linux-kernel - [PATCH 1/2] sched/fair: skip newidle update stats

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Message-Id: <20211112095857.7016-2-vincent.guittot@linaro.org>
Date:   Fri, 12 Nov 2021 10:58:56 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com
Cc:     joel@...lfernandes.org,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH 1/2] sched/fair: skip newidle update stats

In case we skip the newly idle LB entirely or we abort it because we are
going to exceed the avg_idle, we have to make sure to not start an update
of the blocked load when entering idle

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 13950beb01a2..a162b0ec8963 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10861,7 +10861,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 	int this_cpu = this_rq->cpu;
 	u64 t0, t1, curr_cost = 0;
 	struct sched_domain *sd;
-	int pulled_task = 0;
+	int pulled_task = 0, early_stop = 0;
 
 	update_misfit_status(NULL, this_rq);
 
@@ -10898,8 +10898,16 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 	if (!READ_ONCE(this_rq->rd->overload) ||
 	    (sd && this_rq->avg_idle < sd->max_newidle_lb_cost)) {
 
-		if (sd)
+		if (sd) {
 			update_next_balance(sd, &next_balance);
+
+			/*
+			 * We skip new idle LB because there is not enough
+			 * time before next wake up. Make sure that we will
+			 * not kick NOHZ_NEWILB_KICK
+			 */
+			early_stop = 1;
+		}
 		rcu_read_unlock();
 
 		goto out;
@@ -10918,8 +10926,10 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 
 		update_next_balance(sd, &next_balance);
 
-		if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost)
+		if (this_rq->avg_idle < curr_cost + sd->max_newidle_lb_cost) {
+			early_stop = 1;
 			break;
+		}
 
 		if (sd->flags & SD_BALANCE_NEWIDLE) {
 
@@ -10969,7 +10979,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf)
 
 	if (pulled_task)
 		this_rq->idle_stamp = 0;
-	else
+	else if (!early_stop)
 		nohz_newidle_balance(this_rq);
 
 	rq_repin_lock(this_rq, rf);
-- 
2.17.1