Problems with power saving on Kubuntu

In my previous post on KDE and Kubuntu’s power consumption I mentioned that Kubuntu and/or KDE’s power consumption seems rather high. Since then I have investigated the problem. All the testing I’m describing here is still done with my Acer TravelMate TimeLine 8371 with the latest 1.18 BIOS, but with the latest Kubuntu Lucid a.k.a. 10.04 and the 2.6.33 kernel from the Ubuntu kernel PPA.

I’ve posted on the KDE forums to ask why I experienced such a high power consumption. With the help from others, I figured out that Kubuntu doesn’t do a good job at power saving because of some bugs. Running PowerTOP on the 8371 gives me the following suggestions to reduce consumption:

• Enable USB autosuspend for non-input devices by pressing the U key
• Enable SATA ALPM link power management via: echo min_power > /sys/class/scsi_host/host0/link_power_management_policy or press the S key.
• An audio device is active 100.0% of the time: hwC0D2 Intel G45 DEVCTG
• An audio device is active 58.6% of the time: hwC0D0 Realtek ALC269
• Disable the unused WIFI radio by setting the interface down: ifconfig wlan0 down

The suggestion for USB autosuspend is affected by bug #136549. Apparently the USB autosuspend is already enabled by the default and PowerTOP shouldn’t suggest changing it at all. SATA ALPM link power management makes a serious difference in power consumption, but for some reason only PowerTOP can change it. The power saving script I created or a manual command doesn’t work, this bug is described in bug #427925. For PowerTOP’s suggestions regarding enabling HD audio power saving because the audio devices are 100% of the time or less active (while no sound is playing at all) I filed bug #521424. Trying to enable HD audio power saving with my power saving script doesn’t work, and PowerTOP can’t do it either because it keeps repeating the suggestion to enable it many times even after you have done so. I believe the phenomenon of KDE asking to remove an audio device, as described in my post on the KDE forums, and here, here, here and here. I’ve seen this question occur a lot right after logging in to KDE, but recently since I’m using Lucid and 2.6.33 I have never or very rarely seen it, I’m not exactly sure. I think bug #509708 is related to this. The last suggestion to disable the unused WiFi radio doesn’t work either, it comes up when I disable the WiFi through the hardware button, but PowerTOP also keeps repeating this suggestion after you hit the key to apply the suggestion.

Problem is that the Kubuntu team isn’t making any effort to fix this bug regarding the audio devices being active 100% of the time or less. It’s a Kubuntu specific bug it seems, but so far my bug report hasn’t even been triaged after a month, even after asking attention for it on the kubuntu-devel mailing list. Being a volunteer myself, I understand that many who volunteer don’t have much time on their hands, but some of Kubuntu’s developers are also on Canonical’s payroll. Sometimes even relatively trivial bugs which are easily fixed take a year or longer to get solved, for example bug #291048 and bug #338285. If it takes months before anyone even responds to a bug report or if there is no response at all, it is demotivating for bug reporters to keep reporting bugs.

If these bugs concerning SATA ALPM link power management and HD audio power saving are still present in the stable release of Kubuntu 10.04 LTS (Long Term Support) I’ll start looking for another distribution which ships KDE 4 and isn’t affected by the problems, Chakra draws my interest. The long battery life of over eight hours was one of the primary reasons for buying my TravelMate 8371 notebook, so I’m not settling for five hours because my favorite distribution, Kubuntu, doesn’t do power saving properly. I’ll make sure to compare the power consumption between Ubuntu, Kubuntu and another KDE distribution again when Lucid Lynx is released at the end of April.