CPU scheduling and kernel-level threads -

CPU scheduling and kernel-level threads -

my textbook mentions next sentence:

on operating systems back upwards them, kernel-level threads - not processes - beingness scheduled operating system.

i understand cpu scheduling, sentence not create sense. mean scheduler programme allocates cpu kernel-level threads according specific algorithms?

aren't kernel-level processes scheduled? or not exist in operating systems back upwards kernel-level threads?

when referring threads , processes in operating scheme context, process means thread own memory space , thread means thread shares it's memory space other threads.

so process context-switches have higher cost thread context-switches, because there higher over-head when switching process context.

kernel