[PATCH v4 2/2] sched/fair: Keep load_avg in sync after reweighting

[Zicheng Qu]

se->avg.load_avg is derived from se->avg.load_sum and se_weight().
When the fair load weight is rebuilt while switching back to fair,
load_avg must be rebuilt too before the entity is attached.

Factor the existing reweight_entity() calculation into a helper and use
it from switching_to_fair() as well.

Link: https://lore.kernel.org/all/20260530050609.0D0FB1F00893@xxxxxxxxxxxxxxx/
Signed-off-by: Zicheng Qu <quzicheng@xxxxxxxxxx>
---
Changes in v4:
- New patch.

 kernel/sched/fair.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index edb11065a9fc..19270132a506 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4663,6 +4663,13 @@ rescale_entity(struct sched_entity *se, unsigned long weight, bool rel_vprot)
 		se->vprot = div64_long(se->vprot * old_weight, weight);
 }
 
+static inline void update_load_avg_after_reweight(struct sched_entity *se)
+{
+	u32 divider = get_pelt_divider(&se->avg);
+
+	se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
+}
+
 static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 			    unsigned long weight)
 {
@@ -4692,11 +4699,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 	rescale_entity(se, weight, rel_vprot);
 
 	update_load_set(&se->load, weight);
-
-	do {
-		u32 divider = get_pelt_divider(&se->avg);
-		se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum, divider);
-	} while (0);
+	update_load_avg_after_reweight(se);
 
 	enqueue_load_avg(cfs_rq, se);
 	if (se->on_rq) {
@@ -15005,6 +15008,7 @@ static void switching_to_fair(struct rq *rq, struct task_struct *p)
 	 * Rebuild it before the task is enqueued.
 	 */
 	set_load_weight(p, false);
+	update_load_avg_after_reweight(&p->se);
 }
 
 static void switched_from_fair(struct rq *rq, struct task_struct *p)
-- 
2.53.0