HowTo: Undervolt your notebook CPU for longer battery life

[excogitation]

From my experience undervolting lowers your temperature by a few (~3-8 °C) degrees depending on the the CPU load, ...

I think you're unreasonable expecting figures as high as 15 °C.

Most the time it's only a matter of a few degrees to get those laptop fans to stop and that's what my main interest was when I started using NHC (windows) a few years back.

Unfortunately in Ubuntu my fan still runs about 85% of the time but at least it isn't running 100% and maybe it'll change to the better in the future (... it definitely will with the next laptop ...)

Also undervolting NEVER had any effect on my harddrive temperature (and I've undervolted numerous laptops and even my fileserver running on a Dothan mATX-board).

[eldragon]

doing a dmesg i get the following concerning acpi_cpufreq:
acpi_cpufreq: no version for "struct_module" found: kernel tainted.

does anyone know what that means?

[mrpeaches]

Ok, let me start off by saying that I'm a total Linux newbie. This is my first Ubuntu install and I'm a big fan for the most part. However, I'm interested in undervolting because my CPU fan is always blowing and my laptop does run hotter under ubuntu as compared to XP (I'm dual booting).

So, I looked at the guide and managed to compile and install the PHC thing. I ran the script as well as burnMMX concurrently, but the script counted all the way down to 0 and then crashed. So, going on the advice of others in this thread, I set the values all to 19 and put them in the rc.local file. Unfortunately, this caused my Ubuntu to hang. It loads at boot, then just when it normally goes to the login screen, it just stops with a black screen and is unresponsive. when i went to the recovery boot, and edited out the "echo" commands, ubuntu boots as normal, which is to say, overly warm with the fan always blowing.

Here is some extra information in case it helps:
Ubuntu 8.04 64-Bit
Lenovo X61 laptop
Core2Duo T8300 2.4 Ghz
4GB RAM

and here is what I put into my rc.local file (I upped the 19 to 21 to try and boot with it again, no luck):
echo "13:21 12:21 10:21 8:21 6:21 136:21" > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls
echo "13:21 12:21 10:21 8:21 6:21 136:21" > /sys/devices/system/cpu/cpu1/cpufreq/phc_controls

So, anyone have any ideas? I am totally at a loss as to what to do next. Thank you all for being so kind and helpful so far, and any help anyone could give me would be appreciated!

[aashay]

Ok, let me start off by saying that I'm a total Linux newbie. This is my first Ubuntu install and I'm a big fan for the most part. However, I'm interested in undervolting because my CPU fan is always blowing and my laptop does run hotter under ubuntu as compared to XP (I'm dual booting).

So, I looked at the guide and managed to compile and install the PHC thing. I ran the script as well as burnMMX concurrently, but the script counted all the way down to 0 and then crashed. So, going on the advice of others in this thread, I set the values all to 19 and put them in the rc.local file. Unfortunately, this caused my Ubuntu to hang. It loads at boot, then just when it normally goes to the login screen, it just stops with a black screen and is unresponsive. when i went to the recovery boot, and edited out the "echo" commands, ubuntu boots as normal, which is to say, overly warm with the fan always blowing.

Here is some extra information in case it helps:
Ubuntu 8.04 64-Bit
Lenovo X61 laptop
Core2Duo T8300 2.4 Ghz
4GB RAM

and here is what I put into my rc.local file (I upped the 19 to 21 to try and boot with it again, no luck):
echo "13:21 12:21 10:21 8:21 6:21 136:21" > /sys/devices/system/cpu/cpu0/cpufreq/phc_controls
echo "13:21 12:21 10:21 8:21 6:21 136:21" > /sys/devices/system/cpu/cpu1/cpufreq/phc_controls

So, anyone have any ideas? I am totally at a loss as to what to do next. Thank you all for being so kind and helpful so far, and any help anyone could give me would be appreciated!

Please refer to http://ubuntuforums.org/showpost.php...0&postcount=91 to see how I got the 19 value for MY system. Find the correct value for your system in a similar way.

[HellBoyz77]

From my experience undervolting lowers your temperature by a few (~3-8 °C) degrees depending on the the CPU load, ...

I think you're unreasonable expecting figures as high as 15 °C.

I think that it depends on cpu. For example, with my T5500 i get impressive result. Before the undervolting, when playing Civ4 with Wine, my cpu go always 97-99 degree. Now i get an impressive 75-85 ... This is very reasonable result.

Most the time it's only a matter of a few degrees to get those laptop fans to stop and that's what my main interest was when I started using NHC (windows) a few years back.

Unfortunately in Ubuntu my fan still runs about 85% of the time but at least it isn't running 100% and maybe it'll change to the better in the future (... it definitely will with the next laptop ...)

If you want to manage the fan noise, you probably need to recompile your DSDT table, when i do it the fan lower the noise a lot. I don't remember the link, but i found a guide in this forum on how to do that.

[tesna]

Do anyone know how to patch cpufreq in 26.25.9 kernel? Currently in svn only got patch for 26.24

[Tao]

yes (I've test it on 2.6.25.8 vanilla), with the Teknohog PHC patch. http://howflow.com/tricks/undervolt_..._kernel_2_6_25

But I didn't succeed on the intrepid kernel... (2.6.26rc6 with ubuntu patches)

[chuck232]

Core 2 Duos should have a min voltage of 15. The minimum for Core 2's is 0.9V, so 712mV + 15*12.5mV. This is a documented lowest voltage.

As for the 136: xx number people are seeing, this is a setting available for many of the 800MHz FSB Core 2 Duo's. Typically the lowest multiplier is 6, and for a 800MHz quad-pumped FSB CPU, that equates to 6*200MHz = 1.2GHz. However these 800MHz Core 2 Duos can also drop the FSB. At its lowest operating power state, it downclocks to 8 multiplier * 100MHz FSB (400MHz quad-pumped), or 800MHz. That's why it's listed as the last entry. The 136 number is just the represenation of that power state. I'd go out on a limb and say that every 800MHz FSB Core 2 Duo should be able to do that state at 136:15 (or 0.9V i.e. the lowest operating voltage).

[tesna]

yes (I've test it on 2.6.25.8 vanilla), with the Teknohog PHC patch. http://howflow.com/tricks/undervolt_..._kernel_2_6_25

But I didn't succeed on the intrepid kernel... (2.6.26rc6 with ubuntu patches)

that works great on 2.6.25.9, Thanks!

[M4rotku]

Ok guys,

I've tried to do this several times now and I think I officially qualify as the least competent person ever to view this thread because it seems that everyone else is able to do this.

Would anyone be willing to work with me through private messages or AOL IM or Skype to give me step by step instructions.

It keeps going wrong and I think I know why, but I have no clue what to do about it and I am just really confused at this point. I would've given up by now but my computer really needs to be undervolted.

Much thanks in advance,
M4rotku