Controlling power consumption in linux

ryboto · Post by **ryboto** » Wed May 30, 2007 7:26 am

I've recently stepped back into the linux arena(ubuntu) with the sole purpose being SMP folding. Originally my system was overclocked, but now, I'm trying to run the Opteron at stock, 2.0ghz, and undervolted to 1.1v(the lowest my newer motherboard will allow). The issue here is that the lowest vcore my BIOS will allow me to set is 1.35v. In Windows, CrystalCPUID, with or without CnQ enabled in the BIOS, I can select a vcore manually. It gives me a list going all the way down to 0.8v, but setting anything below 1.1vcore only results in an actual vcore of 1.1v(as monitored by Everest). I can set this vcore, but as soon as I restart my system it is reset to 1.35v, really finnicky motherboard.

With load temperatures of 31C with the undervolted cpu, I'm even considering attempting a fanless configuration, maybe a positive pressure system. Regardless, I still have the task of attempting to lower power consumption in linux. I don't see a point in folding with my system if I can't use the minimum power required to do so, it's wasteful, and now that I'm moving, I wont have the spare change to afford it.

I'm looking for some way, a program, a project, to independently change the voltage to the processor. I've read through this thread, but it's a year old, and like the OP, I'm not extremely versed in linux. I can follow a howto, but I haven't gotten back into it full swing. So, are there any projects out there, or is it all non-configurable and integrated into the kernel? I'm using Ubuntu Feisty.

Thanks!

Palindroman · Post by **Palindroman** » Wed May 30, 2007 10:13 am

Hi, does this help?

qviri · Post by **qviri** » Wed May 30, 2007 10:44 am

Palindroman wrote:Hi, does this help?

That's just a C'n'Q guide - doesn't mention anything about undervolting.

Ubuntu Feisty speedstepped my Pentium M out of the box, but I haven't gotten around to undervolting it yet. I have a friend who knows how to do it, though. I'll report back when I get it working.

ryboto · Post by **ryboto** » Wed May 30, 2007 11:41 am

qviri wrote: Ubuntu Feisty speedstepped my Pentium M out of the box, but I haven't gotten around to undervolting it yet. I have a friend who knows how to do it, though. I'll report back when I get it working.

thanks for the reply. Ubuntu was able to control my cpu out of the box, the reason I think I was seeing instability, as I had been running an overclock. I removed the powernowd package. I don't think ubuntu is actively throttling my cpu anymore, but I have no idea on how to check it, since lm_sensors doesn't read from my motherboard correctly, I can't monitor voltages or frequencies.

edit: i do however have a kill-a-watt meter, and so far, I've confirmed that the power consumption is ~40W less in windows when I undervolt compared to running stock in linux.

floffe · Post by **floffe** » Wed May 30, 2007 12:25 pm

Code: Select all

cat /proc/cpuinfo | grep MHz

in a terminal to see CPU speed (and yes, it should change if you use C'n'Q to underclock).

ryboto · Post by **ryboto** » Sun Jun 03, 2007 8:54 am

guess for now I'll just stick to vmware-ubuntu in windows.

matt_garman · Post by **matt_garman** » Sun Jun 03, 2007 2:40 pm

As far as I can tell, there aren't any "user friendly" apps for undervolting your CPU with Linux. I just did a bit of research, and it looks like, at minimum, you'll have to recompile your kernel.

There's a long thread on the Gentoo Forums that may be of interest to you.

The Linux-PHC (Processor Hardware Control) allows you to undervolt a Pentium M processor (but they don't yet have support for AMD CPUs).

Also, I found this Gentoo HOWTO on Undervolting a Pentium M. Again, not too helpful for your situation, but at least it gives you some background.

So, short answer: I can't seem to find an "easy" way (like the Windows programs you mentioned) for undervolting your CPU in Linux. But it can be done, depending on much work you want to do.

Another idea is to use the Cool'n'Quiet functionality with the "powersave" governor. This will put your CPU in its lowest power state (but also scale back the frequency as well). I know, it's not optimal, as you won't get anywhere near your CPU's rated performance, but it may be a compromise.

Good luck... if you do decide to hack your kernel to support a lower vcore, report back here (or another Linux forum)!

Matt

jaganath · Post by **jaganath** » Sun Jun 03, 2007 3:20 pm

changing CPU vcore in Linux is nigh-on impossible,my solution was to get a motherboard that offered BIOS undervolting.

ryboto · Post by **ryboto** » Sun Jun 03, 2007 4:06 pm

jaganath wrote:changing CPU vcore in Linux is nigh-on impossible,my solution was to get a motherboard that offered BIOS undervolting.

yea, that would be an easy way to go. I don't really think I'm ready to recompile the kernel. I'll be on the lookout for new options though.

jojo4u · Post by **jojo4u** » Tue Jun 05, 2007 10:05 am

The next major release of Linux-PHC wants to add support for the acpi-cpufreq driver, a generic driver which supports Intel CPUs.

b3nbranch · Post by **b3nbranch** » Tue Jun 05, 2007 2:32 pm

matt_garman wrote:As far as I can tell, there aren't any "user friendly" apps for undervolting your CPU with Linux. I just did a bit of research, and it looks like, at minimum, you'll have to recompile your kernel.

The Linux-PHC (Processor Hardware Control) allows you to undervolt a Pentium M processor (but they don't yet have support for AMD CPUs).

Also, I found this Gentoo HOWTO on Undervolting a Pentium M. Again, not too helpful for your situation, but at least it gives you some background.

Matt

Again, it won't help the AMD folks, but you can undervolt with Linux-PHC
for Pentium-M and, with some added table entries in speedstep-centrino.c,
Yonah/Merom processors. I now have my Merom T7400 undervolted from
a standard of 1.21 volts to 1.05 volts. this thread helped a lot. You need to recompile only one module, not
the entire kernel.