Improving Battery Life in Ubuntu Precise 12.04 LTS (part 2)

Last month I wrote about the investigations being undertaken to identify any suitable power savings for Ubuntu Precise 12.04 LTS.  Armed with a suitably accurate 6.5 digit precision Fluke digital multimeter I worked my way through the Kernel Team Power Management Blueprint measuring many numerous configurations and ways to possibly save power.

A broad range of areas were examined, from kernel tweaks, hardware settings to disk wake-ups and application wakeup events.

Quite a handful of misbehaving applications have been identified ranging from frequent unnecessary wake-ups on poll() and select() calls to rather verbose logging of debug messages that stop the disk from going into power saving states.

We also managed to identify and remove pm-utils power.d scripts that didn't actually save any power and even consumed more power on newer Solid State Drives.    By carefully analysing all the PowerTop recommendations we also identified a subset of device power management savings that are shown to be useful and save power across a wide range of machines.   After crowd-source testing these tweaks we have now added them into pm-utils for Ubuntu Precise 12.04 LTS by default.  I'm very grateful to the Ubuntu community for participating in the testing and feedback.

I've written a brief summary of all the test results, however, the full results can be found in the various subdirectories here.   I've also written a very simple set of recommendations to help application developers avoid mistakes that lead to power wasting applications.

We've also set up a Power Management Wiki page that has links to the following:

* Identifying Power Sucking Applications
* Aggressive Link Power Management call for testing
* PCIe Active State Power Management call for testing (now complete)
* Updates to pm utils scripts call for testing (now complete)

..and probably the most useful:

* Power Saving Tweaks

The Power Saving Tweaks page lists a selection of tweaks that can be employed to save power on various machines.  Unfortunately with some hardware these tweaks cause lock-ups or rendering bugs, so they cannot be rolled out by default unless we can find either a definitive list of the broken hardware or a large enough whitelist to enable these on a useful set of working hardware.  Some of the tweaks cannot be rolled out for all machines as users want specific functionality enabled by default, for example, we need to enable Bluetooth for users with bluetooth keyboards and so it is up to the user to chose to disable Bluetooth to save 1-2 Watts of power.

I've also set-up a PPA with a few tools to help measure power and track down misbehaving wake-up events and CPU intensive applications.  These tools don't replace tools like PowerTop and top, but do allow me to track trends on a system over a long running period.   You may find these useful too.

We also have a Ubuntu Power Consumption Project set up to help us track bugs related to power consumption issues and regressions.  

Last, but no way least,  I'd like to thank Steve Langasek and Martin Pitt for all their help with the pm-utils and various fixes to power sucking applications.