linux-kernel - Re: [PATCH 1/2] sched_ext: Factor out local_dsq_post_enq() from dispatch

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Message-ID: <aTtSeZ0dAadWj7Wi@gpd4>
Date: Fri, 12 Dec 2025 00:23:37 +0100
From: Andrea Righi <arighi@...dia.com>
To: Tejun Heo <tj@...nel.org>
Cc: Changwoo Min <changwoo@...lia.com>, David Vernet <void@...ifault.com>,
	Emil Tsalapatis <emil@...alapatis.com>,
	linux-kernel@...r.kernel.org, sched-ext@...ts.linux.dev
Subject: Re: [PATCH 1/2] sched_ext: Factor out local_dsq_post_enq() from
 dispatch_enqueue()

On Thu, Dec 11, 2025 at 12:48:08PM -1000, Tejun Heo wrote:
> Factor out local_dsq_post_enq() which performs post-enqueue handling for
> local DSQs - triggering preemption or resched_curr() if the enqueued task
> has higher priority than the currently running task. No functional change.

Maybe "higher priority" is a bit misleading, how about: "triggering
resched_curr() if SCX_ENQ_PREEMPT is specified or if the current CPU is
idle".

Thanks,
-Andrea

> 
> This will be used by the next patch to fix move_local_task_to_local_dsq().
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>  kernel/sched/ext.c |   34 +++++++++++++++++++---------------
>  1 file changed, 19 insertions(+), 15 deletions(-)
> 
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -975,6 +975,22 @@ static void refill_task_slice_dfl(struct
>  	__scx_add_event(sch, SCX_EV_REFILL_SLICE_DFL, 1);
>  }
>  
> +static void local_dsq_post_enq(struct scx_dispatch_q *dsq, struct task_struct *p,
> +			       u64 enq_flags)
> +{
> +	struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
> +	bool preempt = false;
> +
> +	if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
> +	    rq->curr->sched_class == &ext_sched_class) {
> +		rq->curr->scx.slice = 0;
> +		preempt = true;
> +	}
> +
> +	if (preempt || sched_class_above(&ext_sched_class, rq->curr->sched_class))
> +		resched_curr(rq);
> +}
> +
>  static void dispatch_enqueue(struct scx_sched *sch, struct scx_dispatch_q *dsq,
>  			     struct task_struct *p, u64 enq_flags)
>  {
> @@ -1086,22 +1102,10 @@ static void dispatch_enqueue(struct scx_
>  	if (enq_flags & SCX_ENQ_CLEAR_OPSS)
>  		atomic_long_set_release(&p->scx.ops_state, SCX_OPSS_NONE);
>  
> -	if (is_local) {
> -		struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
> -		bool preempt = false;
> -
> -		if ((enq_flags & SCX_ENQ_PREEMPT) && p != rq->curr &&
> -		    rq->curr->sched_class == &ext_sched_class) {
> -			rq->curr->scx.slice = 0;
> -			preempt = true;
> -		}
> -
> -		if (preempt || sched_class_above(&ext_sched_class,
> -						 rq->curr->sched_class))
> -			resched_curr(rq);
> -	} else {
> +	if (is_local)
> +		local_dsq_post_enq(dsq, p, enq_flags);
> +	else
>  		raw_spin_unlock(&dsq->lock);
> -	}
>  }
>  
>  static void task_unlink_from_dsq(struct task_struct *p,