62d6ae880e
There are two cpuidle governors ladder and menu. While the ladder governor is always available, if CONFIG_CPU_IDLE is selected, the menu governor additionally requires CONFIG_NO_HZ. A particular C state can be disabled by writing to the sysfs file /sys/devices/system/cpu/cpuN/cpuidle/stateN/disable, but this mechanism is only implemented in the menu governor. Thus, in a system where CONFIG_NO_HZ is not selected, the ladder governor becomes default and always will walk through all sleep states - irrespective of whether the C state was disabled via sysfs or not. The only way to select a specific C state was to write the related latency to /dev/cpu_dma_latency and keep the file open as long as this setting was required - not very practical and not suitable for setting a single core in an SMP system. With this patch, the ladder governor only will promote to the next C state, if it has not been disabled, and it will demote, if the current C state was disabled. Note that the patch does not make the setting of the sysfs variable "disable" 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. A related section has been added to the documentation. Signed-off-by: Carsten Emde <C.Emde@osadl.org> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
92 lines
3.4 KiB
Text
92 lines
3.4 KiB
Text
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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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-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
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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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-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
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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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-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
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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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-rw-r--r-- 1 root root 4096 Feb 8 10:42 disable
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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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* disable : Option to disable this idle state (bool) -> see note below
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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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Note:
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The behavior and the effect of the disable variable depends on the
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implementation of a particular governor. In the ladder governor, for
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example, it is not coherent, i.e. if one is disabling a light state,
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then all deeper states are disabled as well, but the disable variable
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does not reflect it. Likewise, if one enables a deep state but a lighter
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state still is disabled, then this has no effect.
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