CPU keeps getting throttled to oblivion (~400 MHz)

Ask Fedora
1

I have a strange problem, where my CPU gets throttled whenever the utilisation goes a bit high. There’s absolutely no way to get sustained high use. And the throttled speed goes down to as low as 400MHz!

I’m on a ThinkPad T495s

$ inxi -Cm
Memory:    RAM: total: 13.33 GiB used: 6.49 GiB (48.7%)
           Array-1: capacity: 64 GiB slots: 2 EC: None
           Device-1: DIMM 0 size: 8 GiB speed: 2400 MT/s
           Device-2: DIMM 0 size: 8 GiB speed: 2400 MT/s
CPU:       Info: Quad Core model: AMD Ryzen 7 PRO 3700U w/ Radeon Vega Mobile Gfx bits: 64 type: MT MCP cache: L2: 2 MiB
           Speed: 435 MHz min/max: 1400/2300 MHz Core speeds (MHz): 1: 435 2: 436 3: 870 4: 871 5: 435 6: 434 7: 871 8: 871

I looked at the scaling_governor, it’s set to schedutil, which according to the kernel docs is the right thing to do. When I manually set all the governors to performance, I still don’t get any significant improvement (as you can see from the inxi output).

Can someone shed some light here?

2

Maybe it is a cooling problem? Does it throttle when the CPU temperature hits a certain value?

3

It does become a bit hot, but not much. As per conky it never even touches 60, hovers around low 50s.

I have opened up the laptop too, there wasn’t much to be cleaned apart from what you would expect for a year old laptop.

I also looked at the BIOS, I think the options were battery optimised, balanced, and performance. If I remember correctly balanced was selected there. And since I’m mostly plugged in, I would expect balanced and performance to be the same.

In the past (on other ThinkPads I have owned), I have run long multi hour long computations, with CPU temps touching 70-80 at times. Which is why I find this so perplexing, and not really sure how to debug.

4

Is the throttling when on battery, AC, or both?

I had a bizarre issue with the CPU throttling to below the minimum frequency but only when on battery. The solution was to clean the battery contacts. https://discussion.fedoraproject.org/t/laptop-cpu-dropping-to-unusably-slow-frequency-on-battery/68042

But mine has a removable battery while the T495s does not seem to. Still maybe something to consider.

5

I’m rarely on battery. This happens when I’m plugged in. Usually triggered by Zoom/Teams eating CPU (most typical scenario), or say, if I try to transcode a video.

6

When did the issue start? Doesn’t sound normal. Might want to monitor what’s going on with sensors.

7

Can’t be sure, I can only recall these issues starting to annoy me around Nov-Dec. Good idea with sensors, I’ll setup a cron job to log everything.