[PATCH] sched: Precise load checking in get_rr_interval_fair

[Charles Wang <muming.wq@gmail.com>]

From: Charles Wang <muming.wq@taobao.com>

Positive load weight of rq.cfs can not represent positive load weight
of se->cfs_rq. And when se->cfs_rq's load is 0, the slice calculated 
by sched_slice is not that sensible.

Use se->cfs_rq for load checking instead of rq->cfs. And correct the
comments.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Zhu Yanhai <gaoyang.zyh@taobao.com>
Signed-off-by: Charles Wang <muming.wq@taobao.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 539760e..5d58ac9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6086,14 +6086,15 @@ void unregister_fair_sched_group(struct task_group *tg, int cpu) { }
 static unsigned int get_rr_interval_fair(struct rq *rq, struct task_struct *task)
 {
 	struct sched_entity *se = &task->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	unsigned int rr_interval = 0;
 
 	/*
 	 * Time slice is 0 for SCHED_OTHER tasks that are on an otherwise
-	 * idle runqueue:
+	 * idle cfs_rq:
 	 */
-	if (rq->cfs.load.weight)
-		rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));
+	if (cfs_rq->load.weight)
+		rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq, se));
 
 	return rr_interval;
 }
-- 
1.7.9.5