linux-kernel - [PATCH v6 3/9] sched/fair: reset sched_avg last_update_time before set_task

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Message-Id: <20220818124805.601-4-zhouchengming@bytedance.com>
Date:   Thu, 18 Aug 2022 20:47:59 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     vincent.guittot@...aro.org, dietmar.eggemann@....com,
        mingo@...hat.com, peterz@...radead.org, rostedt@...dmis.org,
        bsegall@...gle.com, vschneid@...hat.com
Cc:     linux-kernel@...r.kernel.org, tj@...nel.org,
        Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH v6 3/9] sched/fair: reset sched_avg last_update_time before set_task_rq()

set_task_rq() -> set_task_rq_fair() will try to synchronize the blocked
task's sched_avg when migrate, which is not needed for already detached
task.

task_change_group_fair() will detached the task sched_avg from prev cfs_rq
first, so reset sched_avg last_update_time before set_task_rq() to avoid that.

Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b95599aa951..5a704109472a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11824,12 +11824,12 @@ void init_cfs_rq(struct cfs_rq *cfs_rq)
 static void task_change_group_fair(struct task_struct *p)
 {
 	detach_task_cfs_rq(p);
-	set_task_rq(p, task_cpu(p));
 
 #ifdef CONFIG_SMP
 	/* Tell se's cfs_rq has been changed -- migrated */
 	p->se.avg.last_update_time = 0;
 #endif
+	set_task_rq(p, task_cpu(p));
 	attach_task_cfs_rq(p);
 }
 
-- 
2.37.2