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omgwtfbyobbq

Member

Registered: 2006-07-04

Posts: 226

Revolting undervolting.

I've tried a patch for 2.6.24 that would've allowed me to set the voltage over on the Gentoo forums, but that just complains about the freq_table and does nothing. I'd like to see how low my Sempron 3000+ can go so to speak. Powernow-k8 for this proc has two states, 1.38V/1.8ghz and 1.1V/1ghz. Is there anything I can do to go lower, like CrystalCPUID under win?

gothmog.todi

Member

From: Austria

Registered: 2007-07-18

Posts: 120

Re: Revolting undervolting.

I didn't try it myself, but maybe cpupw does what you want --> http://tuxamito.com.es/cpupw/index.php

"The main feature is that this daemon will let you change the voltage of the cpu. This let's you do undervoltage (or overvoltage). With undervoltage your cpu will consume less energy so your battery life (if you are using a notebook) will increase and it will run cooler. "

omgwtfbyobbq

Member

Registered: 2006-07-04

Posts: 226

Re: Revolting undervolting.

I don't think it will. cpufreq-set only lets me set those two voltage/speed steps and I'm pretty sure cpupw uses it. I suppose I could always troll the Gentoo forums in order to get some info as to why the patch doesn't work.

gothmog.todi

Member

From: Austria

Registered: 2007-07-18

Posts: 120

Re: Revolting undervolting.

I tried it with my Athlon64 here and was able to set the voltage of the higher frequency steps down to 1.1V. That probably doesn't help you (I take it you want to get to lower levels than that), but I thought I mention it, because I find it kinda neat.

omgwtfbyobbq

Member

Registered: 2006-07-04

Posts: 226

Re: Revolting undervolting.

It does help, since it drops about 25W off of peak load consumption, it's just that like you said I wanted to see if I could undervolt it below 1.1V.

schivmeister

Developer/TU

From: Singapore

Registered: 2007-05-17

Posts: 971

Website

Re: Revolting undervolting.

With NHC in Windows, it's fun. It can be more fun, with Linux-PHC in Linux. Stock kernel, yes.

cat /sys/devices/system/cpu/cpu*/cpufreq/phc_vids

This would definitely show you the current voltage IDs, in steps of 4. This is relative to the 4 clock steps, aka speed steps. The first is of course the max freq, the last being the lowest freq. From Core Duo and up, you cannot set the minimum step lower than the lowest volt assigned to the lowest freq. I'm not particularly sure about AMD dual-cores. For me, I can maintain a stable system with the lowest VID for all 4 steps from 1.6GHz down to 800MHz

19 19 19 19

but for extra assurance I live with

21 21 19 19

From NHC in Windows, I know 19 is 0.75 V for this Core Duo processor You can look up the datasheets for yours to find out the IDs, or basically just go ahead and get agressive by trial-and-error. Pentiums and Athlons before Intel's Core Duo are able to go way below, that's for sure.

Last edited by schivmeister (2008-02-08 01:45:09)

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I need real, proper pen and paper for this.

wuischke

Member

From: Suisse Romande

Registered: 2007-01-06

Posts: 630

Re: Revolting undervolting.

Wow, thanks a lot for this, I didn't know this was in the stock kernel already. I've a 1.6C2D, too and it seems to work very well with lower voltage even at higher clocks - thanks again.

omgwtfbyobbq

Member

Registered: 2006-07-04

Posts: 226

Re: Revolting undervolting.

Unfortunately everything in /sys/devices/system/cpu/cpu*/cpufreq/ only has two states so it's a no go for me. Thanks though!

Edit-I went back to the thread on the Gentoo forums and it turns out I was using the patch incorrectly. At the lowest acceptable voltage, full load power consumption drops to 68Wcompared to around 110W at the usual 1.25V.A patched powernow-k8 ftw!

Last edited by omgwtfbyobbq (2008-02-08 15:17:30)