[RFC PATCH V2 1/3] sched/fair: Fixup-wake_up_sync-vs-DELAYED_DEQUEUE

[Xuewen Yan]

Delayed dequeued feature keeps a sleeping task enqueued until its
lag has elapsed. As a result, it stays also visible in rq->nr_running.
So when in wake_affine_idle(), we should use the real running-tasks
in rq to check whether we should place the wake-up task to
current cpu.
On the other hand, add a helper function to return the nr-delayed.

Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
V2:
- add helper function (Vincent)
---
 kernel/sched/fair.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1c0ef435a7aa..a354f29c4f6f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7181,6 +7181,11 @@ static bool dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	return true;
 }
 
+static inline unsigned int cfs_h_nr_delayed(struct rq *rq)
+{
+	return (rq->cfs.h_nr_queued - rq->cfs.h_nr_runnable);
+}
+
 #ifdef CONFIG_SMP
 
 /* Working cpumask for: sched_balance_rq(), sched_balance_newidle(). */
@@ -7342,8 +7347,12 @@ wake_affine_idle(int this_cpu, int prev_cpu, int sync)
 	if (available_idle_cpu(this_cpu) && cpus_share_cache(this_cpu, prev_cpu))
 		return available_idle_cpu(prev_cpu) ? prev_cpu : this_cpu;
 
-	if (sync && cpu_rq(this_cpu)->nr_running == 1)
-		return this_cpu;
+	if (sync) {
+		struct rq *rq = cpu_rq(this_cpu);
+
+		if ((rq->nr_running - cfs_h_nr_delayed(rq)) == 1)
+			return this_cpu;
+	}
 
 	if (available_idle_cpu(prev_cpu))
 		return prev_cpu;
-- 
2.25.1