HowTo: Undervolt your notebook CPU for longer battery life

[Ares Drake]

I have some questions:
¿can I change the VIDS to 24 0 0 0?¿or it will be the same as 24 1 1 1?
¿why are the cpu wasting so much energy when they can run at lower voltage with the same results?if this is safe it would be better, ¿is it safe?

1. I think 0 doesn't work, so 24 1 1 1 is the lowest. Wouldn't make much difference anyway.

2. Making CPUs is a little bit like growing tomatoes. Not all fruits are equal. Likewise, all cpus even of the same kind differ a little bit. So the lowest safe voltage is an individual value for each single cpu. For the cpu manufacturer (intel) it would be too expensive to test them all for their lowest save voltage. So they specify a limit and just test if they work at that limit. As the lowest safe voltage for a given cpu is lower than the specified limit, the difference is wasted.

3. If it is not save (i.e. you set the voltage too low) your computer will freeze / lock up. But as you discribed above you checked for that, so you can assume it is safe.

[guilleml]

1. I think 0 doesn't work, so 24 1 1 1 is the lowest. Wouldn't make much difference anyway.

2. Making CPUs is a little bit like growing tomatoes. Not all fruits are equal. Likewise, all cpus even of the same kind differ a little bit. So the lowest safe voltage is an individual value for each single cpu. For the cpu manufacturer (intel) it would be too expensive to test them all for their lowest save voltage. So they specify a limit and just test if they work at that limit. As the lowest safe voltage for a given cpu is lower than the specified limit, the difference is wasted.

3. If it is not save (i.e. you set the voltage too low) your computer will freeze / lock up. But as you discribed above you checked for that, so you can assume it is safe.

Thanks for your answers
The system seems pretty stable now, it's even safe! I'm quite happy with this tune.

[shador]

Just one question before I get this started. If I by some reason want all of this undone, how do I do that?

[knix]

Anybody got a 2.6.27-2 64-bit module? I'm running Intrepid 64 bit on a C2D and Pressureman's module didn't work.

Thanks.

edit: or 2.6.27-3?
Or a patch for either?

[cheaptrick]

i'm using a C2D LV7500 1.6ghz

cat /sys/devices/system/cpu/cpu0/cpufreq/phc_controls gives me
9:37 8:27 6:21 136:11


The first test stoped at
Default VIDs: 37 27 21 11
Current VIDs: 2 27 21 11
Testing VID: 2 (732 mV)

it did not stop until i accidentally pressed a key
and i did noticed that the cpu temperature increased by more 10 degrees during the test
ok the 1st test did not crash at all!
the next few tests crashed during the first round

and i got this
Default VIDs: 37 27 21 11
Current VIDs: 4 2 1 1

Before i continue with step 5 ,does this look right? it seems weird for me.

[pressureman]

Module for latest Intrepid kernel, 2.6.27-3-generic (32 bit)

[Tao]

Which PHC patch did you use for interpid kernel?

[pressureman]

Which PHC patch did you use for interpid kernel?

The one contained in this forum thread http://phc.athousandnights.de/viewtopic.php?f=13&t=2

It says it's for 2.6.26, but works fine in 2.6.27. I guess the acpi-cpufreq source hasn't changed between versions (or at least, not significantly enough for the patch to fail to apply cleanly).

[kszonek]

The one contained in this forum thread http://phc.athousandnights.de/viewtopic.php?f=13&t=2

It says it's for 2.6.26, but works fine in 2.6.27. I guess the acpi-cpufreq source hasn't changed between versions (or at least, not significantly enough for the patch to fail to apply cleanly).

I used this patch with 2.6.27-3 64bit kernel, it was my first time with phc. After reboot i have problems with 'podprobe acpi_cpufreq':

FATAL: Error inserting acpi_cpufreq (/lib/modules/2.6.27-3-generic/kernel/arch/x86/kernel/cpu/cpufreq/acpi-cpufreq.ko): Invalid module format

I tried to recompile module, I also used your module from post above (32bit one, there was a chance...), but I cant make it working. I left Microsoft 3 weeks ago, I am fresh with linux and the last thing I miss is long battery time with Vista+RMCLock.

Any idea what is wrong?

edit:
of course with backup version of acpi_cpufreq.ko scalling works OK and "lsmod | grep acpi_cpufreq" shows loaded module, but after replace module is not loaded at startup and it cant be loaded manually. Some HOWTOs says to check for speedstep module, but it is not loaded.

edit2:
I have 2 ubuntu on hdd, because I dont want to damage main one with experiments, but I tried to use acpi_cpufreq with first OS (2.6.24-19 64bit). Precompiled module didn't work, but I made one myself and it seems to be ok. Only seems, because every change of phc_controls does nothing. With dual burnMMX in background temps are about 85oC with 11:43, 11:20 and even 11:1. Same with other multipliers - on Vista temperature drop was huge.

I should add that my laptop is Compal FL90, with T7500 cpu and 8600gt.

Now I am trying to run linux-phc-optimize-script, but I am receiving error about missing file functions.bash (i have download it of course, to the same directory - Desktop). Now I am tired fighting with phc (why it is not as simple as with Microsoft) - I should better go sleep.

[anjie]

Hello,

First, thank very much for the useful howto (hope it will work for me soon).

could anyone tell me why at this step

cat /sys/devices/system/cpu/cpu0/cpufreq/phc_controls

I get

"no device"? I'm sure I've done all the previous steps well.
I've checked that the copied file was in the right place, and it is.
I've rebooted twice, using two different kernels... 18 - 19.


Thanks,
Anjie