Power consumption with Fedora

Owen Taylor otaylor at redhat.com
Tue Dec 2 16:33:48 UTC 2014

Hi John, 

Power consumption is definitely an area that Fedora can improve, and an
area where we've begun to do some investigation.

Measuring battery life is hard, because when power saving is working,
battery life depends so much on what the user is doing. Many
manufacturers don't even provide battery life in their specifications
or at most, provide a rough figure like "battery lasts up to 10 hours".
Doing what?

I've begun writing a test suite that will simulate events of "typical
user activity" (web browsing, word processing), so that we can at least
know machine-to-machine or Fedora-version to Fedora-version how well we
are doing with battery life. Comparing with a different operating system
is hard, since we typically have no idea how claimed numbers are

The second part of trying to improve power management is getting an
understanding of what actually uses power. powertop is impressive, but
can't always be taken at face value. I have some idea that we could
build up a database (or at least a wiki page or two) with detailed
information on power usage for a few representative models so that we
can get an idea about how we need to modify the system software.

On my laptop (ASUS ux301la), various things surprised me:

 * The backlight eats a ton of battery - 4W for the display backlight
and 1W for the keyboard backlight. If you are getting poor battery life,
turn off the keyboard backlight and turn the screen down. But how do we
fix this for all users? We used to be much more aggressive about screen
dimming in GNOME, and it was really annoying. Can we find some happy

 * Although most of the "tunables" in powertop did little that could be
measured, the "Enable SATA link power management" tunable saves 2W(!) We
need to consider whether this should be enabled by default, at least on

 * The next big offender on my system was inactive tabs with Flash ads
in them. If I have nytimes.com open on my system, that's another 2W. How
do we fix this for all users? Can we suspend plugins if there's no audio

This topline stuff is huge for battery life - on my laptop it makes a
difference between around 3 hours and around 7 hours. The rest is hard -
many small things that individually contribute just a little bit. Plus a
baseline of things like DRAM refresh that are fixed.

Having detailed data for multiple laptops (and definitely Macbooks are a
interesting target) would help us make sure that Fedora does a good job
out of the box. I don't think literally just including a set of scripts
that tweak a bunch of things is something we'd want to do, but
understanding what they are tweaking and how that affects power usage
would be incredibly useful.

- Owen

More information about the devel mailing list