Observation

My cpu frequency is locked to 400mhz for all cores, even the cpu governor is set to performance policy.
The power profile in x11 is also set to performance.
Before this happens, I just charge my laptop via a bad power supply (which shows not in charging, the power supply is just enough to keep the balance.), and the battery is low.

I try to disable the powersave management in bios, and reboot the laptop, the problems remains the same.

It seems like its a hardware bug about the power adapter, when the ac is plug-in, the hardware will notify the cpu clock and sets its policy to performance policy in hardware-level, and if the ac is plug-out, sets to powersave policy.

The key point is that, after a bad power supply, the hardware detects something wrong, it thinks the power adapter is always off, and writes this data into the hardware storage, so there is nothing to do with the software-level.

Solution

Keep pressing the power button, and reset the bios. (This also resets all the data stored in the hardware-level.)