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SubjectRe: [PATCH v5] sched/deadline: fix earliest_dl.next logic
From
Date
Hi,

On 12/02/2015 02:33 PM, Wanpeng Li wrote:
[...]
>> We updated leftmost above, can't we simply use that path for this thing
>> below?
>
> Do you mean something like below?
>
> @@ -195,6 +195,9 @@ static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
>
> next_node = rb_next(&p->pushable_dl_tasks);
> dl_rq->pushable_dl_tasks_leftmost = next_node;
> + if (has_pushable_dl_tasks(rq))
I do not know the rb trees code, but... Are you sre you can call has_pushable_tasks() here?
(I suspect pushable_dl_tasks_root is not updated yet, so maybe has_pushable_dl_tasks() risks
to return a wrong value?)

> + dl_rq->earliest_dl.next = rb_entry(rq->dl.pushable_dl_tasks_leftmost,
> + struct task_struct, pushable_dl_task)->dl.deadline;
I am not sure if this is what Juri meant, but maybe something like this?

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 087d090..26d3279 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -185,11 +185,6 @@ static void enqueue_pushable_dl_task(struct rq *rq, struct task_struct *p)
rb_insert_color(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
}

-static inline int has_pushable_dl_tasks(struct rq *rq)
-{
- return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root);
-}
-
static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)
{
struct dl_rq *dl_rq = &rq->dl;
@@ -202,16 +197,18 @@ static void dequeue_pushable_dl_task(struct rq *rq, struct task_struct *p)

next_node = rb_next(&p->pushable_dl_tasks);
dl_rq->pushable_dl_tasks_leftmost = next_node;
+ if (next_node)
+ dl_rq->earliest_dl.next = rb_entry(next_node,
+ struct task_struct, pushable_dl_tasks)->dl.deadline;
}

rb_erase(&p->pushable_dl_tasks, &dl_rq->pushable_dl_tasks_root);
RB_CLEAR_NODE(&p->pushable_dl_tasks);
+}

- if (has_pushable_dl_tasks(rq)) {
- p = rb_entry(rq->dl.pushable_dl_tasks_leftmost,
- struct task_struct, pushable_dl_tasks);
- dl_rq->earliest_dl.next = p->dl.deadline;
- }
+static inline int has_pushable_dl_tasks(struct rq *rq)
+{
+ return !RB_EMPTY_ROOT(&rq->dl.pushable_dl_tasks_root);
}

static int push_dl_task(struct rq *rq);

I do not know if it is correct, but I ran some quick tests and seem to work
without problems.



Luca


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