On Thu, Feb 23, 2017 at 03:14:59PM +0900, Byungchul Park wrote:
> Let's consider the following example.
>
> timeline : o...................o.........o.......o..o
> ^ ^ ^ ^ ^
> | | | | |
> start | | | |
> original runtime | | |
> sleep with (-)runtime | |
> original deadline |
> wake up
>
> When this task is woken up, a negative runtime should be considered,
> which means that the task should get penalized when assigning runtime,
> becasue it already spent more than expected. Current code handles this
> by replenishing a runtime in hrtimer callback for deadline. But this
> approach has room for improvement:
>
> It will be replenished twice unnecessarily if the task sleeps for
> long time so that the deadline, assigned in the hrtimer callback,
> also passed. In other words, one happens in the callback and the
> other happens in update_dl_entiry() when waking it up.
>
> So force to replenish it for sleep tasks when waking it up.
To be honest, I think this patch is more valuable when used with
removing unnecessary hrtimer interrupt for deadline control, but
not that much without it.
I just wonder what you think.
>
> Signed-off-by: Byungchul Park <byungchul.p...@lge.com>
> ---
> kernel/sched/deadline.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 27737f3..cb43ce9 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -498,8 +498,9 @@ static void update_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);
>
> - if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
> - dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
> + if (dl_time_before(dl_se->deadline, rq_clock(rq)))
> + replenish_dl_entity(dl_se, pi_se);
> + else if (dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
> dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
> dl_se->runtime = pi_se->dl_runtime;
> }
> @@ -621,13 +622,11 @@ static enum hrtimer_restart dl_task_timer(struct
> hrtimer *timer)
> * __dequeue_task_dl()
> * prev->on_rq = 0;
> *
> - * We can be both throttled and !queued. Replenish the counter
> - * but do not enqueue -- wait for our wakeup to do that.
> + * We can be both throttled and !queued. Wait for our wakeup to
> + * replenish runtime and enqueue p.
> */
> - if (!task_on_rq_queued(p)) {
> - replenish_dl_entity(dl_se, dl_se);
> + if (!task_on_rq_queued(p))
> goto unlock;
> - }
>
> #ifdef CONFIG_SMP
> if (unlikely(!rq->online)) {
> --
> 1.9.1
