All cores do get used, you can see them with top. Core usage will vary by affinity, some processes like OpenVPN are locked to specific cores.
If something has high CPU usage then you need to track it down using top.
Thanks for the pointer @RMerlin.
I see only 1 process with CPU3 on 388.2 in the top output, but more processes assigned to CPU3 on 386.7_2.
What might be the reason of this change?
As for the higher CPU usage, I noticed the process - sysstate is using up a lot of CPU cycles.
I have a USB HDD attached for FTP use, and the high CPU usage goes away if I unmount the disk.
Any idea what might be the cause please?
Thank you.