Most if not all of the undervolting, underclocking, and monitoring software tools used by SPCRers are for Windows. What equivalent tools are available in GNU/Linux? I am aware of lm_sensors but that is all. Are there any tools to undervolt and underclock other than through the BIOS?
There is the cpu frequency selector applet (/usr/bin/cpufreq-selector) which
will enable you to choose a governor (conservative, on demand, etc.) or
you can lock in a specific speed. This is all from the ACPI info retrieved
from the BIOS, pretty much. No recompiling required.
Undervolting lower than the standard
voltage for a given frequency will
require patching and recompiling the appropriate kernel module (different
ones for various Intel and AMD processor families). I've undervolted
my Merom (T7400), can't speak for AMD processors, but it required
downloading kernel source, applying a third-party patch to a module,
and then because the patch doesn't support Core / Core 2 Duo, adding
a couple of tables myself (straightforward C programming, once you suss out the structure).
Some links on work done with Intel processors, if you want to pursue this further:
Oh, BTW, once lm_sensors is set up, the utility gkrellm
is great for
displaying your temps, voltages, fan rpm, etc.