cpuidle: Add Documentation
Documentation for cpuidle infrastructure. (resend) Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com> Reviewed-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Len Brown <len.brown@intel.com>hifive-unleashed-5.1
Venkatesh Pallipadi
Len Brown
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@ -109,6 +109,8 @@ cpu-hotplug.txt
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- document describing CPU hotplug support in the Linux kernel.
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cpu-load.txt
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- document describing how CPU load statistics are collected.
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cpuidle/
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- info on CPU_IDLE, CPU idle state management subsystem.
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cpusets.txt
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- documents the cpusets feature; assign CPUs and Mem to a set of tasks.
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cputopology.txt
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@ -0,0 +1,23 @@
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Supporting multiple CPU idle levels in kernel
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cpuidle
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General Information:
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Various CPUs today support multiple idle levels that are differentiated
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by varying exit latencies and power consumption during idle.
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cpuidle is a generic in-kernel infrastructure that separates
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idle policy (governor) from idle mechanism (driver) and provides a
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standardized infrastructure to support independent development of
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governors and drivers.
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cpuidle resides under drivers/cpuidle.
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Boot options:
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"cpuidle_sysfs_switch"
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enables current_governor interface in /sys/devices/system/cpu/cpuidle/,
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which can be used to switch governors at run time. This boot option
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is meant for developer testing only. In normal usage, kernel picks the
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best governor based on governor ratings.
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SEE ALSO: sysfs.txt in this directory.
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@ -0,0 +1,31 @@
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Supporting multiple CPU idle levels in kernel
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cpuidle drivers
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cpuidle driver hooks into the cpuidle infrastructure and handles the
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architecture/platform dependent part of CPU idle states. Driver
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provides the platform idle state detection capability and also
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has mechanisms in place to support actual entry-exit into CPU idle states.
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cpuidle driver initializes the cpuidle_device structure for each CPU device
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and registers with cpuidle using cpuidle_register_device.
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It can also support the dynamic changes (like battery <-> AC), by using
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cpuidle_pause_and_lock, cpuidle_disable_device and cpuidle_enable_device,
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cpuidle_resume_and_unlock.
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Interfaces:
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extern int cpuidle_register_driver(struct cpuidle_driver *drv);
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extern void cpuidle_unregister_driver(struct cpuidle_driver *drv);
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extern int cpuidle_register_device(struct cpuidle_device *dev);
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extern void cpuidle_unregister_device(struct cpuidle_device *dev);
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extern void cpuidle_pause_and_lock(void);
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extern void cpuidle_resume_and_unlock(void);
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extern int cpuidle_enable_device(struct cpuidle_device *dev);
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extern void cpuidle_disable_device(struct cpuidle_device *dev);
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@ -0,0 +1,29 @@
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Supporting multiple CPU idle levels in kernel
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cpuidle governors
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cpuidle governor is policy routine that decides what idle state to enter at
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any given time. cpuidle core uses different callbacks to the governor.
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* enable() to enable governor for a particular device
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* disable() to disable governor for a particular device
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* select() to select an idle state to enter
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* reflect() called after returning from the idle state, which can be used
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by the governor for some record keeping.
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More than one governor can be registered at the same time and
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users can switch between drivers using /sysfs interface (when enabled).
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More than one governor part is supported for developers to easily experiment
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with different governors. By default, most optimal governor based on your
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kernel configuration and platform will be selected by cpuidle.
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Interfaces:
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extern int cpuidle_register_governor(struct cpuidle_governor *gov);
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extern void cpuidle_unregister_governor(struct cpuidle_governor *gov);
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struct cpuidle_governor
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@ -0,0 +1,79 @@
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Supporting multiple CPU idle levels in kernel
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cpuidle sysfs
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System global cpuidle related information and tunables are under
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/sys/devices/system/cpu/cpuidle
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The current interfaces in this directory has self-explanatory names:
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* current_driver
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* current_governor_ro
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With cpuidle_sysfs_switch boot option (meant for developer testing)
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following objects are visible instead.
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* current_driver
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* available_governors
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* current_governor
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In this case users can switch the governor at run time by writing
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to current_governor.
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Per logical CPU specific cpuidle information are under
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/sys/devices/system/cpu/cpuX/cpuidle
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for each online cpu X
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--------------------------------------------------------------------------------
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# ls -lR /sys/devices/system/cpu/cpu0/cpuidle/
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/sys/devices/system/cpu/cpu0/cpuidle/:
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total 0
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drwxr-xr-x 2 root root 0 Feb 8 10:42 state0
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drwxr-xr-x 2 root root 0 Feb 8 10:42 state1
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drwxr-xr-x 2 root root 0 Feb 8 10:42 state2
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drwxr-xr-x 2 root root 0 Feb 8 10:42 state3
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/sys/devices/system/cpu/cpu0/cpuidle/state0:
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total 0
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-r--r--r-- 1 root root 4096 Feb 8 10:42 desc
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-r--r--r-- 1 root root 4096 Feb 8 10:42 latency
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-r--r--r-- 1 root root 4096 Feb 8 10:42 name
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-r--r--r-- 1 root root 4096 Feb 8 10:42 power
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-r--r--r-- 1 root root 4096 Feb 8 10:42 time
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-r--r--r-- 1 root root 4096 Feb 8 10:42 usage
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/sys/devices/system/cpu/cpu0/cpuidle/state1:
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total 0
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-r--r--r-- 1 root root 4096 Feb 8 10:42 desc
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-r--r--r-- 1 root root 4096 Feb 8 10:42 latency
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-r--r--r-- 1 root root 4096 Feb 8 10:42 name
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-r--r--r-- 1 root root 4096 Feb 8 10:42 power
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-r--r--r-- 1 root root 4096 Feb 8 10:42 time
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-r--r--r-- 1 root root 4096 Feb 8 10:42 usage
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/sys/devices/system/cpu/cpu0/cpuidle/state2:
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total 0
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-r--r--r-- 1 root root 4096 Feb 8 10:42 desc
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-r--r--r-- 1 root root 4096 Feb 8 10:42 latency
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-r--r--r-- 1 root root 4096 Feb 8 10:42 name
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-r--r--r-- 1 root root 4096 Feb 8 10:42 power
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-r--r--r-- 1 root root 4096 Feb 8 10:42 time
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-r--r--r-- 1 root root 4096 Feb 8 10:42 usage
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/sys/devices/system/cpu/cpu0/cpuidle/state3:
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total 0
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-r--r--r-- 1 root root 4096 Feb 8 10:42 desc
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-r--r--r-- 1 root root 4096 Feb 8 10:42 latency
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-r--r--r-- 1 root root 4096 Feb 8 10:42 name
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-r--r--r-- 1 root root 4096 Feb 8 10:42 power
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-r--r--r-- 1 root root 4096 Feb 8 10:42 time
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-r--r--r-- 1 root root 4096 Feb 8 10:42 usage
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--------------------------------------------------------------------------------
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* desc : Small description about the idle state (string)
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* latency : Latency to exit out of this idle state (in microseconds)
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* name : Name of the idle state (string)
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* power : Power consumed while in this idle state (in milliwatts)
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* time : Total time spent in this idle state (in microseconds)
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* usage : Number of times this state was entered (count)
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