Re: [PATCH 2.6] update passive cooling algorithm

Dominik Brodowski
2004-01-12T17:39:22Z

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On Mon, Jan 12, 2004 at 04:46:11PM +0100, Ducrot Bruno wrote:
> On Sun, Jan 11, 2004 at 10:12:55PM +0100, Dominik Brodowski wrote:
> > [Len, could you test and verify this patch, and push it to Linus, please?]
> >
> > The current algorithm used by Linux ACPI for passive thermal management has
> > two shortcomings:
>
> ...
>
> > +/* If a passive cooling situation is detected, primarily CPUfreq is used, as it
> > + * offers (in most cases) voltage scaling in addition to frequency scaling, and
> > + * thus a cubic (instead of linear) reduction of energy. Also, we allow for
> > + * _any_ cpufreq driver and not only the acpi-cpufreq driver.
> > + */
>
> Just a stupid question:
>
> What is best if processor heat issues (apart turning on the fan)?
>
> Reducing voltage of the processor, but still allowing it to run execution
> at 100% (which is the case if the processor is heating), or reduce
> amount of time allowed for the processor to execute?

voltage scaling. It offers a much better (quadratic) saving than clock
modulation (linear saving). Doing both [and you need to do it, as the CPU
won't run with fewer volts at the same frequency] gives you cubic savings.

Dominik

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