sched/idle: Merge kernel/sched/idle.c and kernel/sched/idle_task.c

Merge these two small .c modules as they implement two aspects
of idle task handling.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/Makefile

@@ -17,8 +17,9 @@ CFLAGS_core.o := $(PROFILING) -fno-omit-frame-pointer
 endif
 
 obj-y += core.o loadavg.o clock.o cputime.o
-obj-y += idle_task.o fair.o rt.o deadline.o
-obj-y += wait.o wait_bit.o swait.o completion.o idle.o
+obj-y += idle.o fair.o rt.o deadline.o
+obj-y += wait.o wait_bit.o swait.o completion.o
+
 obj-$(CONFIG_SMP) += cpupri.o cpudeadline.o topology.o stop_task.o
 obj-$(CONFIG_SCHED_AUTOGROUP) += autogroup.o
 obj-$(CONFIG_SCHEDSTATS) += stats.o

kernel/sched/idle.c

@@ -1,5 +1,9 @@
 /*
- * Generic entry points for the idle threads
+ * Generic entry points for the idle threads and
+ * implementation of the idle task scheduling class.
+ *
+ * (NOTE: these are not related to SCHED_IDLE batch scheduled
+ *        tasks which are handled in sched/fair.c )
  */
 #include "sched.h"
 
@@ -33,13 +37,15 @@ void cpu_idle_poll_ctrl(bool enable)
 static int __init cpu_idle_poll_setup(char *__unused)
 {
 	cpu_idle_force_poll = 1;
+
 	return 1;
 }
 __setup("nohlt", cpu_idle_poll_setup);
 
 static int __init cpu_idle_nopoll_setup(char *__unused)
 {
 	cpu_idle_force_poll = 0;
+
 	return 1;
 }
 __setup("hlt", cpu_idle_nopoll_setup);
@@ -51,12 +57,14 @@ static noinline int __cpuidle cpu_idle_poll(void)
 	trace_cpu_idle_rcuidle(0, smp_processor_id());
 	local_irq_enable();
 	stop_critical_timings();
+
 	while (!tif_need_resched() &&
 		(cpu_idle_force_poll || tick_check_broadcast_expired()))
 		cpu_relax();
 	start_critical_timings();
 	trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 	rcu_idle_exit();
+
 	return 1;
 }
 
@@ -337,3 +345,116 @@ void cpu_startup_entry(enum cpuhp_state state)
 	while (1)
 		do_idle();
 }
+
+/*
+ * idle-task scheduling class.
+ */
+
+#ifdef CONFIG_SMP
+static int
+select_task_rq_idle(struct task_struct *p, int cpu, int sd_flag, int flags)
+{
+	return task_cpu(p); /* IDLE tasks as never migrated */
+}
+#endif
+
+/*
+ * Idle tasks are unconditionally rescheduled:
+ */
+static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int flags)
+{
+	resched_curr(rq);
+}
+
+static struct task_struct *
+pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
+{
+	put_prev_task(rq, prev);
+	update_idle_core(rq);
+	schedstat_inc(rq->sched_goidle);
+
+	return rq->idle;
+}
+
+/*
+ * It is not legal to sleep in the idle task - print a warning
+ * message if some code attempts to do it:
+ */
+static void
+dequeue_task_idle(struct rq *rq, struct task_struct *p, int flags)
+{
+	raw_spin_unlock_irq(&rq->lock);
+	printk(KERN_ERR "bad: scheduling from the idle thread!\n");
+	dump_stack();
+	raw_spin_lock_irq(&rq->lock);
+}
+
+static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
+{
+}
+
+/*
+ * scheduler tick hitting a task of our scheduling class.
+ *
+ * NOTE: This function can be called remotely by the tick offload that
+ * goes along full dynticks. Therefore no local assumption can be made
+ * and everything must be accessed through the @rq and @curr passed in
+ * parameters.
+ */
+static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
+{
+}
+
+static void set_curr_task_idle(struct rq *rq)
+{
+}
+
+static void switched_to_idle(struct rq *rq, struct task_struct *p)
+{
+	BUG();
+}
+
+static void
+prio_changed_idle(struct rq *rq, struct task_struct *p, int oldprio)
+{
+	BUG();
+}
+
+static unsigned int get_rr_interval_idle(struct rq *rq, struct task_struct *task)
+{
+	return 0;
+}
+
+static void update_curr_idle(struct rq *rq)
+{
+}
+
+/*
+ * Simple, special scheduling class for the per-CPU idle tasks:
+ */
+const struct sched_class idle_sched_class = {
+	/* .next is NULL */
+	/* no enqueue/yield_task for idle tasks */
+
+	/* dequeue is not valid, we print a debug message there: */
+	.dequeue_task		= dequeue_task_idle,
+
+	.check_preempt_curr	= check_preempt_curr_idle,
+
+	.pick_next_task		= pick_next_task_idle,
+	.put_prev_task		= put_prev_task_idle,
+
+#ifdef CONFIG_SMP
+	.select_task_rq		= select_task_rq_idle,
+	.set_cpus_allowed	= set_cpus_allowed_common,
+#endif
+
+	.set_curr_task          = set_curr_task_idle,
+	.task_tick		= task_tick_idle,
+
+	.get_rr_interval	= get_rr_interval_idle,
+
+	.prio_changed		= prio_changed_idle,
+	.switched_to		= switched_to_idle,
+	.update_curr		= update_curr_idle,
+};