[RFC PATCH] 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 ake_affine_idle(), we should use the real running-tasks
in rq to check whether we should place the wake-up task to
current cpu.

Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Signed-off-by: Xuewen Yan <xuewen.yan@xxxxxxxxxx>
---
 kernel/sched/fair.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1c0ef435a7aa..2d6d5582c3e9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7342,8 +7342,15 @@ 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);
+		int nr_delayed;
+
+		nr_delayed = rq->cfs.h_nr_queued - rq->cfs.h_nr_runnable;
+
+		if ((rq->nr_running - nr_delayed) == 1)
+			return this_cpu;
+	}
 
 	if (available_idle_cpu(prev_cpu))
 		return prev_cpu;
-- 
2.25.1