First, we want to prevent placement of RT tasks on non-root rt_rqs which
we achieve in the task migration code that'd fall back to
root_task_group's rt_rq.
Second, we want to work with only root_task_group's rt_rq when iterating
all "real" rt_rqs when RT_GROUP is disabled. To achieve this we keep
root_task_group as the first one on the task_groups and break out
quickly.
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
---
kernel/sched/core.c | 2 +-
kernel/sched/rt.c | 9 ++++++---
kernel/sched/sched.h | 7 +++++++
3 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 47898f895a5a3..dfd2778622b8b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8958,7 +8958,7 @@ void sched_online_group(struct task_group *tg, struct task_group *parent)
unsigned long flags;
spin_lock_irqsave(&task_group_lock, flags);
- list_add_rcu(&tg->list, &task_groups);
+ list_add_tail_rcu(&tg->list, &task_groups);
/* Root should already exist: */
WARN_ON(!parent);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 41fed8865cb09..923ec978ff756 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -497,6 +497,9 @@ typedef struct task_group *rt_rq_iter_t;
static inline struct task_group *next_task_group(struct task_group *tg)
{
+ if (!rt_group_sched_enabled())
+ return NULL;
+
do {
tg = list_entry_rcu(tg->list.next,
typeof(struct task_group), list);
@@ -509,9 +512,9 @@ static inline struct task_group *next_task_group(struct task_group *tg)
}
#define for_each_rt_rq(rt_rq, iter, rq) \
- for (iter = container_of(&task_groups, typeof(*iter), list); \
- (iter = next_task_group(iter)) && \
- (rt_rq = iter->rt_rq[cpu_of(rq)]);)
+ for (iter = &root_task_group; \
+ iter && (rt_rq = iter->rt_rq[cpu_of(rq)]); \
+ iter = next_task_group(iter))
#define for_each_sched_rt_entity(rt_se) \
for (; rt_se; rt_se = rt_se->parent)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 1c457dc1472a3..d8d28c3d1ac5f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2148,6 +2148,13 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
#endif
#ifdef CONFIG_RT_GROUP_SCHED
+ /*
+ * p->rt.rt_rq is NULL initially and it is easier to assign
+ * root_task_group's rt_rq than switching in rt_rq_of_se()
+ * Clobbers tg(!)
+ */
+ if (!rt_group_sched_enabled())
+ tg = &root_task_group;
p->rt.rt_rq = tg->rt_rq[cpu];
p->rt.parent = tg->rt_se[cpu];
#endif
--
2.47.1
