linux-kernel - Re: [PATCH 2/3] sched/deadline: avoid redundant check for boosted task

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Message-ID: <Zp9v8gJ8nqyLkL1m@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 23 Jul 2024 10:55:14 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Wander Lairson Costa <wander@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	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>,
	Valentin Schneider <vschneid@...hat.com>,
	"open list:SCHEDULER" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] sched/deadline: avoid redundant check for boosted
 task

Hi Wander,

On 22/07/24 10:29, Wander Lairson Costa wrote:
> enqueue_dl_entity only calls setup_new_dl_entity if the task is not
> boosted, so the WARN_ON check is unnecessary.
> 
> Signed-off-by: Wander Lairson Costa <wander@...hat.com>
> ---
>  kernel/sched/deadline.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 312e8fa7ce94..908d5ce79425 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -785,12 +785,11 @@ static inline void replenish_dl_new_period(struct sched_dl_entity *dl_se,
>   * one, and to (try to!) reconcile itself with its own scheduling
>   * parameters.
>   */
> -static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> +static inline void __setup_new_dl_entity(struct sched_dl_entity *dl_se)
>  {
>  	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>  	struct rq *rq = rq_of_dl_rq(dl_rq);
>  
> -	WARN_ON(is_dl_boosted(dl_se));
>  	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
>  
>  	/*
> @@ -809,6 +808,12 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
>  	replenish_dl_new_period(dl_se, rq);
>  }
>  
> +static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> +{
> +	WARN_ON(is_dl_boosted(dl_se));
> +	__setup_new_dl_entity(dl_se);
> +}
> +

So, the other call path is from dl_server_start() and for this we know
the entity is not boosted either. We could probably just remove the
WARN_ON w/o the additional wrapper function. That said, considering it's
not fast path, I wonder if we actually want to leave the WARN_ON where
it is, so that we can catch potential future erroneous usages?

Thanks,
Juri