Hi,
I own an Compaq Presario 920EA laptop with an Athlon XP 2000+ mobile
processor. It uses AMD's PowerNow! speedstepping technology to
preserve
battery power when the system load is low. This works just fine in
Windows XP since there is a driver (amdk7.sys) for the CPU feature,
but
I don't think there is one for Linux (??). I would like to install
Gentoo on my laptop (I have gentoo on all my other desktop PCs), but
if
that results in an ever-running (and noisy!) CPU fan and short battery
life time, I need to think twice about it. What's the state of the
PowerNow! technology on Linux kernels (2.4 series) ? If there is
support, does it scale automatically, like in Windows, based on system
load ? This is really the only thing stopping me from installing Linux
on my laptop.
I'm using "enhanced speed step" on a pentium-m on my laptop. It works pretty well. I'm using 2.6-test kernels now, however, but it worked on my 2.4.22-preX-ac kernels back when i had them around.
As stated, you must manually set the cpu speed if you wish to change it. This is done by echo'ing values into the /proc filesystem on 2.4, or echo'ing (different) values into the /sys filesystem on 2.6.
As for dynamically changing cpu load based on factors such as load, ac- power status, battery remaining, and so on, the kernel doesnt do that. That is (and should be, i think) handled in userspace by daemons such as cpufreqd.
If in doubt, check out the cpufreq documentation in the kernel source.
--
Chris I
Waste not fresh tears over old griefs.
-- Euripides
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