linux-kernel - Re: [PATCH v4 03/16] sched/core: uclamp: add CPU's clamp groups accounting

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Message-ID: <20180913191209.GY24082@hirez.programming.kicks-ass.net>
Date:   Thu, 13 Sep 2018 21:12:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Quentin Perret <quentin.perret@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: [PATCH v4 03/16] sched/core: uclamp: add CPU's clamp groups
 accounting

On Tue, Aug 28, 2018 at 02:53:11PM +0100, Patrick Bellasi wrote:
> +static inline void uclamp_cpu_get_id(struct task_struct *p,
> +				     struct rq *rq, int clamp_id)
> +{
> +	struct uclamp_group *uc_grp;
> +	struct uclamp_cpu *uc_cpu;
> +	int clamp_value;
> +	int group_id;
> +
> +	/* Every task must reference a clamp group */
> +	group_id = p->uclamp[clamp_id].group_id;

> +}
> +
> +static inline void uclamp_cpu_put_id(struct task_struct *p,
> +				     struct rq *rq, int clamp_id)
> +{
> +	struct uclamp_group *uc_grp;
> +	struct uclamp_cpu *uc_cpu;
> +	unsigned int clamp_value;
> +	int group_id;
> +
> +	/* New tasks don't have a previous clamp group */
> +	group_id = p->uclamp[clamp_id].group_id;
> +	if (group_id == UCLAMP_NOT_VALID)
> +		return;

*confused*, so on enqueue they must have a group_id, but then on dequeue
they might no longer have?

> +}

> @@ -1110,6 +1313,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
>  	if (!(flags & ENQUEUE_RESTORE))
>  		sched_info_queued(rq, p);
>  
> +	uclamp_cpu_get(rq, p);
>  	p->sched_class->enqueue_task(rq, p, flags);
>  }
>  
> @@ -1121,6 +1325,7 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
>  	if (!(flags & DEQUEUE_SAVE))
>  		sched_info_dequeued(rq, p);
>  
> +	uclamp_cpu_put(rq, p);
>  	p->sched_class->dequeue_task(rq, p, flags);
>  }

The ordering, is that right? We get while the task isn't enqueued yet,
which would suggest we put when the task is dequeued.