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SubjectRe: [PATCH v2] sched/deadline: remove useless param from setup_new_dl_entity
On Tue, 5 Jul 2016 10:20:13 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Wed, 29 Jun 2016 20:07:43 +0100
> Juri Lelli <juri.lelli@arm.com> wrote:
>
>
> > ---
> > 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;
> > +
>
> OK, I'm micro-optimizing now, but hey, isn't this a fast path?
>
> What about changing the above to:
>
> struct task_struct *pi_task;
> [...]
>
> if (dl_se->dl_boosted && dl_prio(pi_task->normal_prio &&
> (pi_task = rt_mutex_get_top_task(dl_task_of(dl_se)))
> pe_se = &pi_task->dl;
>
> This way we don't need to do any work of looking at
> rt_mutex_get_top_task() for the normal case.

If something like this is done, I think that enqueue_task_dl() (that
contains similar code) should be updated too.


Thanks,
Luca

>
> -- Steve
>
>
> > + /*
> > * 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
>

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