Re: USB power usage

Hi!

Couple of watts is not that bad, considering usb still eats 4W more
than it should.

The USB autosuspend mechanism has been present for a while in -mm and is
included in 2.6.20-rc (although you have to turn on CONFIG_USB_SUSPEND,
which is off by default -- it would be nice to change that). Has anybody
tried doing some real-world measurements to see if it actually makes a
significant improvement in power usage?

I did measurements while in -mm, and yes it helped. And yes,
it works in 2.6.20-rc2, too:

root@amd:~# cat /proc/acpi/battery/BAT0/state ; sleep 20; cat
/proc/acpi/battery/BAT0/state ; sleep 20; cat
/proc/acpi/battery/BAT0/state ; sleep 20
present: yes
capacity state: ok
charging state: discharging
present rate: 14245 mW
remaining capacity: 50020 mWh
present voltage: 15793 mV

(turned off bluetooth hanging off USB here).

present: yes
capacity state: ok
charging state: discharging
present rate: 11650 mW
remaining capacity: 49940 mWh
present voltage: 15830 mV
present: yes
capacity state: ok
charging state: discharging
present rate: 10935 mW
remaining capacity: 49870 mWh
present voltage: 15826 mV
root@amd:~#

As you can see, it saves ~3.5W, which is huge deal on machine that
eats 11W total.

(X60 owners, get 2.6.20, and _disable that bluetooth_ while not in use).
Pavel

--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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