linux-kernel - Re: USB power usage

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Message-ID: <20061226144008.GA2062@elf.ucw.cz>
Date:	Tue, 26 Dec 2006 15:40:08 +0100
From:	Pavel Machek <pavel@....cz>
To:	Alan Stern <stern@...land.harvard.edu>,
	kernel list <linux-kernel@...r.kernel.org>
Cc:	Linux-pm mailing list <linux-pm@...ts.osdl.org>
Subject: 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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