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

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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: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill Tkhai 2014-03-04 19:25:46 +04:00 committed by Ingo Molnar
parent a02ed5e3e0
commit 734ff2a71f
2 changed files with 15 additions and 2 deletions
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10
kernel/sched/deadline.c
View File

@ -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;

7
kernel/sched/rt.c
View File

@ -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;