[RFC PATCH v4 09/17] sched/core: Add support for nohz_full CPUs

[Shrikanth Hegde]

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

In addition to this, arch specific code which enables the paravirt CPU
should 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 at 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 90fc04d84b74..73d1d49a3c72 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1336,6 +1336,10 @@ bool sched_can_stop_tick(struct rq *rq)
 {
 	int fifo_nr_running;
 
+	/* Keep the tick running until both RT and CFS are pushed out*/
+	if (cpu_paravirt(rq->cpu) && (rq->rt.rt_nr_running || rq->cfs.h_nr_queued))
+		return false;
+
 	/* Deadline tasks, even if single, need the tick */
 	if (rq->dl.dl_nr_running)
 		return false;
-- 
2.47.3