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.
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:
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
...
It seems to be an option in BIOS. according to this image: BIOS of ThinkPad X200
I hope i help you. Best regards.
