sched: rt-group: deal with PI

Steven mentioned the fun case where a lock holding task will be throttled.

Simple fix: allow groups that have boosted tasks to run anyway.

If a runnable task in a throttled group gets boosted the dequeue/enqueue
done by rt_mutex_setprio() is enough to unthrottle the group.

This is ofcourse not quite correct. Two possible ways forward are:
  - second prio array for boosted tasks
  - boost to a prio ceiling (this would also work for deadline scheduling)

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 3 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 88a17c7128c3..cecaea67ae9b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -362,6 +362,8 @@ struct rt_rq {
         u64 rt_time;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
+        unsigned long rt_nr_boosted;
+
         struct rq *rq;
         struct list_head leaf_rt_rq_list;
         struct task_group *tg;
@@ -7112,6 +7114,7 @@ static void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq)
         rt_rq->rt_throttled = 0;
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
+        rt_rq->rt_nr_boosted = 0;
         rt_rq->rq = rq;
 #endif
 }