[PATCH v4] sched/deadline: remove useless param from setup_new_dl_entity

From: Juri Lelli
Date: Wed Jul 13 2016 - 06:58:32 EST


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.

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.

Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Luca Abeni <luca.abeni@xxxxxxxx>
Cc: Xunlei Pang <xpang@xxxxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxx>

---
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 | 39 ++++++++++++++++++++++++++++-----------
1 file changed, 28 insertions(+), 11 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index fcb7f0217ff4..dc56f5be0112 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.).
@@ -1720,19 +1730,26 @@ 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);

- if (task_on_rq_queued(p) && rq->curr != p) {
+ if (task_on_rq_queued(p)) {
+ /*
+ * If p is not queued we will update its parameters at next
+ * wakeup.
+ */
+ if (dl_time_before(p->dl.deadline, rq_clock(rq)))
+ setup_new_dl_entity(&p->dl);
+
+ if (rq->curr != p) {
#ifdef CONFIG_SMP
- if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
- queue_push_tasks(rq);
+ if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded)
+ queue_push_tasks(rq);
#else
- if (dl_task(rq->curr))
- check_preempt_curr_dl(rq, p, 0);
- else
- resched_curr(rq);
+ if (dl_task(rq->curr))
+ check_preempt_curr_dl(rq, p, 0);
+ else
+ resched_curr(rq);
#endif
+ }
}
}

--
2.7.4