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Commit aa5eee35 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

Documentation: admin-guide: PM: Add cpuidle document 



Important information is missing from user/admin cpuidle documentation
available today, so add a new user/admin document for cpuidle containing
current and comprehensive information to admin-guide and drop the old
.txt documents it is replacing.

Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: default avatarUlf Hansson <ulf.hansson@linaro.org>
parent 2e6e902d

Documentation/admin-guide/pm/cpuidle.rst

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Documentation/admin-guide/pm/working-state.rst

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@@ -5,5 +5,6 @@ Working-State Power Management 
.. toctree::

   :maxdepth: 2



   cpuidle

   cpufreq

   intel_pstate

Documentation/cpuidle/core.txt

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		Supporting multiple CPU idle levels in kernel



				cpuidle



General Information:



Various CPUs today support multiple idle levels that are differentiated

by varying exit latencies and power consumption during idle.

cpuidle is a generic in-kernel infrastructure that separates

idle policy (governor) from idle mechanism (driver) and provides a

standardized infrastructure to support independent development of

governors and drivers.



cpuidle resides under drivers/cpuidle.



Boot options:

"cpuidle_sysfs_switch"

enables current_governor interface in /sys/devices/system/cpu/cpuidle/,

which can be used to switch governors at run time. This boot option

is meant for developer testing only. In normal usage, kernel picks the

best governor based on governor ratings.

SEE ALSO: sysfs.txt in this directory.

Documentation/cpuidle/sysfs.txt

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		Supporting multiple CPU idle levels in kernel



				cpuidle sysfs



System global cpuidle related information and tunables are under

/sys/devices/system/cpu/cpuidle



The current interfaces in this directory has self-explanatory names:

* current_driver

* current_governor_ro



With cpuidle_sysfs_switch boot option (meant for developer testing)

following objects are visible instead.

* current_driver

* available_governors

* current_governor

In this case users can switch the governor at run time by writing

to current_governor.





Per logical CPU specific cpuidle information are under

/sys/devices/system/cpu/cpuX/cpuidle

for each online cpu X



--------------------------------------------------------------------------------

# ls -lR /sys/devices/system/cpu/cpu0/cpuidle/

/sys/devices/system/cpu/cpu0/cpuidle/:

total 0

drwxr-xr-x 2 root root 0 Feb  8 10:42 state0

drwxr-xr-x 2 root root 0 Feb  8 10:42 state1

drwxr-xr-x 2 root root 0 Feb  8 10:42 state2

drwxr-xr-x 2 root root 0 Feb  8 10:42 state3



/sys/devices/system/cpu/cpu0/cpuidle/state0:

total 0

-r--r--r-- 1 root root 4096 Feb  8 10:42 desc

-rw-r--r-- 1 root root 4096 Feb  8 10:42 disable

-r--r--r-- 1 root root 4096 Feb  8 10:42 latency

-r--r--r-- 1 root root 4096 Feb  8 10:42 name

-r--r--r-- 1 root root 4096 Feb  8 10:42 power

-r--r--r-- 1 root root 4096 Feb  8 10:42 residency

-r--r--r-- 1 root root 4096 Feb  8 10:42 time

-r--r--r-- 1 root root 4096 Feb  8 10:42 usage



/sys/devices/system/cpu/cpu0/cpuidle/state1:

total 0

-r--r--r-- 1 root root 4096 Feb  8 10:42 desc

-rw-r--r-- 1 root root 4096 Feb  8 10:42 disable

-r--r--r-- 1 root root 4096 Feb  8 10:42 latency

-r--r--r-- 1 root root 4096 Feb  8 10:42 name

-r--r--r-- 1 root root 4096 Feb  8 10:42 power

-r--r--r-- 1 root root 4096 Feb  8 10:42 residency

-r--r--r-- 1 root root 4096 Feb  8 10:42 time

-r--r--r-- 1 root root 4096 Feb  8 10:42 usage



/sys/devices/system/cpu/cpu0/cpuidle/state2:

total 0

-r--r--r-- 1 root root 4096 Feb  8 10:42 desc

-rw-r--r-- 1 root root 4096 Feb  8 10:42 disable

-r--r--r-- 1 root root 4096 Feb  8 10:42 latency

-r--r--r-- 1 root root 4096 Feb  8 10:42 name

-r--r--r-- 1 root root 4096 Feb  8 10:42 power

-r--r--r-- 1 root root 4096 Feb  8 10:42 residency

-r--r--r-- 1 root root 4096 Feb  8 10:42 time

-r--r--r-- 1 root root 4096 Feb  8 10:42 usage



/sys/devices/system/cpu/cpu0/cpuidle/state3:

total 0

-r--r--r-- 1 root root 4096 Feb  8 10:42 desc

-rw-r--r-- 1 root root 4096 Feb  8 10:42 disable

-r--r--r-- 1 root root 4096 Feb  8 10:42 latency

-r--r--r-- 1 root root 4096 Feb  8 10:42 name

-r--r--r-- 1 root root 4096 Feb  8 10:42 power

-r--r--r-- 1 root root 4096 Feb  8 10:42 residency

-r--r--r-- 1 root root 4096 Feb  8 10:42 time

-r--r--r-- 1 root root 4096 Feb  8 10:42 usage

--------------------------------------------------------------------------------





* desc : Small description about the idle state (string)

* disable : Option to disable this idle state (bool) -> see note below

* latency : Latency to exit out of this idle state (in microseconds)

* residency : Time after which a state becomes more effecient than any

  shallower state (in microseconds)

* name : Name of the idle state (string)

* power : Power consumed while in this idle state (in milliwatts)

* time : Total time spent in this idle state (in microseconds)

* usage : Number of times this state was entered (count)



Note:

The behavior and the effect of the disable variable depends on the

implementation of a particular governor. In the ladder governor, for

example, it is not coherent, i.e. if one is disabling a light state,

then all deeper states are disabled as well, but the disable variable

does not reflect it. Likewise, if one enables a deep state but a lighter

state still is disabled, then this has no effect.