On Tue, 28 Feb 2017 11:07:54 +0100
Daniel Bristot de Oliveira <[email protected]> wrote:
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 3c94d85..3a88def 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -694,6 +694,37 @@ void init_dl_task_timer(struct sched_dl_entity *dl_se)
> timer->function = dl_task_timer;
> }
>
> +/*
> + * During the activation, CBS checks if it can reuse the current task's
> + * runtime and period. If the deadline of the task is in the past, CBS
> + * cannot use the runtime, and so it replenishes the task. This rule
> + * works fine for implicit deadline tasks (deadline == period), and the
> + * CBS was designed for implicit deadline tasks. However, a task with
> + * constrained deadline (deadine < period) might be awakened after the
> + * deadline, but before the next period. In this case, replenishing the
> + * task would allow it to run for runtime / deadline. As in this case
> + * deadline < period, CBS enables a task to run for more than the
> + * runtime / period. In a very load system, this can cause the domino
In a very loaded system, this can cause a domino
> + * effect, making other tasks to miss their deadlines.
effect, making other tasks miss their deadlines.
> + *
> + * To avoid this problem, in the activation of a constrained deadline
> + * task after the deadline but before the next period, throttle the
> + * task and set the replenishing timer to the begin of the next period,
to the beginning of the next
> + * unless it is boosted.
> + */
> +static inline void dl_check_constrained_dl(struct sched_dl_entity *dl_se)
> +{
> + struct task_struct *p = dl_task_of(dl_se);
> + struct rq *rq = rq_of_dl_rq(dl_rq_of_se(dl_se));
> +
> + if (dl_time_before(dl_se->deadline, rq_clock(rq)) &&
> + dl_time_before(rq_clock(rq), dl_next_period(dl_se))) {
> + if (unlikely(dl_se->dl_boosted || !start_dl_timer(p)))
> + return;
> + dl_se->dl_throttled = 1;
> + }
> +}
> +
> static
> int dl_runtime_exceeded(struct sched_dl_entity *dl_se)
> {
> @@ -927,6 +958,11 @@ static void dequeue_dl_entity(struct sched_dl_entity
> *dl_se)
> __dequeue_dl_entity(dl_se);
> }
>
> +static inline bool dl_is_constrained(struct sched_dl_entity *dl_se)
> +{
> + return dl_se->dl_deadline < dl_se->dl_period;
> +}
> +
> static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
> {
> struct task_struct *pi_task = rt_mutex_get_top_task(p);
> @@ -953,6 +989,15 @@ static void enqueue_task_dl(struct rq *rq, struct
> task_struct *p, int flags)
> }
>
> /*
> + * Check if a constrained deadline task was activated
> + * after the deadline but before the next period.
> + * If that is the case, the task will be throttled and
> + * the replenishment timer will be set to the next period.
> + */
> + if (!pi_se->dl_throttled && dl_is_constrained(pi_se))
> + dl_check_constrained_dl(pi_se);
> +
> + /*
> * If p is throttled, we do nothing. In fact, if it exhausted
> * its budget it needs a replenishment and, since it now is on
> * its rq, the bandwidth timer callback (which clearly has not
Except for the grammar mistakes...
Reviewed-by: Steven Rostedt (VMware) <[email protected]>
-- Steve
