[PATCH v3 10/20] sched/core: Keep tick on non-preferred CPUs until tasks are out

[Shrikanth Hegde <sshegde@linux.ibm.com>]

Enable tick on nohz full CPU when it is marked as non-preferred.
If there in no CFS/RT running there, disable the tick to save the power.

Steal time handling code will call tick_nohz_dep_set_cpu with
TICK_DEP_BIT_SCHED for moving the task out of nohz_full CPU fast.

Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 kernel/sched/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 292d4e7db0fd..86fa4bfaead0 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1420,6 +1420,10 @@ bool sched_can_stop_tick(struct rq *rq)
 	if (rq->dl.dl_nr_running)
 		return false;
 
+	/* Keep the tick running until both RT and CFS are pushed out*/
+	if (!cpu_preferred(rq->cpu) && (rq->rt.rt_nr_running || rq->cfs.h_nr_queued))
+		return false;
+
 	/*
 	 * If there are more than one RR tasks, we need the tick to affect the
 	 * actual RR behaviour.
-- 
2.47.3