linux-kernel - [PATCH v2] time/tick-sched: idle load balancing when nohz

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Date: Wed,  8 May 2024 18:26:21 +0100
From: Levi Yun <ppbuk5246@...il.com>
To: anna-maria@...utronix.de,
	frederic@...nel.org,
	mingo@...nel.org,
	tglx@...utronix.de,
	Markus.Elfring@....de
Cc: linux-kernel@...r.kernel.org,
	Levi Yun <ppbuk5246@...il.com>
Subject: [PATCH v2] time/tick-sched: idle load balancing when nohz_full cpu becomes idle.

When nohz_full CPU stops tick in tick_nohz_irq_exit(),
It wouldn't be chosen to perform idle load balancing bacause it doesn't
call nohz_balance_enter_idle() in tick_nohz_idle_stop_tick() when it
becomes idle.

tick_nohz_idle_stop_tick() is only called in idle state and
nohz_balance_enter_idle() tracks the CPU is part of nohz.idle_cpus_mask
with rq->nohz_tick_stopped.

So, nohz_balance_enter_idle() could be called safely without !was_stooped
check.

Fixes: 0e7767687fda ("time: tick-sched: Reorganize idle tick management code")
Signed-off-by: Levi Yun <ppbuk5246@...il.com>
---
 kernel/time/tick-sched.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 71a792cd8936..31a4cd89782f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -1228,8 +1228,10 @@ void tick_nohz_idle_stop_tick(void)
 		ts->idle_sleeps++;
 		ts->idle_expires = expires;

-		if (!was_stopped && tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
-			ts->idle_jiffies = ts->last_jiffies;
+		if (tick_sched_flag_test(ts, TS_FLAG_STOPPED)) {
+			if (!was_stopped)
+				ts->idle_jiffies = ts->last_jiffies;
+
 			nohz_balance_enter_idle(cpu);
 		}
 	} else {
--
2.41.0