Merge pull request #1535 from tycho/implement-cpuidle-plugin

cpuidle.chart.py: add plugin for monitoring cpuidle states

diff --combined python.d/README.md
index 9e18f3eb8c9231d179074cf9e2bdf1abc6706fd8,3a97da5cbb90395acbb255af270f1ab34bea1faa..d0ad5120f2be4c59b6298cef8500edab5c1081fe
--- 1/python.d/README.md
--- 2/python.d/README.md
+++ b/python.d/README.md
@@@ -186,21 -186,13 +186,21 @@@ If no configuration is given, module wi
  
  ---
  
 -
  # cpufreq
  
 -Module shows current cpu frequency by looking at appropriate files in /sys/devices
 +This module shows the current CPU frequency as set by the cpufreq kernel
 +module.
  
  **Requirement:**
 -Processor which presents data scaling frequency data
 +You need to have `CONFIG_CPU_FREQ` and (optionally) `CONFIG_CPU_FREQ_STAT`
 +enabled in your kernel.
 +
 +This module tries to read from one of two possible locations. On
 +initialization, it tries to read the `time_in_state` files provided by
 +cpufreq\_stats. If this file does not exist, or doesn't contain valid data, it
 +falls back to using the more inaccurate `scaling_cur_freq` file (which only
 +represents the **current** CPU frequency, and doesn't account for any state
 +changes which happen between updates).
  
  It produces one chart with multiple lines (one line per core).
  
@@@ -212,11 -204,23 +212,23 @@@ Sample
  sys_dir: "/sys/devices"
  ```
  
 -If no configuration is given, module will search for `scaling_cur_freq` files in `/sys/devices` directory.
 +If no configuration is given, module will search for cpufreq files in `/sys/devices` directory.
  Directory is also prefixed with `NETDATA_HOST_PREFIX` if specified.
  
  ---
  
+ # cpuidle
+ 
+ This module monitors the usage of CPU idle states.
+ 
+ **Requirement:**
+ Your kernel needs to have `CONFIG_CPU_IDLE` enabled.
+ 
+ It produces one stacked chart per CPU, showing the percentage of time spent in
+ each state.
+ 
+ ---
+ 
  # dovecot
  
  This module provides statistics information from dovecot server.