linux-kernel - Re: [PATCH 1/8] sched: introduce task_se_h

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Date:   Wed, 19 Jun 2019 14:52:36 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Rik van Riel <riel@...riel.com>, peterz@...radead.org
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org, kernel-team@...com,
        morten.rasmussen@....com, tglx@...utronix.de,
        dietmar.eggeman@....com, mgorman@...hsingularity.com,
        vincent.guittot@...aro.org
Subject: Re: [PATCH 1/8] sched: introduce task_se_h_load helper

On 6/12/19 9:32 PM, Rik van Riel wrote:
> Sometimes the hierarchical load of a sched_entity needs to be calculated.
> Split out task_h_load into a task_se_h_load that takes a sched_entity pointer
> as its argument, and a task_h_load wrapper that calls task_se_h_load.
> 
> No functional changes.
> 
> Signed-off-by: Rik van Riel <riel@...riel.com>
> ---
>  kernel/sched/fair.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index f35930f5e528..df624f7a68e7 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -706,6 +706,7 @@ static u64 sched_vslice(struct cfs_rq *cfs_rq, struct sched_entity *se)
>  #ifdef CONFIG_SMP
>  
>  static int select_idle_sibling(struct task_struct *p, int prev_cpu, int cpu);
> +static unsigned long task_se_h_load(struct sched_entity *se);
>  static unsigned long task_h_load(struct task_struct *p);
>  static unsigned long capacity_of(int cpu);
>  
> @@ -7833,14 +7834,19 @@ static void update_cfs_rq_h_load(struct cfs_rq *cfs_rq)
>  	}
>  }
>  
> -static unsigned long task_h_load(struct task_struct *p)
> +static unsigned long task_se_h_load(struct sched_entity *se)
>  {
> -	struct cfs_rq *cfs_rq = task_cfs_rq(p);
> +	struct cfs_rq *cfs_rq = cfs_rq_of(se);
>  
>  	update_cfs_rq_h_load(cfs_rq);
> -	return div64_ul(p->se.avg.load_avg * cfs_rq->h_load,
> +	return div64_ul(se->avg.load_avg * cfs_rq->h_load,
>  			cfs_rq_load_avg(cfs_rq) + 1);
>  }

I wonder if this is necessary. I placed a BUG_ON(!entity_is_task(se))
into task_se_h_load() after I applied the whole patch-set and ran some
taskgroup related testcases. It didn't hit.

So why not use task_h_load(task_of(se)) instead?

[...]