linux-kernel - Re: [PATCH 2/6] sched_ext: Open-code task_linked_on

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Message-ID: <Zo5Mv4aIe2wDSHyJ@gpd>
Date: Wed, 10 Jul 2024 10:56:31 +0200
From: Andrea Righi <righi.andrea@...il.com>
To: Tejun Heo <tj@...nel.org>
Cc: void@...ifault.com, linux-kernel@...r.kernel.org, kernel-team@...a.com,
	schatzberg.dan@...il.com, mingo@...hat.com, peterz@...radead.org,
	changwoo@...lia.com
Subject: Re: [PATCH 2/6] sched_ext: Open-code task_linked_on_dsq()

On Tue, Jul 09, 2024 at 11:21:08AM -1000, Tejun Heo wrote:
> task_linked_on_dsq() exists as a helper becauase it used to test both the

small nit: becauase -> because.

> rbtree and list nodes. It now only tests the list node and the list node
> will soon be used for something else too. The helper doesn't improve
> anything materially and the naming will become confusing. Open-code the list
> node testing and remove task_linked_on_dsq()
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: David Vernet <void@...ifault.com>
> ---
>  kernel/sched/ext.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index f16d72d72635..52340ac8038f 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -1572,18 +1572,13 @@ static void task_unlink_from_dsq(struct task_struct *p,
>  	list_del_init(&p->scx.dsq_list.node);
>  }
>  
> -static bool task_linked_on_dsq(struct task_struct *p)
> -{
> -	return !list_empty(&p->scx.dsq_list.node);
> -}
> -
>  static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
>  {
>  	struct scx_dispatch_q *dsq = p->scx.dsq;
>  	bool is_local = dsq == &rq->scx.local_dsq;
>  
>  	if (!dsq) {
> -		WARN_ON_ONCE(task_linked_on_dsq(p));
> +		WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node));
>  		/*
>  		 * When dispatching directly from the BPF scheduler to a local
>  		 * DSQ, the task isn't associated with any DSQ but
> @@ -1604,7 +1599,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
>  	*/
>  	if (p->scx.holding_cpu < 0) {
>  		/* @p must still be on @dsq, dequeue */
> -		WARN_ON_ONCE(!task_linked_on_dsq(p));
> +		WARN_ON_ONCE(list_empty(&p->scx.dsq_list.node));
>  		task_unlink_from_dsq(p, dsq);
>  		dsq_mod_nr(dsq, -1);
>  	} else {
> @@ -1614,7 +1609,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
>  		 * holding_cpu which tells dispatch_to_local_dsq() that it lost
>  		 * the race.
>  		 */
> -		WARN_ON_ONCE(task_linked_on_dsq(p));
> +		WARN_ON_ONCE(!list_empty(&p->scx.dsq_list.node));
>  		p->scx.holding_cpu = -1;
>  	}
>  	p->scx.dsq = NULL;
> -- 
> 2.45.2