Power trends

Matthias asked me the other day if I could do a longitudinal study of power consumption of Fedora. I used my new T61 with Intel graphics for the study as this is the machine I use every day. Anything older than F8 failed to boot (SATA?) and so the results are a little short. I will repeat the same test on some older hardware when I have a spare couple of hours next week.

So, what can you take from this graph:

  • When suspend works well, it uses hardly any power
  • Playing high fps-movies fullscreen is bad for your battery.
  • Anything involving large amounts of hard-drive and CDROM accesses will drain your battery.
  • You can save about 4W by turning your brightness down, and 10W by turning the panel off completely.
  • As a trend, linux seems to be getting better at this powersaving thing.

Note: F9 starts with the brightness less than 100% due to a kernel/hal/userspace bug.

So my personal 400ft conclusions:

  • We should dim on idle by default, and turn this option on even when on AC power
  • We should make suspend and resume faster so we can automatically sleep and resume when idle.

I’ve also been playing with other powersaving techniques like knobbling dirty writeback, noatime, ALPM, changing the screen refresh rate and also powering down cores on a CPU. I’ll blog about these later.

If you are interested in this sort of stuff, I’m presenting at the Red Hat summit next week in Boston with a paper titled “Laptop power management”.

11 responses to “Power trends”

  1. Qball

    what I notice on my thinkpad, is that unloading the infrared modules saves alot of power. Same goes for unloading the wifi driver (even with wifi disabled in networkmanager, it still takes extra power).

    This way I am able to get a 10-11W usage from my laptop (ibm t42, 1.7ghz, 7200rpm disk, 1400×1050 15.4″ screen). I manage to get it slightly below 9W by removing the bay, switching to console instead of X etc..

    during real work™, I get around 12-14W. I also notice that average power usage does not differ alot if I force my cpu to 600Mhz, or let it step up and down. The last feels alot better from user point of view.

  2. Petrosyan

    Shouldn’t power consumption in hibernate mode be exactly 0?

  3. qhartman

    I’d love it if you would post your slides, and consider recording the presentation. There’s no way I can get to Boston (living about 1500 miles away…) but I am keenly interested in this topic and would love to hear / see more on your findings.

  4. troll

    Don’t dim on idle. Often, the computer is idle and the user is watching something, ie. reading something really hard to comprehend and pondering about it. Dimming absolutely kills usability at that point. Furthermore the difference between minimum and maximum is clearly nothing as even your chart shows us.

  5. Anders Aagaard

    Do dim on idle, and count idle as screensaver being on. Seems fairly fool proof to me.

    Do you suspend to ram? If so, you could suspend when idle, for me atleast resuming from suspend takes 2-3 seconds, so I dont mind waiting that to decrease power usage. I got a little python script that suspends when the screensaver comes on, if my load average is low and amarok isn’t playing music :p

  6. oliver

    “So, what can you take from this graph:”

    Sorry, but first thing to take from this graph is that OpenOffice (it _was_ made with OOo, right?) apparently sucks at making graphs :-)
    – why is in the color explanation (F8, F9, Rawhide) the order of colors exactly opposite from the order of the bars? That’s highly unintuitive.
    – why are there _no_ lines right at the 10W, 20W, 30W, 40W marks, instead of drawing _thick_ lines there?
    – the text rendering on the left (Hibernate, Suspend…) looks really broken.

    Of course, the graph’s contents are really interesting :-) and btw. thanks for the great g-p-m – even on eeepc with its quite broken battery it gets meaningful “remaining time” estimates.

  7. baze

    what do you suggest for using speedstep on a c2d for example? preferably sth that “just works” and doesn’t require lots of configuration… just using g-p-m doesn’t reduce cpu speed, does it?
    and are laptop-mode-utils actually good or is the constantly spinning down the hdd killing it slowly?

  8. Alex Hixon

    How much battery life do you get out of the laptop on average?

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