sched: Extract the task putting code from pick_next_task()

Introduce a new function put_prev_task_balance() to do the balance
when necessary, and then put previous task back to the run queue.
This function is extracted from pick_next_task() to prepare for
future usage by other type of task picking logic.

No functional change.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/5a99860cf66293db58a397d6248bcb2eee326776.1587464698.git.yu.c.chen@intel.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9a2fbf98fd6fa2ea3c420d02ac4cb20d2ba73958..2e6ba9e301f031d0941eede35e0a658dc4ccd393 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3899,6 +3899,28 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
        schedstat_inc(this_rq()->sched_count);
 }
 
+static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
+                                 struct rq_flags *rf)
+{
+#ifdef CONFIG_SMP
+       const struct sched_class *class;
+       /*
+        * We must do the balancing pass before put_prev_task(), such
+        * that when we release the rq->lock the task is in the same
+        * state as before we took rq->lock.
+        *
+        * We can terminate the balance pass as soon as we know there is
+        * a runnable task of @class priority or higher.
+        */
+       for_class_range(class, prev->sched_class, &idle_sched_class) {
+               if (class->balance(rq, prev, rf))
+                       break;
+       }
+#endif
+
+       put_prev_task(rq, prev);
+}
+
 /*
  * Pick up the highest-prio task:
  */
@@ -3932,22 +3954,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
        }
 
 restart:
-#ifdef CONFIG_SMP
-       /*
-        * We must do the balancing pass before put_next_task(), such
-        * that when we release the rq->lock the task is in the same
-        * state as before we took rq->lock.
-        *
-        * We can terminate the balance pass as soon as we know there is
-        * a runnable task of @class priority or higher.
-        */
-       for_class_range(class, prev->sched_class, &idle_sched_class) {
-               if (class->balance(rq, prev, rf))
-                       break;
-       }
-#endif
-
-       put_prev_task(rq, prev);
+       put_prev_task_balance(rq, prev, rf);
 
        for_each_class(class) {
                p = class->pick_next_task(rq);