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sched/rt: Migrate equal priority tasks to available CPUs

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commit 3be209a8e2 upstream.

Commit 43fa5460fe ("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>
Link: http://lkml.kernel.org/r/1315837684-18733-1-git-send-email-sbohrer@rgmadvisors.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Shawn Bohrer 2011-09-12 09:28:04 -05:00 committed by Greg Kroah-Hartman
parent ca64baea4d
commit 113f8b8f99
1 changed files with 2 additions and 2 deletions
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4
kernel/sched_rt.c
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@ -1038,7 +1038,7 @@ 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);
@ -1569,7 +1569,7 @@ 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);
}