Intel i5-7200U Kaby Lake. Ubuntu 16.04 LTS.
2 of my 4 processing cores are 100% loaded, even if no processes are running. The load can pass on other cores, but there is always two 100% loaded cores. The issue occurred recently. There is no such issue on Windows 10 on the exact same PC (see screenshots). Maybe there was some update (e.g. to fix Meltdown or Spectre), which loads my CPU.