Re: Ondemand governor by default in etch
On Thu, Dec 07, 2006 at 05:23:51PM +0100, Hendrik Sattler wrote:
> 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?:
So, broadly speaking, you support doing something like this by default,
just not the ondemand governor?
> "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".
I have yet to see a machine with trouble with this, though that doesn't
say they couldn't exist.
See, for example, Novell's comments here:
http://forge.novell.com/pipermail/powersave-devel/2006-April/000478.html
> > 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 ;)
That is completely useless unless the user has already manually figured
out which cpufreq modules to load, and loaded them.
I tested that before I wrote my article. It doesn't load modules for
you, and nothing else does by default, either. I also grepped through
the source: not an insmod or a modprobe to be found.
That bit is the largest problem anyway.
> > 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
> switching.
If we tweak the parameters so it doesn't switch as fast, probably that
could be solved, yes? Novell seems to believe that ondemand configured
that way is more stable than conservative.
> 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.
I have.
It is also much more invasive than this simple switch, and doesn't
necessarily play nice with Gnome/KDE cpu frequency widgets, etc. Plus
there are n favorite userspace daemons (laptop-mode-tools, powersaved,
powernowd, cpudyn, etc, etc.).
I suggested it this way because it is non-invasive and works with
anything.
> 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.
It makes a noticable difference on my Macbook Pro's battery life. I
don't (yet) have the equipment to measure the power draw of my desktop.
Note that this is not the same as a sleep state. This holds the CPU at
a lower frequency until CPU utilization hits 80% (by default).
-- John
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