Merge branch 'sched/urgent' into sched/core, to pick up fixes before applying new changes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 16 insertions, 13 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index adcafda7ffc8..c82ca6eccfec 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -596,17 +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)
@@ -615,8 +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;