linux-kernel - Re: [RFC PATCH v15 5/7] sched: Add an initial sketch of the find_proxy

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Message-ID: <20250317134837.GC36386@noisy.programming.kicks-ass.net>
Date: Mon, 17 Mar 2025 14:48:37 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: John Stultz <jstultz@...gle.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Valentin Schneider <vschneid@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Metin Kaya <Metin.Kaya@....com>,
	Xuewen Yan <xuewen.yan94@...il.com>,
	K Prateek Nayak <kprateek.nayak@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Suleiman Souhlal <suleiman@...gle.com>, kernel-team@...roid.com
Subject: Re: [RFC PATCH v15 5/7] sched: Add an initial sketch of the
 find_proxy_task() function

On Wed, Mar 12, 2025 at 03:11:35PM -0700, John Stultz wrote:
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4b8e33c615b12..2d418e0efecc5 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1479,8 +1479,19 @@ enqueue_task_rt(struct rq *rq, struct task_struct *p, int flags)
>  
>  	enqueue_rt_entity(rt_se, flags);
>  
> -	if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
> -		enqueue_pushable_task(rq, p);
> +	/*
> +	 * Current can't be pushed away. Selected is tied to current,
> +	 * so don't push it either.
> +	 */
> +	if (task_current(rq, p) || task_current_donor(rq, p))
> +		return;
> +	/*
> +	 * Pinned tasks can't be pushed.
> +	 */
> +	if (p->nr_cpus_allowed == 1)
> +		return;
> +
> +	enqueue_pushable_task(rq, p);
>  }
>  

As per always, deadline.c will have the exact same logic.