linux-kernel - Re: [PATCH 2/2][v2] sched: Extract the task putting code from pick_next

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Date:   Mon, 20 Apr 2020 18:44:29 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2][v2] sched: Extract the task putting code from pick_next_task()


On 20/04/20 16:01, Chen Yu wrote:
> Introduce a new function finish_prev_task() to do the balance
> when necessary, and then put previous task back to the run queue.
> This function is extracted from pick_next_task() to prepare for
> future usage by other type of task picking logic.
>
> No functional change.
>

With the absolutely tiny nit below:

Reviewed-by: Valentin Schneider <valentin.schneider@....com>

> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
>  kernel/sched/core.c | 39 +++++++++++++++++++++++----------------
>  1 file changed, 23 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 3a61a3b8eaa9..bf59a5cf030c 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -3904,6 +3904,28 @@ static inline void schedule_debug(struct task_struct *prev, bool preempt)
>       schedstat_inc(this_rq()->sched_count);
>  }
>
> +static void finish_prev_task(struct rq *rq, struct task_struct *prev,
> +			     struct rq_flags *rf)
> +{
> +	const struct sched_class *class;
> +#ifdef CONFIG_SMP

Nit: I would've put that declaration within the ifdef, given it isn't used
outside of it.

> +	/*
> +	 * We must do the balancing pass before put_next_task(), such
> +	 * that when we release the rq->lock the task is in the same
> +	 * state as before we took rq->lock.
> +	 *
> +	 * We can terminate the balance pass as soon as we know there is
> +	 * a runnable task of @class priority or higher.
> +	 */
> +	for_class_range(class, prev->sched_class, &idle_sched_class) {
> +		if (class->balance(rq, prev, rf))
> +			break;
> +	}
> +#endif
> +
> +	put_prev_task(rq, prev);
> +}
> +
>  /*
>   * Pick up the highest-prio task:
>   */