Linus,
Please pull the latest sched-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git
sched-urgent-for-linus
# HEAD: 2548d546d40c0014efdde88a53bf7896e917dcce nohz/full, sched/rt: Fix
missed tick-reenabling bug in sched_can_stop_tick()
This tree 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.
Thanks,
Ingo
------------------>
Peter Zijlstra (1):
nohz/full, sched/rt: Fix missed tick-reenabling bug in
sched_can_stop_tick()
kernel/sched/core.c | 29 ++++++++++++++++-------------
1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8b489fcac37b..d1f7149f8704 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;
