linux-kernel - Re: [PATCH v2] sched/fair: Fix unfairness caused by stalled tg_load_avg

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Message-ID: <20250826081731.20384-1-xupengbo@oppo.com>
Date: Tue, 26 Aug 2025 16:17:31 +0800
From: xupengbo <xupengbo@...o.com>
To: <xupengbo@...o.com>
CC: <aaron.lu@...el.com>, <bsegall@...gle.com>, <cgroups@...r.kernel.org>,
	<dietmar.eggemann@....com>, <juri.lelli@...hat.com>,
	<linux-kernel@...r.kernel.org>, <mgorman@...e.de>, <mingo@...hat.com>,
	<peterz@...radead.org>, <rostedt@...dmis.org>, <vincent.guittot@...aro.org>,
	<void@...ifault.com>, <vschneid@...hat.com>, <xupengbo1029@....com>,
	<ziqianlu@...edance.com>
Subject: Re: [PATCH v2] sched/fair: Fix unfairness caused by stalled tg_load_avg_contrib when the last task migrates out.

>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.

I already sent an updated patch v3.
Link: https://lore.kernel.org/cgroups/20250826075743.19106-1-xupengbo@oppo.com/

Thanks,
xupengbo