sched: cfs core, kernel/sched_idletask.c

add kernel/sched_idletask.c - which implements the idle thread
scheduling class. This further simplifies sched.c (under CFS),
for example a number of 'if (p == rq->idle)' type of special-cases
can be removed from sched.c, and schedule() gets simpler too.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 71 insertions, 0 deletions

diff --git a/kernel/sched_idletask.c b/kernel/sched_idletask.c
new file mode 100644
index 000000000000..41841e741c4a
--- /dev/null
+++ b/kernel/sched_idletask.c
@@ -0,0 +1,71 @@
+/*
+ * idle-task scheduling class.
+ *
+ * (NOTE: these are not related to SCHED_IDLE tasks which are
+ *  handled in sched_fair.c)
+ */
+
+/*
+ * Idle tasks are unconditionally rescheduled:
+ */
+static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p)
+{
+        resched_task(rq->idle);
+}
+
+static struct task_struct *pick_next_task_idle(struct rq *rq, u64 now)
+{
+        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 sleep, u64 now)
+{
+        spin_unlock_irq(&rq->lock);
+        printk(KERN_ERR "bad: scheduling from the idle thread!\n");
+        dump_stack();
+        spin_lock_irq(&rq->lock);
+}
+
+static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, u64 now)
+{
+}
+
+static int
+load_balance_idle(struct rq *this_rq, int this_cpu, struct rq *busiest,
+                        unsigned long max_nr_move, unsigned long max_load_move,
+                        struct sched_domain *sd, enum cpu_idle_type idle,
+                        int *all_pinned, unsigned long *total_load_moved)
+{
+        return 0;
+}
+
+static void task_tick_idle(struct rq *rq, struct task_struct *curr)
+{
+}
+
+/*
+ * Simple, special scheduling class for the per-CPU idle tasks:
+ */
+static struct sched_class idle_sched_class __read_mostly = {
+        /* 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,
+
+        .load_balance           = load_balance_idle,
+
+        .task_tick              = task_tick_idle,
+        /* no .task_new for idle tasks */
+};