linux-kernel - [PATCH v3 10/10] sched/fair: don't init util/runnable

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Message-Id: <20220801042745.7794-11-zhouchengming@bytedance.com>
Date:   Mon,  1 Aug 2022 12:27:45 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     mingo@...hat.com, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH v3 10/10] sched/fair: don't init util/runnable_avg for !fair task

post_init_entity_util_avg() init task util_avg according to the cpu util_avg
at the time of fork, which will decay when switched_to_fair() some time later,
we'd better to not set them at all in the case of !fair task.

Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
 kernel/sched/fair.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 18e3dff606db..071c159605e7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -833,20 +833,6 @@ void post_init_entity_util_avg(struct task_struct *p)
 	long cpu_scale = arch_scale_cpu_capacity(cpu_of(rq_of(cfs_rq)));
 	long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2;
 
-	if (cap > 0) {
-		if (cfs_rq->avg.util_avg != 0) {
-			sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
-			sa->util_avg /= (cfs_rq->avg.load_avg + 1);
-
-			if (sa->util_avg > cap)
-				sa->util_avg = cap;
-		} else {
-			sa->util_avg = cap;
-		}
-	}
-
-	sa->runnable_avg = sa->util_avg;
-
 	if (p->sched_class != &fair_sched_class) {
 		/*
 		 * For !fair tasks do:
@@ -861,6 +847,20 @@ void post_init_entity_util_avg(struct task_struct *p)
 		se->avg.last_update_time = cfs_rq_clock_pelt(cfs_rq);
 		return;
 	}
+
+	if (cap > 0) {
+		if (cfs_rq->avg.util_avg != 0) {
+			sa->util_avg  = cfs_rq->avg.util_avg * se->load.weight;
+			sa->util_avg /= (cfs_rq->avg.load_avg + 1);
+
+			if (sa->util_avg > cap)
+				sa->util_avg = cap;
+		} else {
+			sa->util_avg = cap;
+		}
+	}
+
+	sa->runnable_avg = sa->util_avg;
 }
 
 #else /* !CONFIG_SMP */
-- 
2.36.1