Irq/9-acpi process sucking up half of my CPU

Hi everybody,
I am experiencing a weird behavior on my laptop.
I have this irq/9-acpi process constantly using about 70% of one CPU and kworker/0:2-kacpi_notify using another 20% of one CPU.

Here is an excerpt from “top”:

Tasks: 295 total, 2 running, 292 sleep, 1 d-sleep, 0 stopped, 0 zombie
%Cpu(s):  8,5 us, 26,2 sy,  2,1 ni, 46,9 id, 16,0 wa,  0,0 hi,  0,3 si,  0,0 st 
MiB Mem : 15870,98+total,  396,477 free, 6388,324 used, 10405,18+buff/cache     
MiB Swap: 15863,99+total, 15861,74+free,    2,250 used. 9482,660 avail Mem 

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND                                                                                      
     57 root     -51   0       0      0      0 R 70,44 0,000  15:39.66 irq/9-acpi                                                                                   
     60 root      20   0       0      0      0 I 20,93 0,000   2:07.88 kworker/0:2-kacpi_notify

Laptop is an HP Elitebook which has always worked well.
After a bit of tweaking, I understood the reason ot this weird behavior: I was using an external monitor connected via USB-C to the laptop.
As soon as I disconnect the external monitor, CPU usage is back to normal.
I normally use HDMI, so I never noticed this behavior.
Have you ever noticed this behavior?
How can I fix the high CPU usage?

Thank you in advance
Cris

No magic USB usage is more CPU intense then output direct via GPU. There are always trade offs :dizzy_face:

Thank you @gogalthorp !
However I am a bit perplexed: when I’m using a single external monitor I use HDMI, as stated earlier. However, when I’m at a client’s office I often use a USB-C hub which connects power, sound, two external monitors and mouse/keyboard. With this setup, I never noticed an increased CPU consumption.

That error may indicate a problem with your system’s ACPI (Advanced Configuration and Power Interface) interrupt handler, specifically related to IRQ (Interrupt Request) line 9.

Use lspci and check /proc/interrupts output for IRQ assignment clues.

Did you check for error messages related to ACPI or IRQ 9 in the system logs?

Check for driver updates for the device connected to IRQ 9.

Check the system’s power management settings (that they are proper)

Check for a possible BIOS update

Consider checking for faulty hardware components associated with the problematic IRQ.

Thank you @myswtest , I will check and come back to you ASAP.