Linux laptops, revisited (can any sleep like my PowerBook does?)

Michael L Torrie torriem at chem.byu.edu
Mon Jan 21 10:44:43 MST 2008


This thread has been enlightening, to say the least.  But not super
encouraging.  What I'm getting from this thread is that suspend to ram
is possible on some laptops.  But it may require some assembly.
Furthermore from what Thinkpad owners have told me (this extends to all
Linux laptops from what I can see) that battery life is well below
Windows XP on the same machine.  3 hours is considered "good" for a T61p
with a 9 cell battery.  So for a variety of reasons, many of which would
seem to be beyond our control as Linux hackers, power management on
Linux just isn't there yet.  This point of view, according to a slashdot
comment criticizing me, is FUD, but oh well.

I recently started playing a bit with Powertop[1].  For fedora or ubuntu
users I'm sure it's in the standard repositories.  Using powertop is
very interesting.  I recommend that anyone with Linux on their laptop
install it and see what it says.  It will track power usage (when not on
AC power), CPU states, interrupts and so forth.  On a desktop machine
you'll not get power usage statistics, but you will get interrupts per
second and the cpu states.  My AMD desktop machine was very interesting.
 The NVidia binary drive woke up the CPU between 60 and 100 times a
second.  On a laptop this would really affect battery life.  Also my CPU
never once reached the "C3" state, which on a laptop is where your cpu
should be spending 80% of its time, in battery conservation mode.  So
obviously my desktop machine is a power hog.  If any of you are running
the NVIDIA drivers on a laptop, there is an xorg.conf setting that you
can use to disable the VBLANK interrupt, except when it's demanded.
This reduces the number of CPU wake-ups pretty dramatically.  Also
powertop can recommend a number of things, like setting the sleep (as in
idle) mode on the usb drivers, the audio drivers, etc.  Someone claimed
that they were able to get a Gnome desktop down to 5 wake-ups per
second.  Judging from my own Gnome desktop they must have disabled every
 little thing, but still.

Anyway, I appreciate the feedback.  Looks like I'll be holding off on my
decision for a while yet.  Leopard will run on my PB 12", so we'll see
how that goes for now.

Michael


[1] http://www.lesswatts.org/projects/powertop/



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