CPU freq scaling

Ken Moffat ken at linuxfromscratch.org
Sun Oct 7 16:48:36 PDT 2007

On Sat, Oct 06, 2007 at 05:59:50PM -0700, Walter Barnes wrote:
> Hello, 
> I've just finished building LFS 6.3 and have started adding a few extras for my laptop (Fujitsu Lifebook, C Series). After reading Ken Moffat's cpufreq hint I've succesfully set up my system to use the conservative freq governor but I have a few questions... 
> First, I've temporarily commented out the command to set ignore_nice in the boot script as it does not work. In particular, this path does not exist: 
> /sys/boot/devices/system/cpu0/cpufreq/conservative/ignore_nice
> Should it instead be:
> /sys/devices/system/cpu/cpu0/cpufreq/conservative/ignore_nice_load     ?
 Keep a view of what matters - if your chosen governor _works_ (e.g.
in one term try untarring, then run configure and make - does the
frequency change as expected ?) then you are fine.  I haven't been
active in development recently (hoping to get back soon, but in the
meantime I've found other interests to take my time), and I confess
I haven't checked my most recent build to see if frequency scaling is
actually working (of 4 current available desktop boxes, 2 don't do
scaling, and 1 - a ppc64 - needs powernowd).

 Unfortunately, /sys seems to be forever changing - what worked 2
releases ago might have been renamed by now, so if it _isn't_
working, try using the different path to ignore_nice_load and see if
that helps.  ISTR that the logic was reversed at some point, so it
might not be necessary.
> Also, there are several files under the conservative directory that, from their names, seem to control the freq govenor's behavior. Can someone point me to docs that expain what these files are and how to use them?
> Finally, my host system (Knoppix) can underclock my Pentium M (Dothan). The contents of the <cpufreq-path>/scaling_available_frequencies includes 400Mhz and 200Mhz. These are not present when I boot my LFS system (lowest is 600Mhz). Could someone also point me to any docs that expain how to do underclocking?

 Wild guess - the Knoppix kernel is quite a bit older than the LFS
kernel ?  On intel systems, cpufreq seems (from idle observation of
lkml) to be increasingly tied to what the bios/acpi makes available,
so now fewer frequencies are marked as valid (something to do with
acpi, and possible damage if the frequency isn't really valid).  The
kernel doesn't officially support running outside the 'legitimate'
frequencies.  I don't have any recent intel systems, so I haven't
needed to understand the problem.  Maybe try google, particularly for
gentoo or fedora bug reports.

 As to finding docs on any of this, I hope someone can find a good
url, because it's always nice to find good documentation on using
less power.

das eine Mal als Tragödie, das andere Mal als Farce

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