linux-kernel - Re: [PATCH] sched: fix bad task migration for rt tasks

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Date:   Fri, 24 Jun 2022 11:56:38 +0100
From:   Valentin Schneider <vschneid@...hat.com>
To:     Schspa Shi <schspa@...il.com>, 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,
        bristot@...hat.com
Cc:     linux-kernel@...r.kernel.org, zhaohui.shi@...izon.ai,
        Schspa Shi <schspa@...il.com>
Subject: Re: [PATCH] sched: fix bad task migration for rt tasks

On 24/06/22 02:29, Schspa Shi wrote:
> @@ -1998,12 +1998,15 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
>  			 * the mean time, task could have
>  			 * migrated already or had its affinity changed.
>  			 * Also make sure that it wasn't scheduled on its rq.
> +			 * It is possible the task has running for a while,
> +			 * And we check task migration disable flag again.
>  			 */
>  			if (unlikely(task_rq(task) != rq ||
>  				     !cpumask_test_cpu(lowest_rq->cpu, &task->cpus_mask) ||

cf. 95158a89dd50 ("sched,rt: Use the full cpumask for balancing"), this
made sense to me back then but not so much anymore... Shouldn't this have
remained a ->cpus_ptr check?

I'm going to revisit that commit, I evicted too much of it.

>  				     task_running(rq, task) ||
>  				     !rt_task(task) ||
> -				     !task_on_rq_queued(task))) {
> +				     !task_on_rq_queued(task) ||
> +				     is_migration_disabled(task))) {
>  
>  				double_unlock_balance(rq, lowest_rq);
>  				lowest_rq = NULL;
> -- 
> 2.24.3 (Apple Git-128)