From f3ade837808121ff8bab9c56725f4fe40ec85a56 Mon Sep 17 00:00:00 2001 From: John Blackwood Date: Tue, 26 Aug 2008 15:09:43 -0400 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- kernel/sched_rt.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 998ba54b45..07d9b33079 100644 --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -199,6 +199,8 @@ static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se) 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) -- 2.39.5