Re: [PATCH v2 2/3] sched/dl: Cleanup prio_changed_dl()

Juri Lelli
2014-10-21T16:24:07Z

Hi Kirill,

On 02/10/14 10:52, Kirill Tkhai wrote:
> В Чт, 02/10/2014 в 11:36 +0200, Peter Zijlstra пишет:
>> On Wed, Oct 01, 2014 at 01:04:35AM +0400, Kirill Tkhai wrote:
>>> From: Kirill Tkhai <ktkhai@parallels.com>
>>>
>>> rq->curr task can't be in "dequeued" state in prio_changed_dl().
>>> (The only place we can have that is __schedule()). So, we delete
>>> rq->curr check.
>>
>> the CBS timer can throttle it right?
>
> Yeah, it's better to check for on_dl_rq():
>
> [PATCH]sched/dl: Cleanup prio_changed_dl()
>
> rq->curr task can't be in "dequeued" state in prio_changed_dl().
> (The only place we can have that is __schedule()). So, we delete
> rq->curr check.
>
> We shouldn't do balancing if deadline task is throttled too.
>
> Also delete "else" branch which is dead code (switched_to_dl()
> is not interested in dequeued tasks and we are not interested
> in balancing in this case).
>

So, I agree that calling switched_to_dl() makes little sense,
but don't we have to deal with updates to not running tasks as
in rt.c? Something like this maybe?

>From 75ee75a5fd76526baaed3ba8a58f3ff7daa89cd6 Mon Sep 17 00:00:00 2001
From: Juri Lelli <juri.lelli@arm.com>
Date: Tue, 21 Oct 2014 17:15:15 +0100
Subject: [PATCH] sched/deadline: cleanup prio_changed_dl()

---
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 28d6088..1e62e31 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1661,7 +1661,10 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
static void prio_changed_dl(struct rq *rq, struct task_struct *p,
int oldprio)
{
- if (task_on_rq_queued(p) || rq->curr == p) {
+ if (!on_dl_rq(&p->dl))
+ return;
+
+ if (rq->curr == p) {
#ifdef CONFIG_SMP
/*
* This might be too much, but unfortunately
@@ -1688,8 +1691,15 @@ static void prio_changed_dl(struct rq *rq, struct task_struct *p,
*/
resched_curr(rq);
#endif /* CONFIG_SMP */
- } else
- switched_to_dl(rq, p);
+ } else {
+ /*
+ * This task is not running, so if its deadline is
+ * now more imminent than that of the current running
+ * task then reschedule.
+ */
+ if (dl_time_before(p->dl.deadline, rq->curr->dl.deadline))
+ resched_curr(rq);
+ }
}

const struct sched_class dl_sched_class = {
--
2.1.0

Thanks,

- Juri

> Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 63f8b4a..ccea917 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1638,35 +1638,33 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
> static void prio_changed_dl(struct rq *rq, struct task_struct *p,
> int oldprio)
> {
> - if (task_on_rq_queued(p) || rq->curr == p) {
> + if (!on_dl_rq(&p->dl))
> + return;
> #ifdef CONFIG_SMP
> - /*
> - * This might be too much, but unfortunately
> - * we don't have the old deadline value, and
> - * we can't argue if the task is increasing
> - * or lowering its prio, so...
> - */
> - if (!rq->dl.overloaded)
> - pull_dl_task(rq);
> -
> - /*
> - * If we now have a earlier deadline task than p,
> - * then reschedule, provided p is still on this
> - * runqueue.
> - */
> - if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
> - rq->curr == p)
> - resched_curr(rq);
> -#else
> - /*
> - * Again, we don't know if p has a earlier
> - * or later deadline, so let's blindly set a
> - * (maybe not needed) rescheduling point.
> - */
> + /*
> + * This might be too much, but unfortunately
> + * we don't have the old deadline value, and
> + * we can't argue if the task is increasing
> + * or lowering its prio, so...
> + */
> + if (!rq->dl.overloaded)
> + pull_dl_task(rq);
> + /*
> + * If we now have a earlier deadline task than p,
> + * then reschedule, provided p is still on this
> + * runqueue.
> + */
> + if (dl_time_before(rq->dl.earliest_dl.curr, p->dl.deadline) &&
> + rq->curr == p)
> resched_curr(rq);
> +#else
> + /*
> + * Again, we don't know if p has a earlier
> + * or later deadline, so let's blindly set a
> + * (maybe not needed) rescheduling point.
> + */
> + resched_curr(rq);
> #endif /* CONFIG_SMP */
> - } else
> - switched_to_dl(rq, p);
> }
>
> const struct sched_class dl_sched_class = {
>
>
>