Linux commands takes seconds to finish

Question

I'm on an ARM board running Linux.

root@hobot:~# uname -a
Linux hobot 6.1.94-rt33 #1 SMP PREEMPT_RT Fri Nov  8 15:11:35 CST 2024 aarch64 GNU/Linux

I don't know what happend with my OS today, I just suddenly found out that shell commands takes too long to finish. but everything was fine a little while ago.

like:

As you can see, ls takes about over 5 seconds and it takes 100% CPU in core 4th.

What happened ?

What should I monitor ?

Please help. Thanks a lot.