linux-kernel - Re: [PATCH 12/15] sched,fair: flatten update

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Date:   Tue, 27 Aug 2019 12:37:38 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org
Cc:     kernel-team@...com, pjt@...gle.com, peterz@...radead.org,
        mingo@...hat.com, morten.rasmussen@....com, tglx@...utronix.de,
        mgorman@...hsingularity.net, vincent.guittot@...aro.org
Subject: Re: [PATCH 12/15] sched,fair: flatten update_curr functionality

On 22/08/2019 04:17, Rik van Riel wrote:
> Make it clear that update_curr only works on tasks any more.
> 
> There is no need for task_tick_fair to call it on every sched entity up
> the hierarchy, so move the call out of entity_tick.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>`
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  kernel/sched/fair.c | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index fa8e88731821..5cfa3dbeba49 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -872,10 +872,11 @@ static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
>  static void update_curr(struct cfs_rq *cfs_rq)
>  {
>  	struct sched_entity *curr = cfs_rq->curr;
> +	struct task_struct *curtask;
>  	u64 now = rq_clock_task(rq_of(cfs_rq));
>  	u64 delta_exec;
>  
> -	if (unlikely(!curr))
> +	if (unlikely(!curr) || !entity_is_task(curr))
>  		return;

Shouldn't this be

-       if (unlikely(!curr) || !entity_is_task(curr))
+       if (unlikely(!curr))
                return;

+       BUG_ON(!entity_is_task(curr));

IMHO, cfs_rq->curr can only be a task with your changes.