[PATCH v2] sched/deadline: remove useless param from setup_new_dl_entity

[Juri Lelli]

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.

Restore this behaviour (as we want to correctly initialize parameters of
a boosted task that enters DEADLINE) by removing the useless second
parameter of setup_new_dl_entity() and retrieving the top waiter
directly from inside that function.

Cc: Ingo Molnar <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Luca Abeni <luca.ab...@unitn.it>
Signed-off-by: Juri Lelli <juri.le...@arm.com>

---
 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 | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fcb7f0217ff4..2000ad2294d5 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -346,11 +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);
+       struct task_struct *pi_task = rt_mutex_get_top_task(dl_task_of(dl_se));
+       struct sched_dl_entity *pi_se = dl_se;
 
        WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
 
@@ -363,6 +364,13 @@ 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 (pi_task && dl_se->dl_boosted && 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.).
@@ -1721,7 +1729,7 @@ 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
-- 
2.7.0