linux-kernel - Re: [PATCH v5 2/2] sched/rt: Trying to push current task when target disable migrating

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Message-ID: <20220712102953.02d4a3bd@gandalf.local.home>
Date:   Tue, 12 Jul 2022 10:29:53 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Schspa Shi <schspa@...il.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org,
        zhaohui.shi@...izon.ai
Subject: Re: [PATCH v5 2/2] sched/rt: Trying to push current task when
 target disable migrating

On Tue, 12 Jul 2022 09:31:25 +0800
Schspa Shi <schspa@...il.com> wrote:

> When the task to push disable migration, retry to push the current
> running task on this CPU away, instead doing nothing for this migrate
> disabled task.
> 
> Signed-off-by: Schspa Shi <schspa@...il.com>
> ---
>  kernel/sched/core.c | 6 +++++-
>  kernel/sched/rt.c   | 6 ++++++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index da0bf6fe9ecdc..0b1fefd97d874 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2509,8 +2509,12 @@ int push_cpu_stop(void *arg)
>  	if (p->sched_class->find_lock_rq)
>  		lowest_rq = p->sched_class->find_lock_rq(p, rq);
>  
> -	if (!lowest_rq)
> +	if (!lowest_rq) {

Probably should add a comment reminding us that the find_lock() function
above could have released the rq lock and allow p to schedule and be
preempted again, and that lowest_rq could be NULL because p now has the
migrate_disable flag set and not because it could not find the lowest rq.

-- Steve


> +		if (unlikely(is_migration_disabled(p)))
> +			p->migration_flags |= MDF_PUSH;
> +
>  		goto out_unlock;
> +	}
>  
>  	// XXX validate p is still the highest prio task
>  	if (task_rq(p) == rq) {
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 7c32ba51b6d85..877380e465b7a 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -2136,6 +2136,12 @@ static int push_rt_task(struct rq *rq, bool pull)
>  		 */
>  		task = pick_next_pushable_task(rq);
>  		if (task == next_task) {
> +			/*
> +			 * If next task has now disabled migrating, see if we
> +			 * can push the current task.
> +			 */
> +			if (unlikely(is_migration_disabled(task)))
> +				goto retry;
>  			/*
>  			 * The task hasn't migrated, and is still the next
>  			 * eligible task, but we failed to find a run-queue