Your hunch was correct. I plugged in USB devices in all USB ports and the issue went away. Then I started to unplug them one by one and I noticed that the problem is related only to one of the 3 external USB ports. As soon as I unplug the device from that USB port kworker and ksoftirqd will instantly start to abuse the CPU.
USB devices: $ lsusb Bus 004 Device 006: ID 0cf3:e005 Atheros Communications, Inc. Bus 004 Device 002: ID 0438:7900 Advanced Micro Devices, Inc. Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 003 Device 004: ID 06cb:75bf Synaptics, Inc. Bus 003 Device 003: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller Bus 003 Device 002: ID 0438:7900 Advanced Micro Devices, Inc. Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub Bus 001 Device 002: ID 0bda:5684 Realtek Semiconductor Corp. Bus 001 Device 008: ID 0458:003a KYE Systems Corp. (Mouse Systems) NetScroll+ Mini Traveler / Genius NetScroll 120 <== I connected a mouse to the USB port that I mentioned earlier Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1488426 Title: High CPU usage of kworker/ksoftirqd Status in HWE Next: New Status in linux package in Ubuntu: In Progress Bug description: kworker consuming 71.5% cpu resource ksoftirqd consuming 28.9% cpu resource It leads to power consumption issue and sometimes leads to BT does not work. To manage notifications about this bug go to: https://bugs.launchpad.net/hwe-next/+bug/1488426/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp