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Here I got a strange problem with my ThinkPad X200.

This notebook uses Intel(R) Core(TM)2 Duo CPU P8600, which has a designed frequency of 2.4GHz. When I use battery only, the maximum scaling frequency can be 2.4GHz, HOWEVER, when I insert the AC adapter, the frequency is limited to 1.6GHz.

The problem still exists even I have disabled cpufreqd, and forced the governor to performance.

That's so weird! Would anybody have an idea?

P.S. My kernel version is 4.19.5.

Akura Ryu
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3 Answers3

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Yeah, no one cares my problem, that's a tremendous pity.

However, luckily, I lave found a solution to deal with it!

What limits the CPU's maximum frequency? BIOS!

The file /sys/devices/system/cpu/cpu*/cpufreq/bios_limit tells the limitation value of BIOS.

On condition that performance governor is activated, when I use battery only, the value of bios_limit is 2400000, the maximum of the hardware. However, when I connect AC adapter, this value will soon lower to 1600000.

By default, Linux's governor follows bios_limit, so the problem occurs. But we can let Linux to ignore it, and don't let the maximum frequency stucks. Just set ignore_ppc to 1.

echo 1 | sudo tee /sys/module/processor/parameters/ignore_ppc

And modify /etc/default/grub to automatically set ignore_ppc on reboot. Open it with root privilege, attach processor.ignore_ppc=1 to GRUB_CMDLINE_LINUX_DEFAULT, just like this:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash processor.ignore_ppc=1"

then run:

sudo update-grub

and reboot.

References:

Akura Ryu
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    didn't work for me :( I've found a file called ``ignore_tpc`` and I don't have any ``bios_limit`` file ! Is it normal ? – Sami Sep 09 '20 at 10:26
  • Didn't work for me on Ubuntu 18.04, Dell Precision M5520. And I also have no file `/sys/devices/system/cpu/cpu0/cpufreq/bios_limit` – Garrett Jul 06 '21 at 21:58
  • [Here](https://askubuntu.com/a/1350470/173693)'s what did work on my machine. – Garrett Jul 07 '21 at 06:36
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It seems to be an option in BIOS. according to this image: BIOS of ThinkPad X200

I hope i help you. Best regards.

Santi
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TLP would come handy in such situations

sudo apt-get install tlp

And check the config file /etc/tlp.conf or tlpui graphical interface

which might give you a clearer idea on your cpu performance limits under AC/BAT

#CPU_SCALING_MAX_FREQ_ON_AC 
#CPU_MAX_PERF_ON_AC
#CPU_SCALING_GOVERNOR_ON_AC
#CPU_BOOST_ON_AC
...
muru
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Rz_CHIFFRE
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