KDE Power Profile scripts : Command Line=YES System Settings=FAIL

[bobwya]

Hi

I was just messing about with my Linux-Mint KDE (Kubuntu 11.10) install. I've got KDE 4.8.2 installed from the backports. Running on my dual core 2.67Ghz Core 2 Duo laptop (which has CPU frequency steps of 800Mhz, 1600Mhz, 2130Mhz and 2670Mhz).

Anyway I've tried to add some simple scripts to my power profiles (basically these change the upper frequency limit for CPU scaling, for each core, with the on-demand governor):

/usr/local/sbin/ $  ls -Ahl
-rwxr-xr-x 1 root root 85 2012-04-17 21:52 cpufreq_highperformance.sh
-rwxr-xr-x 1 root root 82 2012-04-17 21:51 cpufreq_lowperformance.sh
-rwxr-xr-x 1 root root 82 2012-04-17 21:52 cpufreq_mediumperformance.sh
/usr/local/sbin/ $  cat cpufreq_lowperformance.sh
sudo /usr/bin/cpufreq-set -c 0 -u 1.6Ghz
sudo /usr/bin/cpufreq-set -c 1 -u 1.6Ghz
...

Following the ARCH wiki I've carefully added my user to a custom sudor's file to ensure that I can run /usr/bin/cpufreq-set with sudo - without needing a password.

On the command line I can type:

/usr/local/sbin/cpufreq_lowperformance.sh

which works - no sudo password required.

However adding this command to the script run box in KDE / System Settings / Power Management / Energy Saving Settings / On AC Power & On Battery Power does nothing very much at all. The cpufreq-info command shows the same upper CPU frequency (for each core) as before. The rest of the profile settings are loaded and I can see the tray notification for the change from AC power to battery...

Any thoughts? :?:
Bob

[SteveRiley]

I would suggest that it's no longer necessary to adjust CPU frequencies with modern distributions. The kernel now defaults to ondemand, so there's no need to manually configure that. I've researched power management a fair bit and read a lot of the debate. Setting ondemand's upper limit to a lower value (or changing the governor to conservative) doesn't really help save power. In fact, it will cause processes to run longer than they otherwise would, often increasing the total amount of power used to complete the process.

[james147]

Having also looked into this in the past I came to the same conclusion that SteveRiley made, there is no point in changing the frequencies lower to save power, as more power can saved by having the cpu run for less time and be able to sleep again sooner.

[bobwya]

Having also looked into this in the past I came to the same conclusion that SteveRiley made, there is no point in changing the frequencies lower to save power, as more power can saved by having the cpu run for less time and be able to sleep again sooner.

The problem is the thermal envelop on my laptop is not great. That's why I mentioned the upper frequency of my CPU - which is quite high for a mobile Core 2 (Wolfsdale). I can see that the laptop spends a lot of time at 800Mhz... But when it is maxed out doing video encoding or compiling source code it will start going into thermal meltdown. It's useful to be able throttle back the CPU frequency limit when I'm doing this sort of thing for an extended period... The thermals of the notebook are so bad I've had to file down the plastic grill in front of the single metal heatsink - which cools both the Core 2 Duo (Wolfsdale) 2.67Ghz CPU and an ATI 4650M GPU... So my main use for this feature is not to save power and artificial throttling can be useful in some circumstances!!

Anyway like I said I was just playing about trying to get the Power Profile stuff to work - this was not a serious project!! In fact I rarely run my notebook on battery (since the battery life is so crap anyway). Problem is really that what should work, in KDE, doesn't appear to work - and I am not sure why!! What I want to know is not "why I shouldn't be doing this" - but "why what I am trying is not working"!!

Thanks for the responses anyway! Now can someone answer the question I asked
Bob

[james147]

The problem may be that the scripts are being run, but something else is changing the values as well (possibly after your scripts have run). I would look into laptop-mode-tools to see if you can configure that the way you want it.

[whatthefunk]

My power profiles have been broken for months. Nobody listens to me though