CPUFreq addon in HAL

[Holger Macht]

On Wed 05. Jul - 17:31:09, Kevin Ottens wrote:
> Le mercredi 5 juillet 2006 16:49, Holger Macht a écrit :
> > [...]
> > 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.
> 
> I personally like the idea. That's one of the missing pieces on HAL 
> powermanagement features and I'd really like to see the feature available.
> 
> I'd like to make a few comments on the proposed interface.
> 
> > 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
> 
> Shouldn't the return type be a boolean?
> That looks odd to use an int here.

Yes, of course it can be a boolean. I chose a int because most other
methods on the org.freedesktop.Hal.Device.SystemPowerManagement interface
are scripts which return either 0 or 1. But in the end I don't care what
is returned...

> 
> > 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
> 
> Original, but why not after. It's original to have a fine grained control like 
> this.

I really don't understand what you are trying to say here ;-) Was it a
question or a statement? :-)

> 
> >   Return type:
> >     int    : 0 on success, 1 on error or if performance settings are not
> > 	     supported for the current governor
> 
> Same as above, a boolean looks better to me.
> 
> > 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
> 
> I'm not completely sure about the use on this. Could you elaborate a bit
> more?

With the ondemand governor this setting is set through
/sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load . The
userspace implementation evaluates also the CPU nice load when calculation
the CPU load.

It specifies whether niced processes can cause a CPU frequency increment
although they don't really need that much CPU power and thus wouldn't jump
over the UP_THRESHOLD where frequencies are usually increased.

It's a policy decision. On AC power for example, you also want to conisder
niced processes because if the CPU frequency is switched up more
frequently isn't that problematic. In the other case, On battery, you want
a more passive frequency policy and thus you don't consider niced
processes.


> 
> > 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
> >
> 
> I think one method is missing, I would expect a method to list the available 
> CPU governors.

Yes, this could be added or this information could be exported on a
device.


Regards,
	Holger