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I have an old spare Dell V131 that I use sometimes and after a while of being on, it caps CPU frequency to its lowest (800 Mhz) and stays there.

The variable

# cat /proc/cpuinfo | grep -i "cpu Mhz"
cpu MHz     : 1281.633
cpu MHz     : 1324.313
cpu MHz     : 1103.786
cpu MHz     : 1444.849

goes to solid

cpu MHz     : 798.181
cpu MHz     : 798.179
cpu MHz     : 798.182
cpu MHz     : 798.178

and then never increases again until I reboot it. That, obviously, makes it painfully slow.

I tried different power supplies. It also happens on battery, so it's more likely a heat issue, not a power draw problem. However, it's clearly not really overheating since a reboot helps and it's not spinning up the fans or increasing the frequency after being idle for a while.

How can I find out what is lowering the frequency and, preferably, disable it or at least, reset its state from time to time without rebooting? Unless the laptop physically catches fire, I don't care about potential damage to it.

It's an Ubuntu 20.04.3 with a 5.4.0-91-generic kernel.

EDIT: Here's the suggested sensors output.

# sensors
coretemp-isa-0000
Adapter: ISA adapter
Package id 0:  +48.0°C  (high = +86.0°C, crit = +100.0°C)
Core 0:        +48.0°C  (high = +86.0°C, crit = +100.0°C)
Core 1:        +48.0°C  (high = +86.0°C, crit = +100.0°C)

BAT0-acpi-0
Adapter: ACPI interface
in0:          11.44 V

curr1:         2.56 A


dell_smm-virtual-0
Adapter: Virtual device
Processor Fan:    0 RPM
Processor Fan:    0 RPM
CPU:            +47.0°C

Other:          +47.0°C

Other:          +51.0°C

GPU:            +16.0°C

Other:          +63.0°C


acpitz-acpi-0
Adapter: ACPI interface
temp1:        +47.5°C  (crit = +99.0°C)
Damn Terminal
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    You really don't know if it overheats or not. I would use lm-sensors to check the temps, and also check the BIOS for power management features. – mikewhatever Jan 03 '22 at 22:17
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    What is your processor make and model? Is it an Intel i5-2410M? – Doug Smythies Jan 03 '22 at 22:23
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    Have you tried to clean the CPU fan physically ? you know... dissamble and wipe out thermal paste and apply some new ?? – Matthias Lenmher Jan 03 '22 at 22:54
  • @mikewhatever Will do. However, if it was really overheating, reboot wouldn't help since booting is pretty CPU intensive. – Damn Terminal Jan 03 '22 at 23:26
  • @DougSmythies It's 2430, according to procinfo the exact model name: Intel(R) Core(TM) i5-2430M CPU @ 2.40GHz – Damn Terminal Jan 03 '22 at 23:27
  • @MatthiasLenmher I have cleaned the fan (vacuumed) but didn't wipe out the thermal paste and apply new. I'm not very handy and this laptop is pretty hard to disassemble. Would that be your first recommendation? – Damn Terminal Jan 03 '22 at 23:28
  • First of all, if you dont take care about dust-dirt cleaning, u can begin from that... search some tutorials from internet for how clean your specific model (i recommend youtube). if you dont have idea about hartdware please contact for specialized help – Matthias Lenmher Jan 04 '22 at 00:00
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    It doesn't solve the problem of discovering what is throttling the CPU but it does allow you to un-throttle it without rebooting: GUI or simple Bash script to throttle the CPU?. The answer is posted here in Ask Ubuntu and the bash scxript is called cpuf (short for CPU Frequency). – WinEunuuchs2Unix Jan 04 '22 at 00:24
  • @WinEunuuchs2Unix Doesn't seem to have any effect. I've installed it, set the minimum frequency to 1200 but it's still at 798. – Damn Terminal Jan 04 '22 at 00:39
  • as i said, i suggest you make a thermal paste wipeout =), a little bit of isopropylic alcohol, and put some new =) ! – Matthias Lenmher Jan 04 '22 at 03:57

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