[PATCH v6 08/23] 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 FAIR task 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 1fb1c17e8387..aa4201bb8082 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1473,6 +1473,10 @@ bool sched_can_stop_tick(struct rq *rq)
 			return false;
 	}
 
+	/* Keep the tick running until CFS tasks are pushed out*/
+	if (!cpu_preferred(rq->cpu) && rq->cfs.h_nr_queued)
+		return false;
+
 	return true;
 }
 #endif /* CONFIG_NO_HZ_FULL */
-- 
2.47.3