Gentoo Forums
Gentoo Forums
Gentoo Forums
Quick Search: in
Undervolting AMD Llano
View unanswered posts
View posts from last 24 hours

 
Reply to topic    Gentoo Forums Forum Index Kernel & Hardware
View previous topic :: View next topic  
Author Message
lexflex
Guru
Guru


Joined: 05 Mar 2006
Posts: 363
Location: the Netherlands

PostPosted: Fri Feb 01, 2013 6:33 am    Post subject: Undervolting AMD Llano Reply with quote

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,
Code:
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.
Back to top
View user's profile Send private message
lexflex
Guru
Guru


Joined: 05 Mar 2006
Posts: 363
Location: the Netherlands

PostPosted: Fri Mar 08, 2013 3:23 pm    Post subject: Reply with quote

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"...)
Back to top
View user's profile Send private message
depontius
Advocate
Advocate


Joined: 05 May 2004
Posts: 3509

PostPosted: Fri Mar 08, 2013 5:06 pm    Post subject: Reply with quote

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.
_________________
.sigs waste space and bandwidth
Back to top
View user's profile Send private message
lexflex
Guru
Guru


Joined: 05 Mar 2006
Posts: 363
Location: the Netherlands

PostPosted: Fri Mar 08, 2013 7:24 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
depontius
Advocate
Advocate


Joined: 05 May 2004
Posts: 3509

PostPosted: Fri Mar 08, 2013 7:42 pm    Post subject: Reply with quote

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.
_________________
.sigs waste space and bandwidth
Back to top
View user's profile Send private message
lexflex
Guru
Guru


Joined: 05 Mar 2006
Posts: 363
Location: the Netherlands

PostPosted: Sat Mar 09, 2013 7:14 am    Post subject: Reply with quote

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 :-) ).
Back to top
View user's profile Send private message
_______0
Guru
Guru


Joined: 15 Oct 2012
Posts: 521

PostPosted: Sat Mar 09, 2013 6:19 pm    Post subject: Reply with quote

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 :/
Back to top
View user's profile Send private message
lexflex
Guru
Guru


Joined: 05 Mar 2006
Posts: 363
Location: the Netherlands

PostPosted: Sun Mar 10, 2013 6:19 pm    Post subject: Reply with quote

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.
Back to top
View user's profile Send private message
Display posts from previous:   
Reply to topic    Gentoo Forums Forum Index Kernel & Hardware All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum