【cpuidle】计算每个cpu进入idle的时间

参考内核文档

		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.

其中time显示了每个idle阶段的时间长短。

前后两次idle/state*/time的时间即是进入idle的时间。