How to limit the cpu usage of Mathematica?

I am runing mathematica with ParallelMap[], on a win10 computer with 8 physical cores.

The cpu usage always rocks up to 100%, though LaunchKernels[4] is applied in the first place. It remains 100%, even though I only use Map[] without Parallel.

I have tried to configurethe parallel preferences, but nothing changes.

Could somebody help me out?

When use Map[] without parallel running,

Map[]

When use ParallelMap[] following LaunchKernels[4]

ParallelMap[] following LaunchKernels[4]