[ltp] X61 power consumption

[Leszek Koltunski]

Hello everybody,

I run Debian unstable in a X61 ( 2.4 Ghz Core2Duo, 3GB RAM, 4965 wireless, 
965GM graphics ) with the newest BIOS ( updated couple of days ago, 2.16 
IIRC ) Kernel 2.6.26-1-686 ( standard Debian kernel with no patches ).

First, let me say that I am quite happy with this laptop, almost 
everything works out of the box. ( you can read my story at 
http://koltunski.pl/blog/?p=12 )

The past few days I've been reading thinkwiki and this mailing list in an 
attempt to lower my power consumption.  I managed to set it up so mild 
usage ( brightness 50%, wireless on with mild browsing, composing an email 
etc ) eats up about 12.5-13W, which is great considering I started out 
with 16W.

However, yesterday I did the following:

- boot the laptop into single user mode
- lower brightness to the min ( echo 0 > /proc/acpi/video/VID1/LCD0/brightness )
- switch off bluetooth & wireless ( rfkill ) and unload the modules
- unload uhci, ehci, ohci1394, ieee1394, yenta_socket & all pcmcia stuff 
- switch parallel, serial, WOL off in BIOS
- mount partitions with noatime, commit=600 ( iotop confirms there's no disk activity )
- enable SATA powersaving ( echo min_power > /sys/class/scsi_host/host0/link_power_management_policy )
- switch off the fan ( echo level 0 > /proc/acpi/ibm/fan )   ( thinkpad acpi is loaded with fan_control=1 )

In short, I did everything I could think of to go down with power 
consumption as low as I can get. ( let me know if I missed something ).

Then I unplugged the laptop and run powertop 1.10. Results:

powertop reports the CPU is running 99.9% of the time in C6 with average 
residency close to 700ms, there are about 1-1.5 ( and sometimes even 0.8 ) 
wakeups per second, which is great. I dont think that can get any better.

I let it stabilize while not touching the keyboard. The lowest momentarily 
power draw I have seen was 10.0W , and most of the time it was more like 
10.5W.

Then, I rebooted to Windows XP, turned the brightness down as low as I 
could, and set everything to 'conserve energy'. The Windows power thingy 
hovered around 8.5 W, and at one point I've seen even 8.11 W.

The question is: how come single-user Linux (with all the tricks I could 
think of! ) is still using 2W more than Windows XP after 5 minutes of 
hasty configuration? Anyone can explain that?