linux-kernel - [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in reweight

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Message-Id: <20240720051248.59608-1-zhouchuyi@bytedance.com>
Date: Sat, 20 Jul 2024 13:12:48 +0800
From: Chuyi Zhou <zhouchuyi@...edance.com>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org,
	dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com
Cc: chengming.zhou@...ux.dev,
	linux-kernel@...r.kernel.org,
	Chuyi Zhou <zhouchuyi@...edance.com>
Subject: [PATCH v2] sched/fair: Sync se's load_avg with cfs_rq in reweight_task

In reweight_task(), there are two situations:

1. The task was on_rq, then the task's load_avg is accurate because we
synchronized it with cfs_rq through update_load_avg() in dequeue_task().

2. The task is sleeping, its load_avg might not have been updated for some
time, which can result in inaccurate dequeue_load_avg() in
reweight_entity().

This patch solves this by using update_load_avg() to synchronize the
load_avg of se with cfs_rq. For tasks were on_rq, since we already update
load_avg to accurate values in dequeue_task(), this change will not have
other effects due to the short time interval between the two updates.

Signed-off-by: Chuyi Zhou <zhouchuyi@...edance.com>
---
Changes in v2:
- change the description in commit log.
- use update_load_avg() in reweight_task() rather than in reweight_entity
suggested by chengming.
- Link to v1: https://lore.kernel.org/lkml/20240716150840.23061-1-zhouchuyi@bytedance.com/
---
 kernel/sched/fair.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9057584ec06d..b1e07ce90284 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3835,12 +3835,15 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 	}
 }
 
+static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags);
+
 void reweight_task(struct task_struct *p, const struct load_weight *lw)
 {
 	struct sched_entity *se = &p->se;
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	struct load_weight *load = &se->load;
 
+	update_load_avg(cfs_rq, se, 0);
 	reweight_entity(cfs_rq, se, lw->weight);
 	load->inv_weight = lw->inv_weight;
 }
-- 
2.20.1