linux-kernel - Re: [RFC][PATCH 6/6] sched: Cleanup sched

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Message-ID: <20241030154551.GN14555@noisy.programming.kicks-ass.net>
Date: Wed, 30 Oct 2024 16:45:51 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: mingo@...nel.org
Cc: juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, tj@...nel.org,
	void@...ifault.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 6/6] sched: Cleanup sched_delayed handling for class
 switches

On Wed, Oct 30, 2024 at 04:13:01PM +0100, Peter Zijlstra wrote:

> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c

> @@ -5202,7 +5200,7 @@ static int scx_ops_enable(struct sched_e
>  	percpu_down_write(&scx_fork_rwsem);
>  	scx_task_iter_start(&sti);
>  	while ((p = scx_task_iter_next_locked(&sti))) {
> -		unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
> +		unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
>  		const struct sched_class *old_class = p->sched_class;
>  		const struct sched_class *new_class =
>  			__setscheduler_class(p->policy, p->prio);
> @@ -5210,9 +5208,7 @@ static int scx_ops_enable(struct sched_e
>  		if (old_class != new_class)
>  			queue_flags |= DEQUEUE_CLASS;
>  
> -		if (old_class != new_class && p->se.sched_delayed)
> -			dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED);
> -
> +		update_rq_clock(task_rq(p));
>  		scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
>  			p->scx.slice = SCX_SLICE_DFL;
>  			p->sched_class = new_class;

TJ, strictly speaking you should probably do a __balance_callbacks() in
__scx_task_irq_rq_unlock(). The various switched_from() methods like to
queue_balance_callback().

I think you're currently good by the fact that only RT/DL do this, and
you're not touching those in these loops.