[RFC PATCH v5 23/29] sched/rt: Hook HCBS migration functions

Yuri Andriaccio
2026-04-30T21:39:19Z

From: luca abeni <luca.abeni@santannapisa.it>

Hook rt-cgroup migration functions:

- balance_rt
- set_next_task_rt
- task_woken_rt
- switched_from_rt
- switched_to_rt
- prio_changed_rt
Follow the same patterns as for the standard FIFO/RR scheduling, but for
HCBS cgroups.

- put_prev_task_rt
If a server is throttled, put_prev_task_rt is invoked and a push is
necessary so that the task can keep running on another server if possible.

Update select_task_rq_rt to always return the cpu where the task is scheduled.

Update switched_to_rt to keep track of the deadline server that is assigned to
the task switching to FIFO/RR priority.

Co-developed-by: Alessio Balsini <a.balsini@sssup.it>
Signed-off-by: Alessio Balsini <a.balsini@sssup.it>
Co-developed-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Andrea Parri <parri.andrea@gmail.com>
Co-developed-by: Yuri Andriaccio <yurand2000@gmail.com>
Signed-off-by: Yuri Andriaccio <yurand2000@gmail.com>
Signed-off-by: luca abeni <luca.abeni@santannapisa.it>
---
kernel/sched/rt.c | 59 ++++++++++++++++++++++++++++++++++++-----------
1 file changed, 45 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index e1731e01757b..e6b3efa358d3 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1,4 +1,3 @@
-#pragma GCC diagnostic ignored "-Wunused-function"
// SPDX-License-Identifier: GPL-2.0
/*
* Real-Time Scheduling Class (mapped to the SCHED_FIFO and SCHED_RR
@@ -906,6 +905,11 @@ select_task_rq_rt(struct task_struct *p, int cpu, int flags)
struct rq *rq;
bool test;

+ /* Just return the task_cpu for processes inside task groups */
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) &&
+ is_dl_group(rt_rq_of_se(&p->rt)))
+ goto out;
+
/* For anything but wake ups, just return the task_cpu */
if (!(flags & (WF_TTWU | WF_FORK)))
goto out;
@@ -1005,7 +1009,10 @@ static int balance_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
* not yet started the picking loop.
*/
rq_unpin_lock(rq, rf);
- pull_rt_task(rq);
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq_of_se(&p->rt)))
+ group_pull_rt_task(rt_rq_of_se(&p->rt));
+ else
+ pull_rt_task(rq);
rq_repin_lock(rq, rf);
}

@@ -1120,7 +1127,9 @@ static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool f
if (rq->donor->sched_class != &rt_sched_class)
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);

- if (!IS_ENABLED(CONFIG_RT_GROUP_SCHED) || !is_dl_group(rt_rq))
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq))
+ rt_queue_push_from_group(rt_rq);
+ else
rt_queue_push_tasks(rt_rq);
}

@@ -1174,6 +1183,13 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p, struct task_s
*/
if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1)
enqueue_pushable_task(rt_rq, p);
+
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq)) {
+ struct sched_dl_entity *dl_se = dl_group_of(rt_rq);
+
+ if (dl_se->dl_throttled)
+ rt_queue_push_from_group(rt_rq);
+ }
}

/* Only try algorithms three times */
@@ -2214,6 +2230,7 @@ static void group_push_rt_tasks(struct rt_rq *rt_rq) { }
*/
static void task_woken_rt(struct rq *rq, struct task_struct *p)
{
+ struct rt_rq *rt_rq = rt_rq_of_se(&p->rt);
bool need_to_push = !task_on_cpu(rq, p) &&
!test_tsk_need_resched(rq->curr) &&
p->nr_cpus_allowed > 1 &&
@@ -2221,7 +2238,12 @@ static void task_woken_rt(struct rq *rq, struct task_struct *p)
(rq->curr->nr_cpus_allowed < 2 ||
rq->donor->prio <= p->prio);

- if (need_to_push)
+ if (!need_to_push)
+ return;
+
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq))
+ group_push_rt_tasks(rt_rq);
+ else
push_rt_tasks(rq);
}

@@ -2261,7 +2283,9 @@ static void switched_from_rt(struct rq *rq, struct task_struct *p)
if (!task_on_rq_queued(p) || rt_rq->rt_nr_running)
return;

- if (!IS_ENABLED(CONFIG_RT_GROUP_SCHED) || !is_dl_group(rt_rq))
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq))
+ rt_queue_pull_to_group(rt_rq);
+ else
rt_queue_pull_task(rt_rq);
}

@@ -2290,6 +2314,13 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
*/
if (task_current(rq, p)) {
update_rt_rq_load_avg(rq_clock_pelt(rq), rq, 0);
+
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq_of_se(&p->rt))) {
+ struct sched_dl_entity *dl_se = dl_group_of(rt_rq_of_se(&p->rt));
+
+ p->dl_server = dl_se;
+ }
+
return;
}

@@ -2299,13 +2330,10 @@ static void switched_to_rt(struct rq *rq, struct task_struct *p)
* then see if we can move to another run queue.
*/
if (task_on_rq_queued(p)) {
- if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq)) {
- if (p->prio < rq->donor->prio)
- resched_curr(rq);
- } else {
- if (p->nr_cpus_allowed > 1 && rq->rt.overloaded)
- rt_queue_push_tasks(rt_rq_of_se(&p->rt));
- }
+ if (!is_dl_group(rt_rq) && p->nr_cpus_allowed > 1 && rq->rt.overloaded)
+ rt_queue_push_tasks(rt_rq);
+ else if (is_dl_group(rt_rq) && rt_rq->overloaded)
+ rt_queue_push_from_group(rt_rq);

if (p->prio < rq->donor->prio && cpu_online(cpu_of(rq)))
resched_curr(rq);
@@ -2332,9 +2360,12 @@ prio_changed_rt(struct rq *rq, struct task_struct *p, u64 oldprio)
* If our priority decreases while running, we
* may need to pull tasks to this runqueue.
*/
- if (oldprio < p->prio)
- if (!IS_ENABLED(CONFIG_RT_GROUP_SCHED) || !is_dl_group(rt_rq))
+ if (oldprio < p->prio) {
+ if (IS_ENABLED(CONFIG_RT_GROUP_SCHED) && is_dl_group(rt_rq))
+ rt_queue_pull_to_group(rt_rq);
+ else
rt_queue_pull_task(rt_rq);
+ }

/*
* If there's a higher priority task waiting to run
--
2.53.0