Undervolting the Atom for less heat, more battery life.

I am running Ubuntu 8.04.1 and using the acerfand script, and it works great. I have also played around with undervolting and after some testing it makes a difference to heat and power usage, at high CPU usage anyway.

I tested with burnMMX, running 2 instances to max out the CPU. Powertop to check power use, and the acerfand script to check tempurature.I have my fan set to kick in at 65 degrees, and turn off at 55.

Without undervolting tested temp and power usage with powertop.

Power = 12.4 watts avg over 5 minutes
Temp ranged between 65 - 68 degrees, even after the fan kicked in.

After I undervolted, things got better.

When set to 12:24 10:17 8:10 6:3
Power = 11.3 watts avg over 5 minutes
Temp ramped up to 65, but after the fan kicked in it drops down to 61 - 63 degrees.

When set to 12:17 10:17 8:10 6:3
Power = 11.0 watts over 5 minutes
Temp ranged between 60 - 63 degrees.

It doesn't save power at 800MHz, but 1.1 watts and 4 degrees while in high CPU usage is worth the few minutes to set up PHC undervolting in my opinion.

If you are using ubuntu here is a great tutorial
http://ubuntuforums.org/showthread.php?t=786402

Then I put this into my /etc/rc.local

Code:

echo "12:17 10:17 8:10 6:3" > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls
echo "12:17 10:17 8:10 6:3" > /sys/devices/system/cpu/cpu1/cpufreq/phc_controls

If anyone tries this please leave feedback.

 

Any idea how much this helps battery life?

Cheers,

Allan

 

Does undervolting have influence on the performance of the Atom? (both in theory and practice)

 

no, undervolting too much will cause the cpu not to work, so most cpus draw a bit more volts as the have to (just to be on the save side).
what would cuase the cpu speed is the fsb. is the core undervoltet too much, ud have to lower the fsb which causes the cpu to be slower. on the other side, if u would want to make it faster, ud need to set a higher fsb, which would need to overvolt the cpu (thats why all those overclockers need such amazing heatsinks ,p)

(sry for my poor english ;p)

 

At idle with lowest screen brightness I get 7.1 - 7.4 watt.
At highest brightness it's around 9.5 or something I don't recall exactly.
When working with documents + browsing at lowest brightness right now it goes up and down between 8 and 9 watts usually.

I like this idea of undervolting and will look more into it (i would love to get under 7 watts!) but for you, maybe you should look at tweaking other places first?
EDIT: I see now it wouldn't work at 800 mhz...

But maybe you're measuring consumption when running heavy apps/doing other fancy stuff I don't know...

 

PHC works on my AA1 with the latest kernel from sickboy. However, the most I can save under high load is a bit less than 1W. For the number I have, see viewtopic.php?f=28&t=9608&start=130

 

Does it worth? because with SICKBOY 0.2 i have problems with sound delay...or not working sound...

Thanks

 

Another question:

I have applyed all the teaks of powersaving on my rc.local in Ubuntu 8.10, now i have installed SICKBOY Kernel with undervolting support and i have to put on rc.local undervolting config values, should i leave the older powersaving teaks???

Thanks

 

Easy answer. Yes.

Sickboys's kernel has Intel audio powersaving enabled by default. recompile with that option turned off and your problem will be fixed.

 

My AA1 freezes from the moment I do that. It seems I need different values to keep my AA1 running nicely. Most probably I'll try to find them within the next few days...

 

WOuld there be any reason to do this on a 6 cell battery? Would it save even a negligible amount of time?

 

My AA1 runs much cooler with phc enabled.

 

Can someone tell that are right values ???

 

I believe they are some variations across Atoms. Try cat'ing the phc_default_controls file and see what it says.

In my case, I get "12:30 10:25 8:20 6:15"

I changed this to "12:25 10:20 8:15 6:15" and all works fine

The second number is the voltage (in some form). Try just reducing them somewhat. at first.

You can not go below the lowest value (15 in my case).

 

Since i have enable undervolting sometimes when my AAO wake up from suspend my keyboard is not working...
Cant it be undervolting problem???
What about that values on this site ???

http://www.ubuntuaone.com/content/slckb ... eundervolt

Thanks

 

bump

 

The values for undevolting are specific to your particular CPU. Someone else's values will not work. Get your own.

Follow the guide from ubuntu forums here: http://ubuntuforums.org/showthread.php? ... =undervolt

Cheers,
Mitch

 

Ok I read the tutorial but the test may cause damage to partitions mounted, as have my HOME partition an SDHC afraid that might be corrupt, it is safe to do the test?

 

68 degrees!? I'm using a stock AAO A150 with Ubuntu 8.10, and the temperature has never gone beyond 45 degrees. Now it's been running for about 12 hours, and the temperature is 40 degrees. I don't use fancontrol and stuff.

 

That is because you are not running at 1.6 GHz with 100% processor used. I maxed out the cpu for these tests using burnMMX, as I stated in my original post.