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>
---
kernel/sched.c | 3 +++
kernel/sched_rt.c | 43 ++++++++++++++++++++++++++++++++++++++-----
2 files changed, 41 insertions(+), 5 deletions(-)
Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -374,6 +374,8 @@ 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;
@@ -7116,6 +7118,7 @@ static void init_rt_rq(struct rt_rq *rt_
rt_rq->rt_throttled = 0;
#ifdef CONFIG_FAIR_GROUP_SCHED
+ rt_rq->rt_nr_boosted = 0;
rt_rq->rq = rq;
#endif
}
Index: linux-2.6/kernel/sched_rt.c
===================================================================
--- linux-2.6.orig/kernel/sched_rt.c
+++ linux-2.6/kernel/sched_rt.c
@@ -110,6 +110,23 @@ static void sched_rt_ratio_dequeue(struc
dequeue_rt_entity(rt_se);
}
+static inline int rt_rq_throttled(struct rt_rq *rt_rq)
+{
+ return rt_rq->rt_throttled && !rt_rq->rt_nr_boosted;
+}
+
+static int rt_se_boosted(struct sched_rt_entity *rt_se)
+{
+ struct rt_rq *rt_rq = group_rt_rq(rt_se);
+ struct task_struct *p;
+
+ if (rt_rq)
+ return !!rt_rq->rt_nr_boosted;
+
+ p = rt_task_of(rt_se);
+ return p->prio != p->normal_prio;
+}
+
#else
static inline unsigned int sched_rt_ratio(struct rt_rq *rt_rq)
@@ -149,6 +166,10 @@ static inline void sched_rt_ratio_dequeu
{
}
+static inline int rt_rq_throttled(struct rt_rq *rt_rq)
+{
+ return rt_rq->rt_throttled;
+}
#endif
static inline int rt_se_prio(struct sched_rt_entity *rt_se)
@@ -172,7 +193,7 @@ static int sched_rt_ratio_exceeded(struc
return 0;
if (rt_rq->rt_throttled)
- return 1;
+ return rt_rq_throttled(rt_rq);
period = (u64)sysctl_sched_rt_period * NSEC_PER_MSEC;
ratio = (period * rt_ratio) >> SCHED_RT_FRAC_SHIFT;
@@ -183,8 +204,10 @@ static int sched_rt_ratio_exceeded(struc
rq->rt_throttled = 1;
rt_rq->rt_throttled = 1;
- sched_rt_ratio_dequeue(rt_rq);
- return 1;
+ if (rt_rq_throttled(rt_rq)) {
+ sched_rt_ratio_dequeue(rt_rq);
+ return 1;
+ }
}
return 0;
@@ -265,6 +288,10 @@ void inc_rt_tasks(struct sched_rt_entity
update_rt_migration(rq_of_rt_rq(rt_rq));
#endif
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ if (rt_se_boosted(rt_se))
+ rt_rq->rt_nr_boosted++;
+#endif
}
static inline
@@ -295,6 +322,12 @@ void dec_rt_tasks(struct sched_rt_entity
update_rt_migration(rq_of_rt_rq(rt_rq));
#endif /* CONFIG_SMP */
+#ifdef CONFIG_FAIR_GROUP_SCHED
+ if (rt_se_boosted(rt_se))
+ rt_rq->rt_nr_boosted--;
+
+ WARN_ON(!rt_rq->rt_nr_running && rt_rq->rt_nr_boosted);
+#endif
}
static void enqueue_rt_entity(struct sched_rt_entity *rt_se)
@@ -303,7 +336,7 @@ static void enqueue_rt_entity(struct sch
struct rt_prio_array *array = &rt_rq->active;
struct rt_rq *group_rq = group_rt_rq(rt_se);
- if (group_rq && group_rq->rt_throttled)
+ if (group_rq && rt_rq_throttled(group_rq))
return;
list_add_tail(&rt_se->run_list, array->queue + rt_se_prio(rt_se));
@@ -496,7 +529,7 @@ static struct task_struct *pick_next_tas
if (unlikely(!rt_rq->rt_nr_running))
return NULL;
- if (sched_rt_ratio_exceeded(rt_rq))
+ if (rt_rq_throttled(rt_rq))
return NULL;
do {
--
--
