Commit 61d3164f authored by Michal Koutný's avatar Michal Koutný Committed by Peter Zijlstra
Browse files

sched: Skip non-root task_groups with disabled RT_GROUP_SCHED 



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: default avatarMichal Koutný <mkoutny@suse.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250310170442.504716-6-mkoutny@suse.com
parent e34e0131

kernel/sched/core.c

+1 −1
Original line number Diff line number Diff line
@@ -9020,7 +9020,7 @@ 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);

kernel/sched/rt.c

+6 −3
Original line number Diff line number Diff line
@@ -495,6 +495,9 @@ 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);
@@ -507,9 +510,9 @@ 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)

kernel/sched/sched.h

+7 −0
Original line number Diff line number Diff line
@@ -2165,6 +2165,13 @@ 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