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@bytedance.com>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.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

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5d6da83c44af70ede7bfd0fd6d1ef8a3b3e0402c
Gitweb:        https://git.kernel.org/tip/5d6da83c44af70ede7bfd0fd6d1ef8a3b3e0402c
Author:        Chengming Zhou <zhouchengming@bytedance.com>
AuthorDate:    Thu, 18 Aug 2022 20:47:59 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 23 Aug 2022 11:01:18 +02:00

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@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20220818124805.601-4-zhouchengming@bytedance.com
---
 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 2c0eb2a..e4c0929 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -11660,12 +11660,12 @@ 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);
 }