Commit f3a7e1a9 authored Oct 21, 2014 by Kirill Tkhai Committed by Ingo Molnar Oct 28, 2014

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.

2) dl_task_timer():
   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.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1413909356.19914.128.camel@tkhai


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent fcd964dd

kernel/sched/deadline.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -540,7 +540,7 @@ again:
		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);
		else
		resched_curr(rq);
		@@ -1626,8 +1626,12 @@ 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))
		if (check_resched) {
		if (dl_task(rq->curr))
		check_preempt_curr_dl(rq, p, 0);
		else
		resched_curr(rq);
		}
		}
		}

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