swapper程序，即idle程序，其主體是cpu_idle_loop

/*
 * Generic idle loop implementation
 *
 * Called with polling cleared.
 */
static void cpu_idle_loop(void)
{
int cpu = smp_processor_id();


       while (1) {
/*
 * If the arch has a polling bit, we maintain an invariant:
 *
 * Our polling bit is clear if we're not scheduled (i.e. if
 * rq->curr != rq->idle).  This means that, if rq->idle has
 * the polling bit set, then setting need_resched is
 * guaranteed to cause the cpu to reschedule.
 */


__current_set_polling();
quiet_vmstat();
tick_nohz_idle_enter();


while (!need_resched()) {
 

check_pgt_cache();
rmb();


if (cpu_is_offline(cpu)) {
cpuhp_report_idle_dead();
arch_cpu_idle_dead();
}


local_irq_disable();
arch_cpu_idle_enter();


/*
 * In poll mode we reenable interrupts and spin.
 *
 * Also if we detected in the wakeup from idle
 * path that the tick broadcast device expired
 * for us, we don't want to go deep idle as we
 * know that the IPI is going to arrive right
 * away
 */下面這個是呼叫體系相關的睡眠程式碼
if (cpu_idle_force_poll || tick_check_broadcast_expired())
cpu_idle_poll();
else
cpuidle_idle_call();
 



arch_cpu_idle_exit();
}


/*
 * Since we fell out of the loop above, we know
 * TIF_NEED_RESCHED must be set, propagate it into
 * PREEMPT_NEED_RESCHED.
 *
 * This is required because for polling idle loops we will
 * not have had an IPI to fold the state for us.
 */
preempt_set_need_resched();
tick_nohz_idle_exit();
__current_clr_polling();


/*
 * We promise to call sched_ttwu_pending and reschedule
 * if need_resched is set while polling is set.  That
 * means that clearing polling needs to be visible
 * before doing these things.
 */
smp_mb__after_atomic();


sched_ttwu_pending();
schedule_preempt_disabled();
}
 

}

開機後，通過下面方式進入idle：

start_kernel --> rest_init --> cpu_startup_entry
void cpu_startup_entry(enum cpuhp_state state)
{
/*
 * This #ifdef needs to die, but it's too late in the cycle to
 * make this generic (arm and sh have never invoked the canary
 * init for the non boot cpus!). Will be fixed in 3.11
 */
#ifdef CONFIG_X86
/*
 * If we're the non-boot CPU, nothing set the stack canary up
 * for us. The boot CPU already has it initialized but no harm
 * in doing it again. This is a good place for updating it, as
 * we wont ever return from this function (so the invalid
 * canaries already on the stack wont ever trigger).
 */
boot_init_stack_canary();
#endif
arch_cpu_idle_prepare();
cpuhp_online_idle(state);
cpu_idle_loop();
}