how do I compile a kernel with acpi_cpufreq as a module?

[necbot]

I would like to add the phc-intel module to my kernel so I can undervolt my processor. I got the phc-intel module compiled into a .deb package successfully and I installed it. However, to load it, I have to unload acpi by typeing "sudo modprobe -r acpi-cpufreq". When I do this it says I can't unload this because it's built in to the kernel. Okay, fine, so this means I have to rebuild the kernel with acpi-cpufreq as a module.

I'm following the instructions here (https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel). I'm at the point where I need to create a config file that specifies that acpi-cpufreq is supposed to be a module. I ran...

chmod a+x debian/scripts/*chmod a+x debian/scripts/misc/*
fakeroot debian/rules clean
fakeroot debian/rules editconfigs

I only edited the i386/config.flavour.generic because I'm using 32 bit. The config editor appears and I go to Power Management and ACPI options -> ACPI (Acvanced Configuration and Power Interface) Support. My question is... Am I in the right place and if I am, which settings do I switch from builtin to module? The processor option seems the likely choice. However, when I change this to module and save the config file I get the following error when the check-config runs...

check-config: /tmp/tmp.SnaxIwOYEp/CONFIGS/i386-config.flavour.generic: loading config
check-config: /home/user/src/ubuntu-raring/debian.master/config/enforce: loading checks
check-config: FAIL: !exists CONFIG_XEN_ACPI_PROCESSOR | value CONFIG_XEN_ACPI_PROCESSOR y
check-config: 46/47 checks passed -- exit 1

So am I changing the wrong setting in the config? Am I on the right track to begin with? Any help would be much appreciated. Thanks.

[tgalati4]

What version of linux are you running?


uname -a

What you do depends on the version. Older versions of the kernel required a recompile with the undervolt hooks, but I believe the newer versions have the hooks already available. The check-config error could be that the XEN (virtual machine hypervisor) is incompatible with undervolting, so that would have to be set to No.

What is the CPU?

[necbot]

uname -a prints "Linux pc 3.8.0-22-generic #33-Ubuntu SMP Thu May 16 15:17:59 UTC 2013 i686 i686 i686 GNU/Linux"

The cpu is an Intel Celeron (Ivy bridge) G1620

[tgalati4]

Some interesting notes about underclocking Ivy Bridge processors: http://www.anandtech.com/show/5763/undervolting-and-overclocking-on-ivy-bridge

Because of the smaller traces in the processor design, you may not benefit as much undervolting as in previous processors. Proceed carefully.

What is the output of:


modinfo phc-intel

Is this a dual-boot system? If so, then run all of Intel's tools first in Windows to determine stability of the processor and motherboard at undervolt, otherwise you will spend several hours of compiling and then spend more hours stability testing. The Windows tools are complete and you can get the same results in linux, but it requires a lot of work.

Don't expect massive payback, though. What are your goals for undervolting?

Couple more links:
http://www.silentpcreview.com/forums/viewtopic.php?f=23&t=64474

http://forums.bit-tech.net/showthread.php?t=223382

What is the output of:


cpufreq-info

It might look something like:

tgalati4@tpad-Gloria7 ~ $ cpufreq-info
cpufrequtils 004: cpufreq-info (C) Dominik Brodowski 2004-2006
Report errors and bugs to cpufreq@lists.linux.org.uk, please.
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which need to switch frequency at the same time: 0
hardware limits: 800 MHz - 2.13 GHz
available frequency steps: 2.13 GHz, 1.87 GHz, 1.60 GHz, 1.33 GHz, 1.07 GHz, 800 MHz
available cpufreq governors: conservative, ondemand, userspace, powersave, performance
current policy: frequency should be within 800 MHz and 2.13 GHz.
The governor "ondemand" may decide which speed to use
within this range.
current CPU frequency is 800 MHz.
cpufreq stats: 2.13 GHz:0.06%, 1.87 GHz:0.00%, 1.60 GHz:0.01%, 1.33 GHz:0.01%, 1.07 GHz:0.01%, 800 MHz:1.36% (68310)

It is not clear why you need to (re)compile acpi_cpufreq as it is part of the current kernel.

[necbot]

Ah, I see, the benefits of undervolting seem to be minor with modern intel cpus. I was under the impression that acpi_cpufreq was built into the ubuntu kernel. However, if acpi_cpufreq were a module then I could unload it and load the phc_intel module instead, which is why I wanted to try this. However, I think I'll pass on undervolting since I'm only doing it to see how low I can get my systems idle power consumption. I may try undervolting on my AMD APU build, so an answer to how to compile the kernel with the phc module would be great.

[tgalati4]

For understanding how PHC works, spend some time here: http://www.linux-phc.org/forum/

The last time I compiled my kernel for PHC and undervolting was a few years ago on Jaunty (9.04), so I presume things have changed. The basic procedure for compiling the kernel has not changed, but what patches to apply and what modules need modification have changed, so you will have to keep researching.

Here's a how-to for 12.04: http://linuxsolver.blogspot.com/2012/05/undervolting-cpu-in-ubuntu-1204.html