linux-kernel - [PATCH] sched/idle: Prevent stopping the tick when there is no cpuidle driver

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Date: Fri, 15 Dec 2023 14:05:01 +0100
From: Anna-Maria Behnsen <anna-maria@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] sched/idle: Prevent stopping the tick when there is no cpuidle driver

When there is no cpuidle driver, the system tries to stop the tick even if
the system is fully loaded. But stopping the tick is not for free and it
decreases performance on a fully loaded system. As there is no (cpuidle)
framework which brings CPU in a power saving state when nothing needs to be
done, there is also no power saving benefit when stopping the tick.

Therefore do not stop the tick when there is no cpuidle driver.

Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
---
 kernel/sched/idle.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 565f8374ddbb..fd111686aaf3 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -165,8 +165,6 @@ static void cpuidle_idle_call(void)
 	 */
 
 	if (cpuidle_not_available(drv, dev)) {
-		tick_nohz_idle_stop_tick();
-
 		default_idle_call();
 		goto exit_idle;
 	}
-- 
2.39.2