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 10:03:37 +0200 |
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On Tue, 2008-08-26 at 15:09 -0400, John Blackwood wrote: > Hi Peter, > > 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.
Very good spotting, Thanks!
However I think the patch isn't quite good, as highest_prio is only available on SMP || RT_GROUP_SCHED. Furthermore, on !RT_GROUP_SCHED any RT task will be higher than current, so we can do the below, do you agree?
--- diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c index 94daace..f672aee 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)
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