CPUFreq addon in HAL

[Holger Macht]

Hi,

CPU frequency scaling is the last remaining important power management
technology that should be controllable from the desktop IMO, but that's
not possible yet. Or there's at least no common interface/ software
everybody agrees on.

Richard already proposed something similar in the past. His idea was to
control the different frequencies a CPU supports from higher level
applications on the desktop. His proposal was rejected, though.

So I'm doing a second apprach and I've got a different way of solving the
problem. It's implemented as a HAL addon which summarizes all cpufreq
capable CPUs into six DBus methods on the
org.freedesktop.Hal.Device.SystemPowerManagement interface.

Addon-cpufreq supports kernel governors and also implements a userspace
controlling mechanism. That makes it the "all you need for CPUFreq"
application. Furthermore, to not make things unnecessarily complicated for
desktop applications, it is supposed to abstract all the different
settings you can make for the different governors. One thing which isn't
available yet, is the possibility to control the performance of
dynamically scaled CPUs. There's a method to set the performance (from 1
to 100) which can be easily used from other applications with showing a
nice progress bar or the like. That makes it unique in contrast to former
solutions.

The biggest advantage is that you get CPUFreq out of the box on every
system supporting HAL without the need to install another daemon. Another
one is that desktop applications like gnome-power-manager or kpowersave
can use one common interface after all.

It claims the following DBus interfaces on the
/org/freedesktop/Hal/devices/computer device:


Set a specific CPU frequency governor
-------------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "SetCPUFreqGovernor"
  Type     : Method call with return

  Param:
    string : The governor to be set. This can be any arbitary string. Also
	     governors which are not known can be set

  Return type:
    int    : 0 on success, 1 on error

Set the performance independently from the current governor
-----------------------------------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "SetCPUFreqPerformance"
  Type     : Method call with return

  Param:
    int    : Value between 1 and 100. The higher the value the more
	     performance you get. 50 is default and should be sufficient
	     in most cases

  Return type:
    int    : 0 on success, 1 on error or if performance settings are not
	     supported for the current governor

Set if niced processes should be consider when calculating CPU load
--------------------------------------------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "SetCPUFreqConsiderNice"
  Type     : Method call with return

  Param:
    boolean: True if niced processes should be considered, false otherwise

  Return type:
    int    : 0 on success, 1 on error or if this setting is not supported
	     with the current governor

Get the current active governor
-------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "GetCPUFreqGovernor"
  Type     : Method call with return

  Return type:
    string : The current active governor

Get the current performance setting
-----------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "GetCPUFreqPerformance"
  Type     : Method call with return

  Return type:
    int    : The current performance setting from 1 to 100

Get the current consider nice setting
-------------------------------------
  Interface: org.freedesktop.Hal.Device.SystemPowerManagement
  Member   : "GetCPUFreqConsiderNice"
  Type     : Method call with return

  Return type:
    boolean: True if niced processes are considered, false otherwise



The addon basically consists of five parts:

  1. One interface which contains all methods which are common for all
     governors (see DBus interfaces above)

  2. Some helper functions

  3. The userspace governor implementation with the CPULoad calculation
     mechanism

  4. The ondemand governor implementation

  5. DBus/HAL integration

Current addons only consist of one source file. However, I don't think
that makes sense for addon-cpufreq. If this would be a independent
project, I would have separated these parts into more different files. But
for now, I've just put the userspace part into two files (header, source)
and the remaining parts into another two files (header, source). It would
of course be possible to only have one source file and thus get rid of the
header files if this is desired.

I've appended a somewhat patch to accomplish all this. Please comment...

If you guys don't agree that this could be added to HAL as an addon, maybe
the above mentioned interfaces can be implemented by installing some
scripts like hal-system-power-cpufreq-set-governor. Then I'm trying to get
org.freedesktop.CPUFreq for a separate daemon and can call the DBus
methods inside them. All other people can then of course do whatever they
like in those scripts.


Regards,
	Holger
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