linux-kernel - Re: [PATCH -v2 15/17] sched: Fix migrate

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Date:   Mon, 12 Oct 2020 11:56:09 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
        mingo@...nel.org
Cc:     linux-kernel@...r.kernel.org, bigeasy@...utronix.de,
        qais.yousef@....com, swood@...hat.com, valentin.schneider@....com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vincent.donnefort@....com, tj@...nel.org
Subject: Re: [PATCH -v2 15/17] sched: Fix migrate_disable() vs rt/dl balancing

On 05/10/2020 16:57, Peter Zijlstra wrote:

[...]

> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1859,7 +1859,7 @@ static struct task_struct *pick_next_pus
>   * running task can migrate over to a CPU that is running a task
>   * of lesser priority.
>   */
> -static int push_rt_task(struct rq *rq)
> +static int push_rt_task(struct rq *rq, bool pull)
>  {
>  	struct task_struct *next_task;
>  	struct rq *lowest_rq;
> @@ -1873,6 +1873,34 @@ static int push_rt_task(struct rq *rq)
>  		return 0;
>  
>  retry:
> +	if (is_migration_disabled(next_task)) {
> +		struct task_struct *push_task = NULL;
> +		int cpu;
> +
> +		if (!pull || rq->push_busy)
> +			return 0;

Shouldn't there be the same functionality in push_dl_task(), i.e.
returning 0 earlier for a task with migration_disabled?

[...]