linux-kernel - Re: [PATCH] sched/rt: optimize checking group rt scheduler constraints

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Message-ID: <20200125153211.GP2437@uranus>
Date:   Sat, 25 Jan 2020 18:32:11 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-kernel@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH] sched/rt: optimize checking group rt scheduler
 constraints

On Sat, Jan 25, 2020 at 05:50:38PM +0300, Konstantin Khlebnikov wrote:
...
> -/* Must be called with tasklist_lock held */
>  static inline int tg_has_rt_tasks(struct task_group *tg)
>  {
> -	struct task_struct *g, *p;
> +	struct task_struct *task;
> +	struct css_task_iter it;
> +	int ret = 0;
>  
>  	/*
>  	 * Autogroups do not have RT tasks; see autogroup_create().
> @@ -2407,12 +2408,12 @@ static inline int tg_has_rt_tasks(struct task_group *tg)
>  	if (task_group_is_autogroup(tg))
>  		return 0;
>  
> -	for_each_process_thread(g, p) {
> -		if (rt_task(p) && task_group(p) == tg)
> -			return 1;
> -	}
> +	css_task_iter_start(&tg->css, 0, &it);
> +	while (!ret && (task = css_task_iter_next(&it)))
> +		ret |= rt_task(task);

Plain 'ret = rt_task(task);' won't work?

> +	css_task_iter_end(&it);
>  
> -	return 0;
> +	return ret;
>  }