Power Crisis and Linux... Saving power with linux

[ME]

On another completely new topic...

For those of you that have not committed yourselves to compiling your own
kernel, this may offer yet another reason to do it:

Newer hardware (not just laptops anymore) support more in the way of "APM"
(Advanced Power Management) and Linux kernels can be compiled with APM
support.

Simpler uses of APM include being able to the that nifty software shutdown
of power many newer PCs have offered that is like the Macintosh
"Shutdown" for many PowerMac series models and later. This may allow you
to shot down your machine remotely - of course restarting it might be a
problem when you are remote if you did a 
# shutdown -h now
;-)

Copying directly from "Configure.help" in linux/Documentation/ :

CONFIG_APM
  APM is a BIOS specification for saving power using several different
  techniques. This is mostly useful for battery powered laptops with
  APM compliant BIOSes. If you say Y here, the system time will be
  reset after a RESUME operation, the /proc/apm device will provide
  battery status information, and user-space programs will receive
  notification of APM "events" (e.g. battery status change).

  If you select "Y" here, you can disable actual use of the APM
  BIOS by passing the "apm=off" option to the kernel at boot time.

  Note that the APM support is almost completely disabled for
  machines with more than one CPU.
   (Note from ME: that is a good bit to know for you SMP people)

  Supporting software is available; for more information, read the
  Battery Powered Linux mini-HOWTO, available from
  http://www.linuxdoc.org/docs.html#howto .

  This driver does not spin down disk drives (see the hdparm(8)
  manpage ("man 8 hdparm") for that), and it doesn't turn off
  VESA-compliant "green" monitors. 
...

For the longest time, laptops were some of the only bits of PC hardware
that could really gain from APM enabled kernels. Now things are starting
to change.

There are some risks with this. Your new kernel may not like your bios and
freeze during boot.

As mentioned above, hdparm may be used to tune your hd to go to sleep
after a specific time of inactivity. It is probably a package in redhat,
and is a package with debian. (Not all drives have support for power
states and access to them with hdparam.)

Most screen savers do not tell the monitor to go to sleep, but instead
just try to help avoid "burn-in" by changing the images. Turning off a
monitor when you will be gone for extended periods of time is a good way
to save power manually.

The amount of power you can save with APM and turning off a monitor is not
a whole lot when compared to a hair dryer (800-1600 watts) or a Microwave
(400-1400 watts), but it will likely save more power than unplugging that
extra VCR that is powered off but flashing 12:01am. (Mine do this - not
because I dont know how, or am too lazy, but because I do not have cable
and the clocks only purpose before was to schedule recordings - but that
is off topic.)

The CPU box with an HD running and other accessories (not counting
monitor) seems to range on average from ~180watts to about 350 watts for
most systems.

"Green" monitors power consumption can vary a great deal. older monitors
tend to use more power than new ones. Larger ones tend to use more power
than smaller ones. Amount of power used by larger diagonal measurements on
screens is not a simple linear/algebraic increase in power the amount of
power consumed is a modified geometric increase  partly due to surface
area increasing faster than the linear increases in diagonal
measurement. (A~=xy ~=(1.3y)(y)~=1.3y^2) not exact, but an estimate with
ratios assumed.)

15" monitors ~110-300 watts, 17" monitors 180-400 watts, 19" monitors
220-600 watts. (Approximations have wide ranges for above mentioned
reasons as well as different vendors systems for measuring monitor sizes.)

If you are lucky, you may be able to save from 10% to 40% chassis/CPU
power with a combination of APM support on APM compliant hardware that
works with Linux and hdparm set up to deal with a hard drive. (Laptop
power savings can be more due to the inclusion of the LCD and some with
backlight control.)

You should probably research this on your own, but this does give you an
excuse to do more tinkering with your linux kernel. When you mom, wife,
sig-o, etc asks you why you have your nose back at the computer screen,
you can let them know you are trying to save power! ;-)

(Of course if you are like me, you don't need an excuse to work with
linux. :-)

-ME