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List:       kde-devel
Subject:    Re: Patch: Idea for saving power on laptops
From:       Florian Hackenberger <f.hackenberger () chello ! at>
Date:       2007-05-18 21:42:19
Message-ID: 200705182342.20311.f.hackenberger () chello ! at
[Download RAW message or body]

On Friday 18 May 2007, Randy Kramer wrote:
> On Friday 18 May 2007 10:59 am, Florian Hackenberger wrote:
> > And it certainly saves some power.
> Does it?  I mean, I wouldn't assume that--don't processors have to run at
> certain minimum speeds doing NOPs if nothing else, and RAM has to be
> refreshed periodically even if it is doing nothing.
True, but it consumes less power when doing nothing for longer periods of time 
(frequency scaling being on the same level). See [1] for a reference.

> Did the laptop actually run cooler, or do you have some other objective
> confirmation that power is saved?
I based my statement of subjective measurements. But I just measured the 
effect using the smapi interface to my thinkpad battery (which returns power 
drain measurements from the hardware). Here are the results:
Average over 5 minutes:
with firefox on:
16.48 mW/h
with firefox off:
15.85 mW/h

The following list of websites was loaded (in tabs):
http://www.q12.org/phd-movies.html
http://de.wikipedia.org/wiki/Die_vierzig_Tage_des_Musa_Dagh
http://stefans.datenbruch.de/lafonera/
http://stefans.datenbruch.de/gnucash/gc2latex.shtml
http://forum.openwrt.org/viewtopic.php?pid=6168
http://wl500g.info/showthread.php?t=12&page=2
http://www.artofproblemsolving.com/Wiki/index.php/Asymptote:_Reference
http://www.artofproblemsolving.com/Wiki/index.php/Asymptote:_Useful_commands_and_their_Output
http://www.blogin.it/fonera4.php
I did not check which of them has the misbehaving script on it, but firefox 
causes a constant load of 20% CPU power on my system.

The result is not that much but certainly measurable. My battery has a full 
capacity of 37190 mW. Using the patch would give me 5.38 minutes more battery 
life over about 2.3 hours.

Attached you find a graph and the raw measurements in mW/h (no idea why the 
values are negative btw.).

Cheers

[1] http://acpi.sourceforge.net/documentation/processor.html

-- 
Florian Hackenberger
student @
University of Technology
Graz, Austria
florian@hackenberger.at
www.hackenberger.at

["measurement.eps" (image/x-eps)]
["without_firefox.txt" (text/plain)]

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