There's more specific answers here, but in general the answer to this question is "only partly". The kernel is what initially gives your process a time slice on

There's more specific answers here, but in general the answer to this question is "only partly". The kernel is what initially gives your process a time slice on the CPU, by setting an alarm for the CPU to return control to the kernel at the end of the time slice, and then just jumping into your code. During your time slice, you can do anything you want to the CPU, and in general only interrupts (timer interrupts, hardware interrupts, page faults, etc) will cause the kernel to get involved again. There are some specific features that CPU designers add to give extra control to the kernel, but that's a feature of the CPU and it's only when the CPU has explicitly added that type of control.