Commit fe8e288a authored by Venkatesh Pallipadi's avatar Venkatesh Pallipadi Committed by Len Brown

cpuidle: Add Documentation

Documentation for cpuidle infrastructure. (resend)
Signed-off-by: default avatarVenkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Reviewed-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarLen Brown <len.brown@intel.com>
parent 4fcb2fcd
......@@ -109,6 +109,8 @@ cpu-hotplug.txt
- document describing CPU hotplug support in the Linux kernel.
cpu-load.txt
- document describing how CPU load statistics are collected.
cpuidle/
- info on CPU_IDLE, CPU idle state management subsystem.
cpusets.txt
- documents the cpusets feature; assign CPUs and Mem to a set of tasks.
cputopology.txt
......
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.
Supporting multiple CPU idle levels in kernel
cpuidle drivers
cpuidle driver hooks into the cpuidle infrastructure and handles the
architecture/platform dependent part of CPU idle states. Driver
provides the platform idle state detection capability and also
has mechanisms in place to support actual entry-exit into CPU idle states.
cpuidle driver initializes the cpuidle_device structure for each CPU device
and registers with cpuidle using cpuidle_register_device.
It can also support the dynamic changes (like battery <-> AC), by using
cpuidle_pause_and_lock, cpuidle_disable_device and cpuidle_enable_device,
cpuidle_resume_and_unlock.
Interfaces:
extern int cpuidle_register_driver(struct cpuidle_driver *drv);
extern void cpuidle_unregister_driver(struct cpuidle_driver *drv);
extern int cpuidle_register_device(struct cpuidle_device *dev);
extern void cpuidle_unregister_device(struct cpuidle_device *dev);
extern void cpuidle_pause_and_lock(void);
extern void cpuidle_resume_and_unlock(void);
extern int cpuidle_enable_device(struct cpuidle_device *dev);
extern void cpuidle_disable_device(struct cpuidle_device *dev);
Supporting multiple CPU idle levels in kernel
cpuidle governors
cpuidle governor is policy routine that decides what idle state to enter at
any given time. cpuidle core uses different callbacks to the governor.
* enable() to enable governor for a particular device
* disable() to disable governor for a particular device
* select() to select an idle state to enter
* reflect() called after returning from the idle state, which can be used
by the governor for some record keeping.
More than one governor can be registered at the same time and
users can switch between drivers using /sysfs interface (when enabled).
More than one governor part is supported for developers to easily experiment
with different governors. By default, most optimal governor based on your
kernel configuration and platform will be selected by cpuidle.
Interfaces:
extern int cpuidle_register_governor(struct cpuidle_governor *gov);
extern void cpuidle_unregister_governor(struct cpuidle_governor *gov);
struct cpuidle_governor
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
-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 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
-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 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
-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 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
-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 time
-r--r--r-- 1 root root 4096 Feb 8 10:42 usage
--------------------------------------------------------------------------------
* desc : Small description about the idle state (string)
* latency : Latency to exit out of this idle 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)
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