Why do we need a swapper task in linux?

Question

The idle task (a.k.a. swapper task) is chosen to run when no more runnable tasks in the run queue at the point of task scheduling. But what is the usage for this so special

Answer 1

There is actually one idle task per cpu, but it's not held in the main task list, instead it's in the cpu's "struct rq" runqueue struct, as a struct task_struct * .

This gets activated by the scheduler whenever there is nothing better to do (on that CPU) and executes some architecture-specific code to idle the cpu in a low power state.