linux-kernel - [PATCH] sched/idle: disable tick in idle=poll idle entry

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Date:   Wed, 7 Jun 2023 22:10:46 -0300
From:   Marcelo Tosatti <mtosatti@...hat.com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] sched/idle: disable tick in idle=poll idle entry

Commit a5183862e76fdc25f36b39c2489b816a5c66e2e5 
("tick/nohz: Conditionally restart tick on idle exit") allows
a nohz_full CPU to enter idle and return from it with the 
scheduler tick disabled (since the tick might be undesired noise).

The idle=poll case still unconditionally restarts the tick when entering
idle.

To reduce the noise for that case as well, stop the tick when entering
idle, for the idle=poll case.

tick_nohz_idle_exit (called if the NEED_RESCHED bit is set) 
is responsible for re-enabling the tick when necessary. 

Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>

---

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 342f58a329f5..fdc240988ea9 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -276,7 +276,7 @@ static void do_idle(void)
 		 * idle as we know that the IPI is going to arrive right away.
 		 */
 		if (cpu_idle_force_poll || tick_check_broadcast_expired()) {
-			tick_nohz_idle_restart_tick();
+			tick_nohz_idle_stop_tick();
 			cpu_idle_poll();
 		} else {
 			cpuidle_idle_call();