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

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Date:   Fri, 18 Nov 2016 16:06:10 +0100
From:   luca abeni <luca.abeni@...tn.it>
To:     Peter Zijlstra <peterz@...radead.org>
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

Hi Peter,

On Fri, 18 Nov 2016 14:55:54 +0100
Peter Zijlstra <peterz@...radead.org> wrote:

> 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.

Right... I'll change the code in this way. I am currently modifying
this code (because after Juri's review I realized that there is an
issue - see last email exchange with Juri); I'll make this change as
soon as the code stabilizes.


		Thanks,
			Luca