linux-kernel - [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found

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Message-Id: <20221021061558.34767-2-jiahao.os@bytedance.com>
Date:   Fri, 21 Oct 2022 14:15:57 +0800
From:   Hao Jia <jiahao.os@...edance.com>
To:     mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
        mgorman@...hsingularity.net
Cc:     linux-kernel@...r.kernel.org, Hao Jia <jiahao.os@...edance.com>
Subject: [PATCH 1/2] sched/numa: Stop an exhastive search if an idle core is found

In update_numa_stats() we try to find an idle cpu on the NUMA node,
preferably an idle core. When we find an idle core,
we can stop searching.

Signed-off-by: Hao Jia <jiahao.os@...edance.com>
---
 kernel/sched/fair.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e4a0b8bd941c..b7cbec539c77 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1792,7 +1792,7 @@ static void update_numa_stats(struct task_numa_env *env,
 		ns->nr_running += rq->cfs.h_nr_running;
 		ns->compute_capacity += capacity_of(cpu);
 
-		if (find_idle && !rq->nr_running && idle_cpu(cpu)) {
+		if (find_idle && idle_core < 0 && !rq->nr_running && idle_cpu(cpu)) {
 			if (READ_ONCE(rq->numa_migrate_on) ||
 			    !cpumask_test_cpu(cpu, env->p->cpus_ptr))
 				continue;
@@ -1801,6 +1801,9 @@ static void update_numa_stats(struct task_numa_env *env,
 				ns->idle_cpu = cpu;
 
 			idle_core = numa_idle_core(idle_core, cpu);
+			/* If we find an idle core, stop searching. */
+			if (idle_core >= 0)
+				ns->idle_cpu = idle_core;
 		}
 	}
 	rcu_read_unlock();
@@ -1808,9 +1811,6 @@ static void update_numa_stats(struct task_numa_env *env,
 	ns->weight = cpumask_weight(cpumask_of_node(nid));
 
 	ns->node_type = numa_classify(env->imbalance_pct, ns);
-
-	if (idle_core >= 0)
-		ns->idle_cpu = idle_core;
 }
 
 static void task_numa_assign(struct task_numa_env *env,
-- 
2.37.0