[mythtv-users] undervolting k8

Nick Rosier nick.rosier at gmail.com
Sun Dec 4 09:05:08 EST 2005

On 12/4/05, Marius Schrecker <marius at schrecker.org> wrote:
> Hi,
> As part of noise reduction I'm looking into gently undervolting my
> athlon64 (3700+ san diego), and possibly setting a lower minimum
> frequency. Powernow reports:$ dmesg |grep powernow
> powernow-k8: Found 1 AMD Athlon 64 / Opteron processors (version 1.50.4)
> powernow-k8:    0 : fid 0xe (2200 MHz), vid 0x6 (1400 mV)
> powernow-k8:    1 : fid 0xc (2000 MHz), vid 0x8 (1350 mV)
> powernow-k8:    2 : fid 0xa (1800 MHz), vid 0xa (1300 mV)
> powernow-k8:    3 : fid 0x2 (1000 MHz), vid 0x12 (1100 mV)
> This despite trying to reduce vcore in the bios from 1400mV to 1300.
> What I want is some way to override the pst tables supplied by the bios.
> I've seen some patches around, but none of them are aimed at higher 2.6
> kernels, and I don't feel up to messing about here with things I don't
> fully understand.
> Does anyone know of a patch to 2.6.14 that would let me either hardcode my
> preferred fid/vid  values, or, prefereably, manipulate them on the fly by
> writing new values to /sys (I only see frequency values here, nothing to
> do with vcore)?
> Also, is it possible that this processor supports speeds as low as 800MHz?
> Any pointers appreciated.

The frequency/voltage tables are afaik read from the cpu. I don't
think you can change those. If you want to change the cpu-frequency
(and voltage), you need to compile your kernel with the CPU Frequency
Scaling (Power Management), load the modules and install cpufreqd (or
equivalent tool). This daemon can change the frequency of your
processor depending on your settings (cpu-usage, power/battery,
overheating etc..), e.g. I keep my cpu at 1GHz as long as cpu usage
stays below 60%.


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