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Commit 734ff2a7 authored by Kirill Tkhai's avatar Kirill Tkhai Committed by Ingo Molnar
Browse files

sched/rt: Fix picking RT and DL tasks from empty queue 



The problems:

1) We check for rt_nr_running before call of put_prev_task().
   If previous task is RT, its rt_rq may become throttled
   and dequeued after this call.

In case of p is from rt->rq this just causes picking a task
from throttled queue, but in case of its rt_rq is child
we are guaranteed catch BUG_ON.

2) The same with deadline class. The only difference we operate
   on only dl_rq.

This patch fixes all the above problems and it adds a small skip in the
DL update like we've already done for RT class:

	if (unlikely((s64)delta_exec <= 0))
		return;

This will optimize sequential update_curr_dl() calls a little.

Signed-off-by: default avatarKirill Tkhai <ktkhai@parallels.com>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@gmail.com>
Link: http://lkml.kernel.org/r/1393946746.3643.3.camel@tkhai


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent a02ed5e3

kernel/sched/deadline.c

+8 −2
Original line number Diff line number Diff line
@@ -609,8 +609,8 @@ static void update_curr_dl(struct rq *rq) 
	 * approach need further study.

	 */

	delta_exec = rq_clock_task(rq) - curr->se.exec_start;

	if (unlikely((s64)delta_exec < 0))

		delta_exec = 0;

	if (unlikely((s64)delta_exec <= 0))

		return;



	schedstat_set(curr->se.statistics.exec_max,

		      max(curr->se.statistics.exec_max, delta_exec));
@@ -1023,6 +1023,12 @@ struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev) 


	if (need_pull_dl_task(rq, prev))

		pull_dl_task(rq);

	/*

	 * When prev is DL, we may throttle it in put_prev_task().

	 * So, we update time before we check for dl_nr_running.

	 */

	if (prev->sched_class == &dl_sched_class)

		update_curr_dl(rq);



	if (unlikely(!dl_rq->dl_nr_running))

		return NULL;

kernel/sched/rt.c

+7 −0
Original line number Diff line number Diff line
@@ -1379,6 +1379,13 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev) 
			return RETRY_TASK;

	}



	/*

	 * We may dequeue prev's rt_rq in put_prev_task().

	 * So, we update time before rt_nr_running check.

	 */

	if (prev->sched_class == &rt_sched_class)

		update_curr_rt(rq);



	if (!rt_rq->rt_nr_running)

		return NULL;