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Re: Ondemand governor by default in etch

Am Donnerstag 07 Dezember 2006 16:36 schrieb John Goerzen:
> I believe that we should enable CPU frequency scaling, and the ondemand
> governer, by default in etch.

Did you read the kernel help for it?:
"The support for this governor depends on CPU capability to do fast frequency 
switching (i.e, very low latency frequency transitions)."
The most important word is "very".

>  * Is compatible with almost all modern hardware, and just won't
>    load on machines that don't support it
>  * Requires only a 10K ondemand module and a 5-15K driver module to be
>    loaded into the kernel
> Why should it be the default?

It shouldn't.

> Earlier this morning, I wrote up the procedure [1] to enable CPU
> frequency scaling and the ondemand governor.  It's about 3 pages, and
> not even newbie friendly at that.  So the first reason is that people
> that don't know about this feature aren't prone to find it, and even if
> they find it, they aren't prone to know how to enable it.

apt-get install cpufrequtils
cpufreq-set -g ondemand

Really hard ;)

> Secondly, the ondemand governor is very non-invasive.  It requires no
> userspace daemon.  It makes a negligible impact on performance.  And if
> people do wish to run a userspace daemon, this default will not
> interfere with it.  I've tried it all over the place.  It is stable and
> reliable.

I already had a system go off with it. Ok, it didn't have low latency 

> Thirdly, it is ethically the right thing to do.  Think about all the
> thousands (millons?) of machines that are running Debian.  If we save
> even an average of 10W per machine, we could be talking about huge
> energy savings worldwide.  We save our users money on their power and
> cooling bills.  We reduce air pollution, which has been shown to have
> negative health effects.  And we reduce greenhouse gas emissions.
> I can't see any reason NOT to do it.
> How would we turn it on by default?

You REALLY should take a look at laptop-mode-tools.
They can do this for you including loading the proper modules when needed and 
LOTS of other energy saving technics.

And you should take a look at the "conservative" governor, too.
And BTW, did you measure the power savings? My WLAN card and monitor backlight 
eat _all_ the savings and the kernel usually knows how to put the processor 
to a sleep state.


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