linux-kernel - [PATCH] sched/fair: Simplify continue

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Date: Mon, 25 Mar 2024 21:09:26 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org
Cc: sshegde@...ux.ibm.com, dietmar.eggemann@....com, qyousef@...alina.io,
        linux-kernel@...r.kernel.org, vschneid@...hat.com, joshdon@...gle.com,
        riel@...riel.com
Subject: [PATCH] sched/fair: Simplify continue_balancing for newidle

newidle(CPU_NEWLY_IDLE) balancing doesn't stop the load balancing if the
continue_balancing flag is reset. Other two balancing (IDLE, BUSY) do
that. newidle balance stops the load balancing if rq has a task or there
is wakeup pending. The same checks are present in should_we_balance for
newidle. Hence use the return value and simplify continue_balancing
mechanism for newidle. Update the comment surrounding it as well.

No change in functionality intended.

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
 kernel/sched/fair.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f00cb66cc479..d80535df8f03 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12307,6 +12307,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
 {
 	unsigned long next_balance = jiffies + HZ;
 	int this_cpu = this_rq->cpu;
+	int continue_balancing = 1;
 	u64 t0, t1, curr_cost = 0;
 	struct sched_domain *sd;
 	int pulled_task = 0;
@@ -12321,8 +12322,9 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
 		return 0;

 	/*
-	 * We must set idle_stamp _before_ calling idle_balance(), such that we
-	 * measure the duration of idle_balance() as idle time.
+	 * We must set idle_stamp _before_ calling sched_balance_rq()
+	 * for CPU_NEWLY_IDLE, such that we measure the this duration
+	 * as idle time.
 	 */
 	this_rq->idle_stamp = rq_clock(this_rq);

@@ -12361,7 +12363,6 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)

 	rcu_read_lock();
 	for_each_domain(this_cpu, sd) {
-		int continue_balancing = 1;
 		u64 domain_cost;

 		update_next_balance(sd, &next_balance);
@@ -12387,8 +12388,7 @@ static int sched_balance_newidle(struct rq *this_rq, struct rq_flags *rf)
 		 * Stop searching for tasks to pull if there are
 		 * now runnable tasks on this rq.
 		 */
-		if (pulled_task || this_rq->nr_running > 0 ||
-		    this_rq->ttwu_pending)
+		if (pulled_task || !continue_balancing)
 			break;
 	}
 	rcu_read_unlock();
--
2.39.3