linux-kernel - Re: [RFC v3 1/6] Track the active utilisation

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Date:   Fri, 18 Nov 2016 14:55:54 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luca Abeni <luca.abeni@...tn.it>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@....com>,
        Claudio Scordino <claudio@...dence.eu.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC v3 1/6] Track the active utilisation

On Mon, Oct 24, 2016 at 04:06:33PM +0200, Luca Abeni wrote:

> @@ -498,6 +514,8 @@ static void update_dl_entity(struct sched_dl_entity *dl_se,
>  	struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
>  	struct rq *rq = rq_of_dl_rq(dl_rq);
>  
> +	add_running_bw(dl_se, dl_rq);
> +
>  	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
>  	    dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
>  		dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> @@ -947,14 +965,19 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
>  		return;
>  	}
>  
> +	if (p->on_rq == TASK_ON_RQ_MIGRATING)
> +		add_running_bw(&p->dl, &rq->dl);
> +
>  	/*
>  	 * If p is throttled, we do nothing. In fact, if it exhausted
>  	 * its budget it needs a replenishment and, since it now is on
>  	 * its rq, the bandwidth timer callback (which clearly has not
>  	 * run yet) will take care of this.
>  	 */
> -	if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH))
> +	if (p->dl.dl_throttled && !(flags & ENQUEUE_REPLENISH)) {
> +		add_running_bw(&p->dl, &rq->dl);
>  		return;
> +	}
>  
>  	enqueue_dl_entity(&p->dl, pi_se, flags);
>  

I realize the enqueue path is a bit of a maze, but this hurts my head.

Isn't there anything we can do to streamline this a bit?

Maybe move the add_running_bw() from update_dl_entity() to the
ENQUEUE_WAKEUP branch in enqueue_dl_entity()? Because that's what you
really want, isn't it? Its not actually related to recomputing the
absolute deadline.

> @@ -972,6 +995,12 @@ static void dequeue_task_dl(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	update_curr_dl(rq);
>  	__dequeue_task_dl(rq, p, flags);
> +
> +	if (p->on_rq == TASK_ON_RQ_MIGRATING)
> +		sub_running_bw(&p->dl, &rq->dl);
> +
> +	if (flags & DEQUEUE_SLEEP)
> +		sub_running_bw(&p->dl, &rq->dl);
>  }

We could look at adding more enqueue/dequeue flags to streamline this a
bit, bit lets not do that now.