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Subject[RFC] sched/dl: Fix preemption checks

1)switched_to_dl() check is wrong. We reschedule only
if rq->curr is deadline task, and we do not reschedule
if it's a lower priority task. But we must always
preempt a task of other classes.

Policy does not change in case of priority inheritance.
rt_mutex_setprio() changes prio, while policy remains old.

So we lose some balancing logic in dl_task_timer() and
switched_to_dl() when we check policy instead of priority.
Boosted task may be rq->curr.

(I didn't change switched_from_dl() because no check is
necessary there at all).

I've looked at this place(switched_to_dl) several times
and even fixed this function, but found just now...
I suppose some performance tests may work better after this.

Completely untested, just RFC.

Juri how about this?

Signed-off-by: Kirill Tkhai <>
kernel/sched/deadline.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 256e577..937a875 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -532,7 +532,7 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
dl_se->dl_yielded = 0;
if (task_on_rq_queued(p)) {
enqueue_task_dl(rq, p, ENQUEUE_REPLENISH);
- if (task_has_dl_policy(rq->curr))
+ if (dl_task(rq->curr))
check_preempt_curr_dl(rq, p, 0);
@@ -1607,8 +1607,12 @@ static void switched_to_dl(struct rq *rq, struct task_struct *p)
/* Only reschedule if pushing failed */
check_resched = 0;
#endif /* CONFIG_SMP */
- if (check_resched && task_has_dl_policy(rq->curr))
- check_preempt_curr_dl(rq, p, 0);
+ if (check_resched) {
+ if (dl_task(rq->curr))
+ check_preempt_curr_dl(rq, p, 0);
+ else
+ resched_curr(rq);
+ }

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