Re: [PATCH v2] sched/fair: Fix unfairness caused by stalled tg_load_avg_contrib when the last task migrates out.

[Aaron Lu <ziqianlu@bytedance.com>]

Hi xupengbo,

On Wed, Aug 06, 2025 at 04:38:10PM +0800, xupengbo wrote:
... ... 
> 
> It actually becomes:
>     if (cfs_rq->tg_load_avg_contrib > 0)
> if cfs_rq->tg_load_avg_contrib == 0 , it will be false. As it is an unsigned
> long, this condition is equivalent to :
>     if (cfs_rq->tg_load_avg_contrib)

I suppose we have reached a conclusion that the right fix is to add a
check of cfs_rq->tg_load_avg_contrib in cfs_rq_is_decayed()? Something
like below:

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af33d107d8034..3ebcb683063f0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4056,6 +4056,9 @@ static inline bool cfs_rq_is_decayed(struct cfs_rq *cfs_rq)
 	if (child_cfs_rq_on_list(cfs_rq))
 		return false;
 
+	if (cfs_rq->tg_load_avg_contrib)
+		return false;
+
 	return true;
 }
 
If you also agree, can you send an updated patch to fix this problem?
Thanks.