sched/rt: Fix picking RT and DL tasks from empty queue (734ff2a7) · Commits · 戴 / test

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>

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;

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