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    SubjectRe: [PATCH] sched/deadline: remove useless param from setup_new_dl_entity
    On 17/06/16 09:49, Steven Rostedt wrote:
    > On Fri, 17 Jun 2016 10:48:41 +0100
    > Juri Lelli <juri.lelli@arm.com> wrote:
    >
    > > setup_new_dl_entity() takes two parameters, but it only actually uses
    > > one of them to setup a new dl_entity.
    > >
    >
    > Actually this patch is making it so that setup_new_dl_entity() only
    > uses one of the parameters. Can you note why that change happened.
    > Because this change log implies that the second parameter wasn't used
    > before this patch, and that is incorrect.
    >

    True, but we were practically already using the same parameter, under a
    different name though, after

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

    as we currently do:

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

    > This patch reverts part of the change done in
    > commit 2d3d891d334 "sched/deadline: Add SCHED_DEADLINE inheritance
    > logic"
    >

    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. So, I guess the question
    is actually why we wanted to use pi_se's parameters (the potential PI
    donor) for setting up a new entity? Maybe we broke the situation where a
    task is currently boosted by a DEADLINE waiter and we swich the holder
    to DEADLINE?

    > It would be nice to have the reason in the change log.
    >

    Thanks a lot for pointing out what might be more than inaccuracy in the
    changelog.

    Best,

    - Juri

    >
    > > Remove the second, useless, parameter.
    > >
    > > 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>
    > > ---
    > > kernel/sched/deadline.c | 9 ++++-----
    > > 1 file changed, 4 insertions(+), 5 deletions(-)
    > >
    > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
    > > index fcb7f0217ff4..5229788a4765 100644
    > > --- a/kernel/sched/deadline.c
    > > +++ b/kernel/sched/deadline.c
    > > @@ -346,8 +346,7 @@ 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);
    > > @@ -367,8 +366,8 @@ 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;
    > > }
    > >
    > > /*
    > > @@ -1721,7 +1720,7 @@ 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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