Re: [PATCH v5] sched/deadline: fix earliest_dl.next logic

[Luca Abeni]

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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