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sched: Skip non-root task_groups with disabled RT_GROUP_SCHED

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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@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250310170442.504716-6-mkoutny@suse.com
This commit is contained in:
Michal Koutný 2025-03-10 18:04:37 +01:00 committed by Peter Zijlstra
parent e34e0131fe
commit 61d3164fec
3 changed files with 14 additions and 4 deletions
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2
kernel/sched/core.c
View File

@ -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);

9
kernel/sched/rt.c
View File

@ -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)

7
kernel/sched/sched.h
View File

@ -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