linux-kernel - Re: [PATCH] sched/deadline: remove useless param from setup_new_dl

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Date:	Fri, 17 Jun 2016 22:15:18 +0200
From:	luca abeni <luca.abeni@...tn.it>
To:	Juri Lelli <juri.lelli@....com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, mingo@...hat.com
Subject: Re: [PATCH] sched/deadline: remove useless param from
 setup_new_dl_entity

On Fri, 17 Jun 2016 17:28:37 +0100
Juri Lelli <juri.lelli@....com> wrote:
[...]
> True, but we were practically already using the same parameter, under a
> different name though, after
> 
> 2f9f3fdc928 "sched/deadline: Remove dl_new from struct sched_dl_entity"
> 
> as we currently do:
> 
>   setup_new_dl_entity(&p->dl, &p->dl)
> 
> > This patch reverts part of the change done in
> > commit 2d3d891d334 "sched/deadline: Add SCHED_DEADLINE inheritance
> > logic"
> >   
> 
> Before Luca's change we were doing
> 
>  setup_new_dl_entity(dl_se, pi_se)
> 
> in update_dl_entity() for a dl_se->new entity. So, I guess the question
> is actually why we wanted to use pi_se's parameters (the potential PI
> donor) for setting up a new entity?
That's a good question :)

> Maybe we broke the situation where a
> task is currently boosted by a DEADLINE waiter and we swich the holder
> to DEADLINE?
I remember I tested this setup (using linaro's version of rt-app), and
it seemed to work correctly...

Re-reading the code now, I actually wonder why my patch did not break
inheritance in this situation...


			Luca
> 
> > It would be nice to have the reason in the change log.
> >   
> 
> Thanks a lot for pointing out what might be more than inaccuracy in the
> changelog.
> 
> Best,
> 
> - Juri
> 
> >   
> > > Remove the second, useless, parameter.
> > > 
> > > Cc: Ingo Molnar <mingo@...hat.com>
> > > Cc: Peter Zijlstra <peterz@...radead.org>
> > > Cc: Steven Rostedt <rostedt@...dmis.org>
> > > Cc: Luca Abeni <luca.abeni@...tn.it>
> > > Signed-off-by: Juri Lelli <juri.lelli@....com>
> > > ---
> > >  kernel/sched/deadline.c | 9 ++++-----
> > >  1 file changed, 4 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > > index fcb7f0217ff4..5229788a4765 100644
> > > --- a/kernel/sched/deadline.c
> > > +++ b/kernel/sched/deadline.c
> > > @@ -346,8 +346,7 @@ static void check_preempt_curr_dl(struct rq *rq, struct task_struct *p,
> > >   * one, and to (try to!) reconcile itself with its own scheduling
> > >   * parameters.
> > >   */
> > > -static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se,
> > > -				       struct sched_dl_entity *pi_se)
> > > +static inline void setup_new_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);
> > > @@ -367,8 +366,8 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se,
> > >  	 * future; in fact, we must consider execution overheads (time
> > >  	 * spent on hardirq context, etc.).
> > >  	 */
> > > -	dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> > > -	dl_se->runtime = pi_se->dl_runtime;
> > > +	dl_se->deadline = rq_clock(rq) + dl_se->dl_deadline;
> > > +	dl_se->runtime = dl_se->dl_runtime;
> > >  }
> > >  
> > >  /*
> > > @@ -1721,7 +1720,7 @@ static void switched_from_dl(struct rq *rq, struct task_struct *p)
> > >  static void switched_to_dl(struct rq *rq, struct task_struct *p)
> > >  {
> > >  	if (dl_time_before(p->dl.deadline, rq_clock(rq)))
> > > -		setup_new_dl_entity(&p->dl, &p->dl);
> > > +		setup_new_dl_entity(&p->dl);
> > >  
> > >  	if (task_on_rq_queued(p) && rq->curr != p) {
> > >  #ifdef CONFIG_SMP  
> >