it always tries to find the deepest idle state suitable for the
361 Like in the ``menu`` governor `case <menu-gov_>`_, the first step is to obtain
369 state will "match" the observed (post-wakeup) idle duration if it "matches" the
384 "match" the observed (post-wakeup) idle duration if it does not "match" the
386 when the idle state corresponding to it "matches" the observed (post-wakeup)
400 [If there is a wakeup latency constraint coming from the `PM QoS framework
401 <cpu-pm-qos_>`_ which is hit before reaching the deepest idle state with the
403 latency within the constraint is preselected without consulting the ``hits``,
416 it has not decided to `stop the scheduler tick <idle-cpus-and-tick_>`_.  That
420 `case <menu-gov_>`_, the sleep length used in the previous computations may not
426 .. _idle-states-representation:
432 supported by the processor have to be represented as a one-dimensional array of
438 of it <idle-loop_>`_, must reflect the properties of the idle state at the
537 description may be longer and it may contain white space or special characters.
585 .. _cpu-pm-qos:
591 allows kernel code and user space processes to set constraints on various
592 energy-efficiency features of the kernel to prevent performance from dropping
599 space can modify the former by opening the :file:`cpu_dma_latency` special
601 signed 32-bit integer) to it.  In turn, the resume latency constraint for a CPU
602 can be modified from user space by writing a string (representing a signed
603 32-bit integer) to the :file:`power/pm_qos_resume_latency_us` file under
607 number will be interpreted as a requested PM QoS constraint in microseconds.
609 The requested value is not automatically applied as a new constraint, however,
611 constraint previously requested by someone else.  For this reason, the PM QoS
615 constraint.
644 this single PM QoS request to be updated regardless of which user space
646 user space, so access to the file associated with it needs to be arbitrated
649 ``sysfs`` interface to control the resume latency constraint for it.]  It is
651 determine the effective value to be set as the resume latency constraint for the
656 (effective) CPU latency limit and the effective resume latency constraint for
666 `disabled for individual CPUs <idle-states-representation_>`_, there are kernel
677 however, so it is rather crude and not very energy-efficient.  For this reason,
706 P-states (see |cpufreq|) that require any number of CPUs in a package to be
707 idle, so it very well may hurt single-thread computations performance as well as
708 energy-efficiency.  Thus using it for performance reasons may not be a good idea
719 In addition to the architecture-level kernel command line options affecting CPU
725 `Representation of Idle States <idle-states-representation_>`_), causes the