sched: fix sched_rt_rq_enqueue() resched idle
When sysctl_sched_rt_runtime is set to something other than -1 and the
CONFIG_RT_GROUP_SCHED kernel parameter is NOT enabled, we get into a state
where we see one or more CPUs idling forvever even though there are
real-time
tasks in their rt runqueue that are able to run (no longer throttled).
The sequence is:
- A real-time task is running when the timer sets the rt runqueue
to throttled, and the rt task is resched_task()ed and switched
out, and idle is switched in since there are no non-rt tasks to
run on that cpu.
- Eventually the do_sched_rt_period_timer() runs and un-throttles
the rt runqueue, but we just exit the timer interrupt and go back
to executing the idle task in the idle loop forever.
If we change the sched_rt_rq_enqueue() routine to use some of the code
from the CONFIG_RT_GROUP_SCHED enabled version of this same routine and
resched_task() the currently executing task (idle in our case) if it is
a lower priority task than the higher rt task in the now un-throttled
runqueue, the problem is no longer observed.
Signed-off-by: John Blackwood <john.blackwood@ccur.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 998ba54b..07d9b33 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -199,6 +199,8 @@
static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
{
+ if (rt_rq->rt_nr_running)
+ resched_task(rq_of_rt_rq(rt_rq)->curr);
}
static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq)
