linux-kernel - [PATCH v6] sched/deadline: remove useless param from setup_new_dl

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Message-Id: <1470409675-20935-1-git-send-email-juri.lelli@arm.com>
Date:	Fri,  5 Aug 2016 16:07:55 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	peterz@...radead.org
Cc:	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	mingo@...hat.com, luca.abeni@...tn.it, juri.lelli@....com,
	xpang@...hat.com
Subject: [PATCH v6] sched/deadline: remove useless param from setup_new_dl_entity

setup_new_dl_entity() takes two parameters, but it only actually uses
one of them, under a different name, to setup a new dl_entity, after:

 2f9f3fdc928 "sched/deadline: Remove dl_new from struct sched_dl_entity"

as we currently do

 setup_new_dl_entity(&p->dl, &p->dl)

However, 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: we were using pi_se's
parameters (the potential PI donor) for setting up a new entity.

This change removes the useless second parameter of setup_new_dl_entity().
While we are at it we also optimize things further calling setup_new_dl_
entity() only for already queued tasks, since (as pointed out by Xunlei)
we already do the very same update at tasks wakeup time anyway. By doing
so, we don't need to worry about a potential PI donor anymore, as rt_
mutex_setprio() takes care of that already for us.

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>
Cc: Xunlei Pang <xpang@...hat.com>
Signed-off-by: Juri Lelli <juri.lelli@....com>
Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

---
 Changes from v5:
   - simply return if task is not enqueued; improves readability and
     reduces indentation

 Changes from v4:
   - remove dead code checking for boosted status, as never triggered
     after rt_mutex_setprio()

 Changes from v3:
   - call setup_new_dl_entity only if task is enqueued already

 Changes from v2:
   - optimize by calling rt_mutex_get_top_task only if the task is
     boosted (as suggested by Steve)

 Changes from v1:
   - Steve pointed out that we were actually using the second parameter
     to permorm initialization
   - Luca confirmed that behavior is slightly changed w.r.t. before his
     change
   - changelog updated and original behavior restored
---
 kernel/sched/deadline.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fcb7f0217ff4..03f35f66cf1f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -346,12 +346,12 @@ 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);
 
+	WARN_ON(dl_se->dl_boosted);
 	WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
 
 	/*
@@ -367,8 +367,8 @@ 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;
 }
 
 /*
@@ -1720,10 +1720,20 @@ 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 p is not queued we will update its parameters at next wakeup. */
+	if (!task_on_rq_queued(p))
+		return;
+
+	/*
+	 * If p is boosted we already updated its params in
+	 * rt_mutex_setprio()->enqueue_task(..., ENQUEUE_REPLENISH),
+	 * p's deadline being now already after rq_clock(rq).
+	 */
 	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) {
+	if (rq->curr != p) {
 #ifdef CONFIG_SMP
 		if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
 			queue_push_tasks(rq);
-- 
2.7.0