Messages in this thread Patch in this message | | | Subject | Re: [PATCH] sched_rt_rq_enqueue() resched idle | From | Peter Zijlstra <> | Date | Wed, 27 Aug 2008 15:19:03 +0200 |
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Ingo, please apply.
--- Subject: sched: sched_rt_rq_enqueue() resched idle From: John Blackwood <john.blackwood@ccur.com> Date: Tue, 26 Aug 2008 15:09:43 -0400
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> --- kernel/sched_rt.c | 2 ++ 1 file changed, 2 insertions(+)
Index: linux-2.6/kernel/sched_rt.c =================================================================== --- linux-2.6.orig/kernel/sched_rt.c +++ linux-2.6/kernel/sched_rt.c @@ -199,6 +199,8 @@ static inline struct rt_rq *group_rt_rq( 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)
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