linux-kernel - Re: [PATCH v4] sched/deadline: remove useless param from setup_new_dl

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Date:	Thu, 21 Jul 2016 15:46:14 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	xlpang@...hat.com
Cc:	peterz@...radead.org, rostedt@...dmis.org,
	linux-kernel@...r.kernel.org, mingo@...hat.com, luca.abeni@...tn.it
Subject: Re: [PATCH v4] sched/deadline: remove useless param from
 setup_new_dl_entity

On 21/07/16 15:36, Juri Lelli wrote:
> On 21/07/16 15:21, Juri Lelli wrote:
> > Hi,
> > 
> > On 18/07/16 21:37, Xunlei Pang wrote:
> > > On 2016/07/18 at 21:04, Juri Lelli wrote:
> > > > On 15/07/16 18:39, Xunlei Pang wrote:
> > > >> On 2016/07/13 at 18:58, Juri Lelli wrote:
> > > > [...]
> > > >
> > > >> Since this is only called for queued cases now, there is no need to
> > > >> check boosted stuff here. As enqueue_task(ENQUEUE_REPLENISH)
> > > >> is called before check_class_changed() in rt_mutex_setprio().
> > > >>
> > > > But we don't do the same in setscheduler, right?
> > > 
> > > If p is deadline PI-boosted, setscheduler() won't call change its sched_class.
> > > If p isn't deadline PI-boosted, then pi_task is NULL.
> > > 
> > > So, I think the added code won't hit. Did I miss something?
> > > 
> > 
> > No, I think you are right.
> > 
> 
> Oh, and we need to filter the call after rt_mutex_setprio has
> already issued a replenishment.
> 

Does something like this on top of v4 make sense?

---
 kernel/sched/deadline.c | 22 +++++++---------------
 1 file changed, 7 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index dc56f5be0112..6f05ac78711c 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -350,9 +350,8 @@ 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);
-	struct task_struct *pi_task;
-	struct sched_dl_entity *pi_se = dl_se;
 
+	WARN_ON(dl_se->dl_boosted);
 	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
 
 	/*
@@ -364,21 +363,12 @@ static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
 		return;
 
 	/*
-	 * Use the scheduling parameters of the top pi-waiter task,
-	 * if we have one from which we can inherit a deadline.
-	 */
-	if (dl_se->dl_boosted &&
-	    (pi_task = rt_mutex_get_top_task(dl_task_of(dl_se))) &&
-	    dl_prio(pi_task->normal_prio))
-		pi_se = &pi_task->dl;
-
-	/*
 	 * We use the regular wall clock time to set deadlines in the
 	 * 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;
 }
 
 /*
@@ -1734,9 +1724,11 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
 	if (task_on_rq_queued(p)) {
 		/*
 		 * If p is not queued we will update its parameters at next
-		 * wakeup.
+		 * wakeup. If p is dl_boosted we already updated its params in
+		 * rt_mutex_setprio()->enqueue_task(..., ENQUEUE_REPLENISH).
 		 */
-		if (dl_time_before(p->dl.deadline, rq_clock(rq)))
+		if (dl_time_before(p->dl.deadline, rq_clock(rq)) &&
+				!p->dl.dl_boosted)
 			setup_new_dl_entity(&p->dl);
 
 		if (rq->curr != p) {
--