1 files changed, 34 insertions, 13 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8465eeab8b3..d1f7149f8704 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -321,6 +321,24 @@ static inline void init_hrtick(void)
 }
 #endif	/* CONFIG_SCHED_HRTICK */
 
+/*
+ * cmpxchg based fetch_or, macro so it works for different integer types
+ */
+#define fetch_or(ptr, mask)						\
+	({								\
+		typeof(ptr) _ptr = (ptr);				\
+		typeof(mask) _mask = (mask);				\
+		typeof(*_ptr) _old, _val = *_ptr;			\
+									\
+		for (;;) {						\
+			_old = cmpxchg(_ptr, _val, _val | _mask);	\
+			if (_old == _val)				\
+				break;					\
+			_val = _old;					\
+		}							\
+	_old;								\
+})
+
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
  * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
@@ -578,17 +596,8 @@ bool sched_can_stop_tick(struct rq *rq)
 		return false;
 
 	/*
-	 * FIFO realtime policy runs the highest priority task (after DEADLINE).
-	 * Other runnable tasks are of a lower priority. The scheduler tick
-	 * isn't needed.
-	 */
-	fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
-	if (fifo_nr_running)
-		return true;
-
-	/*
-	 * Round-robin realtime tasks time slice with other tasks at the same
-	 * realtime priority.
+	 * If there are more than one RR tasks, we need the tick to effect the
+	 * actual RR behaviour.
 	 */
 	if (rq->rt.rr_nr_running) {
 		if (rq->rt.rr_nr_running == 1)
@@ -597,8 +606,20 @@ bool sched_can_stop_tick(struct rq *rq)
 			return false;
 	}
 
-	/* Normal multitasking need periodic preemption checks */
-	if (rq->cfs.nr_running > 1)
+	/*
+	 * If there's no RR tasks, but FIFO tasks, we can skip the tick, no
+	 * forced preemption between FIFO tasks.
+	 */
+	fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running;
+	if (fifo_nr_running)
+		return true;
+
+	/*
+	 * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left;
+	 * if there's more than one we need the tick for involuntary
+	 * preemption.
+	 */
+	if (rq->nr_running > 1)
 		return false;
 
 	return true;