[ltp] The zen of power saving, still 21.4W on Thinpad Z61p :(

[Marius Gedminas]

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On Fri, Dec 28, 2007 at 08:10:22PM +0100, Laurent Gilson wrote:
>> This prodded me to look into the humongous power usage of my Z61p some
>> more, and here are all the details I found, along with a plea for more
>> suggestions and help :)
>
> Does the CPU voltage-scaling work? Your CPU should switch to a lower
> voltage if a lower frequency is used. check=20
> /sys/devices/system/cpu/cpu0/cpufreq/
> for more information.
>
> Try fixing the frequency at 1GHz. It will hurt performance... but you will
> not notice it in office. The > 600 switchs from 1GHz to 2GHz are a real=
=20
> killer
> and should be avoided.

Really?  Many people who sounded like they know what they're talking
about suggest otherwise.  Let me search for a quotation...

  Why is "ondemand" kernel's CPU governor more efficient than the
  "conservative" one (or than manually lowering CPU freq)?

  At lower freqs, your CPU may take more time to execute heavy tasks, so
  will spend less time in idle (power saving) state. The "ondemand"
  governor solves this by elevating the CPU to full speed when needed,
  so it can go back to idle state quickly.

        -- http://www.lesswatts.org/projects/powertop/faq.php

I also remember a slide with a complicated-looking physical formula
explaining why running at a higher frequency for a shorter time uses less
power than running at a lower frequency for a longer time.  It might
have been in one of the linux.conf.au videos.

>> This is way higher than most people, and I'm envious of Ted's 10W or
>> less :-/
>
> 9.5 - 10.5W with WLAN here (R51). ~13W is normal.

Nice.

Marius Gedminas

P.S. Hey, I only just noticed that http://www.linuxpowertop.org/results.php
mentions the same laptop I currently have (T61 with Intel graphics)
--=20
I am Lalo of deB-org. You will be freed. Resistance is futile.
                -- from the sig of Lalo Martins

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