# Undervolting AMD Llano

## lexflex

Hi,

I would like to undervolt my cpu at low frequencies. 

For this I installed linux-phc,    , but this doesn't support my cpu it seems from the website http://www.linux-phc.org/  .

Also, 

```
modprobe phc-k8
```

Resulted in a segmentation fault.

Is there any other way to change the CPU voltage profile ? 

Thanks for any pointers related to undervolting,

Alex.

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## lexflex

Bump, anyone any idea? 

Maybe it cant be done using software but only from the bios (but then it is a static voltage), but I can't find a definite answer ( also not an "its not possible"...)

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## depontius

Make sure your kernel includes the cpu frequency modulation stuff - ask more questions if you need more info.  I typically make 'ondemand' my default governor, and then make sure you build the right hardware interface.  I don't know if Llano uses powernow-k8, powernow-k10, cpufreq-acpi, or something else.  I believe the governors correctly modulate the voltage.

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## lexflex

Thanks for your reply, 

Indeed I already have the powernow-k8 daemon and cpufreq scaling active.

I was looking for a way to adjust the voltage-scheme related to the specific frequencies, since it appears stock-voltages are still quite high.

linux-phc seems to does something like this, but for different cpu's...

Alex.

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## depontius

There was an additional set of "stuff" added to the kernel in the past 6-9 months.  It looks a lot like the frequency modulation, but carries more overtones of voltage regulation about it.  It's listed under "PM_DEVFREQ" and looks a lot like the old cpufreq stuff. (or "Generic Dynamic Voltage and Frequency Scaling (DVFS) support (PM_DEVFREQ)")  The funny thing is that while there are the usual 4 governors listed, there is a spot for drivers, but non are listed.  I also looked in staging and saw nothing there.  So I'm not sure what's up with this, or if it's what you're looking for.

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## lexflex

Thanks,

I didn't notice that before, I will look into that. It seems indeed to have to do with allowing better userspace control of voltages and frequencies, allthough it is still unclear to me how this works ( searching the web reveals some stuff about DVFS , so I'll start reading  :Smile:   ).

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## _______0

lexflex

I think for llanos the acpi_cpufreq module is better than powernow-k8. Both work but the former apparently is more modern and complete.

I also like this idea about undervolting. If smartphones can do it why not desktops? I don't like the minimal >1.3Ghz or something for desktop. Ideally minimum would be 700mhz or 500mhz.

I know this should work because there are routers running linux at around 200mhz.

Indeed there was a crazy idea about adding an ARM cpu to x86 machines so they can be put in a lower power state.

Why is x86 so inflexible about frequency scalability? I have an AMD proc just with TWO frequencies options :/

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## lexflex

Thanks,

 *_______0 wrote:*   

> 
> 
> I think for llanos the acpi_cpufreq module is better than powernow-k8. Both work but the former apparently is more modern and complete.
> 
> 

 

Ah, indeed I see that now. Tried to modprobe acpi_cpufreq with my 'old' 3.6 kernel and couldn't load it, but after upgrading to 3.7.10 now acpi_cpufreq is the default ( and loaded automatically instead of powernog-k8 it seems).

 *Quote:*   

> 
> 
> I also like this idea about undervolting. If smartphones can do it why not desktops? I don't like the minimal >1.3Ghz or something for desktop. Ideally minimum would be 700mhz or 500mhz.
> 
> Why is x86 so inflexible about frequency scalability? I have an AMD proc just with TWO frequencies options :/
> ...

 

For my AMD A6-3500, the minimum is 800 MHz using the regular governors, so that is a better already. And it works in smaller steps up to 2.4 GHz.

But still, a bit lower with a lower power-consumption would indeed be nice...

I'll try further to see what I can do about the voltage, and post here if I manage to reduce it....

Alex.

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