Hi all,
trying to debug a reclaiming issue discovered by Daniel, I find myself
confused by the push logic... Maybe I am misunderstanding something
very obvious, so I ask here:
- push_dl_task() selects a task to be pushed, and then searches for a
runqueue to push the task to by calling find_lock_later_rq()
- if I understand well, find_lock_later_rq() checks all the candidate
runqueues for pushing, and then compares the deadline of the task
with "dl.earliest_dl.curr" of the candidate runqueue, to check if
pushing the task there makes sense or not
- now, my understanding is that in order to implement gEDF task T must
be pushed on CPU C if the deadline of T is smaller than the earliest
deadline of tasks on C... That is to say, the deadline of T must be
smaller than the deadline of the task that is currently executing on
C... No?
- But as far as I understand "dl.earliest_dl.curr" is the earliest
deadline of _pushable_ tasks that are on the remote runqueue... That
is to say, "earliest_dl.curr" does not consider the deadline of the
task currently executing on the remote runqueue
- So, it seems to me that tasks are sometimes pushed to other runqueues
even if they have a deadline that is not smaller than the deadline of
the task executing on the "target" runqueue (so, a task is pushed but
not immediately scheduled for execution). Is this correct? What is
the logic behind this behaviour?
I would be tempted to say that the correct check is not
dl_time_before(task->dl.deadline, later_rq->dl.earliest_dl.curr)
(as it is now in find_lock_later_rq()), but
dl_time_before(task->dl.deadline, later_rq->curr->dl.deadline)
This, in my view, would migrate a task only when it is going to preempt
the current of the remote runqueue. What am I missing?
Thanks,
Luca
