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Subject[PATCH v3] sched/deadline: remove useless param from setup_new_dl_entity
Date
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 <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Luca Abeni <luca.abeni@unitn.it>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>

---
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 | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fcb7f0217ff4..7aeb21963d3c 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;
+ struct sched_dl_entity *pi_se = dl_se;

WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));

@@ -363,6 +364,15 @@ 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.).
@@ -1721,7 +1731,7 @@ 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
--
2.7.4
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