Commit 3be209a8 authored Sep 12, 2011 by Shawn Bohrer Committed by Ingo Molnar Sep 18, 2011

sched/rt: Migrate equal priority tasks to available CPUs



Commit 43fa5460 ("sched: Try not to
migrate higher priority RT tasks") also introduced a change in behavior
which keeps RT tasks on the same CPU if there is an equal priority RT
task currently running even if there are empty CPUs available.

This can cause unnecessary wakeup latencies, and can prevent the
scheduler from balancing all RT tasks across available CPUs.

This change causes an RT task to search for a new CPU if an equal
priority RT task is already running on wakeup.  Lower priority tasks
will still have to wait on higher priority tasks, but the system should
still balance out because there is always the possibility that if there
are both a high and low priority RT tasks on a given CPU that the high
priority task could wakeup while the low priority task is running and
force it to search for a better runqueue.

Signed-off-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: stable@kernel.org # 37+
Link: http://lkml.kernel.org/r/1315837684-18733-1-git-send-email-sbohrer@rgmadvisors.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 003f6c9d

kernel/sched_rt.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1050,7 +1050,7 @@ select_task_rq_rt(struct task_struct *p, int sd_flag, int flags)
		*/
		if (curr && unlikely(rt_task(curr)) &&
		(curr->rt.nr_cpus_allowed < 2 \|\|
		curr->prio < p->prio) &&
		curr->prio <= p->prio) &&
		(p->rt.nr_cpus_allowed > 1)) {
		int target = find_lowest_rq(p);

		@@ -1581,7 +1581,7 @@ static void task_woken_rt(struct rq rq, struct task_struct p)
		p->rt.nr_cpus_allowed > 1 &&
		rt_task(rq->curr) &&
		(rq->curr->rt.nr_cpus_allowed < 2 \|\|
		rq->curr->prio < p->prio))
		rq->curr->prio <= p->prio))
		push_rt_tasks(rq);
		}

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