On 2016/07/13 at 18:58, Juri Lelli wrote:
> 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 <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Steven Rostedt <[email protected]>
> Cc: Luca Abeni <[email protected]>
> Cc: Xunlei Pang <[email protected]>
> Signed-off-by: Juri Lelli <[email protected]>
>
> ---
> 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;
Since this is only called for queued cases now, there is no need to
check boosted stuff here. As enqueue_task(ENQUEUE_REPLENISH)
is called before check_class_changed() in rt_mutex_setprio().
Regards,
Xunlei
> +
> + /*
> * 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
> + }
> }
> }
>
