Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

Pull scheduler fix from Ingo Molnar:
 "This contains a single fix that fixes a nohz tick stopping bug when
  mixed-poliocy SCHED_FIFO and SCHED_RR tasks are present on a runqueue"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick()

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b489fcac37bd9d829439feb08d8bac1354c7e71..d1f7149f870439d65b9cfcfbc27d4160bbb1672f 100644 (file)
--- 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;