linux-kernel - Re: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs pick_next

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Date:   Mon, 29 Jul 2019 11:25:19 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org,
        dietmar.eggemann@....com, luca.abeni@...tannapisa.it,
        bristot@...hat.com, balsini@...roid.com, dvyukov@...gle.com,
        tglx@...utronix.de, vpillai@...italocean.com, rostedt@...dmis.org
Subject: Re: [RFC][PATCH 04/13] sched/{rt,deadline}: Fix set_next_task vs
 pick_next_task

Hi,

On 26/07/19 16:54, Peter Zijlstra wrote:
> Because pick_next_task() implies set_curr_task() and some of the
> details haven't matter too much, some of what _should_ be in
> set_curr_task() ended up in pick_next_task, correct this.
> 
> This prepares the way for a pick_next_task() variant that does not
> affect the current state; allowing remote picking.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>  kernel/sched/deadline.c |   23 ++++++++++++-----------
>  kernel/sched/rt.c       |   27 ++++++++++++++-------------
>  2 files changed, 26 insertions(+), 24 deletions(-)
> 
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1694,12 +1694,21 @@ static void start_hrtick_dl(struct rq *r
>  }
>  #endif
>  
> -static inline void set_next_task(struct rq *rq, struct task_struct *p)
> +static void set_next_task_dl(struct rq *rq, struct task_struct *p)
>  {
>  	p->se.exec_start = rq_clock_task(rq);
>  
>  	/* You can't push away the running task */
>  	dequeue_pushable_dl_task(rq, p);
> +
> +	if (hrtick_enabled(rq))
> +		start_hrtick_dl(rq, p);
> +
> +	if (rq->curr->sched_class != &dl_sched_class)
> +		update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 0);
> +
> +	if (rq->curr != p)
> +		deadline_queue_push_tasks(rq);

It's a minor thing, but I was wondering why you added the check on curr.
deadline_queue_push_tasks() already checks if are there pushable tasks,
plus curr can still be of a different class at this point?

Thanks,

Juri