[sclug] Under(re)volting - How does MS do it?

Alex Butcher lug at assursys.co.uk
Thu Mar 1 10:18:20 UTC 2007

On Thu, 1 Mar 2007, Roland Turner (SCLUG) wrote:

> On Wed, 2007-02-28 at 22:52 +0100, Pieter Claassen wrote:
>> So, the question is simply: How come Microsoft manages to get around 6
>> hours out of this battery (urban legend) while the best I can do (after
> CPU halting and screen dimming?

Most modern distributions configure cpuspeed or gnome-power-management as
standard so that frequency scaling works out of the box. Something that the
kernel devlopers have pointed the finger at in the past has been the kernel
100Hz or 1000Hz tick. I believe the answer to this is to move the kernel to
a 'tickless' design. Work is ongoing, but it's not ready yet. Recompiling
the kernel to use 100Hz instead of 1000Hz *may* improve battery life.

> Spinning down the HD?

Pieter mentioned he's using laptop-mode, which in conjunction with the
support scripts <http://www.samwel.tk/laptop_mode/>, does this already.

> (As Alan suggests: you do have empirical evidence that 6 hours is
> actually possible, right?)
>> manually disabling wireless, unloading USB drivers, enabling laptop
>> mode) is only 2 hours? Yes, I know P=V^2/R which I suspect that even a
>> minor drop in board voltage will have significant power gains. However,
>> everything I read warns me against patching the kernel for undervolting
>> because of possible hardware damage (motherboard not chip).
> _Hardware_ damage? That seems rather unlikely.

That's what the developers of the patch warn:

> - Raz

Best Regards,
Alex Butcher, Bristol UK.                           PGP/GnuPG ID:0x5010dbff

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