[PATCH] sched/idle: Stop the tick when no cpuidle driver is available

[Christian Loehle <christian.loehle@arm.com>]

Commit f4c31b07b136 ("sched: idle: Consolidate the handling of two
special cases") changed the no-cpuidle-driver path to use the previous
tick wakeup heuristic.

Oracle reported a substantial sysbench regression on small OCI VM shapes
with no cpuidle driver available. Reverting the commit recovered the lost
performance.

Restore the previous tick handling for the no-driver case while retaining
the heuristic for the single-state cpuidle case.

Fixes: f4c31b07b136 ("sched: idle: Consolidate the handling of two special cases")
Reported-by: Joseph Salisbury <joseph.salisbury@oracle.com>
Closes: https://lore.kernel.org/all/096b42fa-107f-450d-b3b1-03bcad3f1e04@oracle.com/
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
---
Here's the actual patch, I'd still be curious about why this happens here...

 kernel/sched/idle.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 052435f4d3e3..a814f9d5759f 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -194,7 +194,7 @@ static void cpuidle_idle_call(bool stop_tick)
 	}
 
 	if (cpuidle_not_available(drv, dev)) {
-		idle_call_stop_or_retain_tick(stop_tick);
+		tick_nohz_idle_stop_tick();
 
 		default_idle_call();
 		goto exit_idle;
-- 
2.34.1