sched_ext: Simplify UP support by enabling sched_class->balance() in UP

On SMP, SCX performs dispatch from sched_class->balance(). As balance() was
not available in UP, it instead called the internal balance function from
put_prev_task_scx() and pick_next_task_scx() to emulate the effect, which is
rather nasty.

Enabling sched_class->balance() on UP shouldn't cause any meaningful
overhead. Enable balance() on UP and drop the ugly workaround.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: David Vernet <void@manifault.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 957c1a6626d2..010f01f606c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5857,7 +5857,6 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
 static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
 				  struct rq_flags *rf)
 {
-#ifdef CONFIG_SMP
 	const struct sched_class *start_class = prev->sched_class;
 	const struct sched_class *class;
 
@@ -5880,10 +5879,9 @@ static void put_prev_task_balance(struct rq *rq, struct task_struct *prev,
 	 * a runnable task of @class priority or higher.
 	 */
 	for_active_class_range(class, start_class, &idle_sched_class) {
-		if (class->balance(rq, prev, rf))
+		if (class->balance && class->balance(rq, prev, rf))
 			break;
 	}
-#endif
 
 	put_prev_task(rq, prev);