[PATCH 04/14] sched: Add prepare_switch() class callback
From: Andrea Righi
Date: Sat Jul 25 2026 - 12:07:35 EST
sched_change_begin() only invokes callbacks on the outgoing class before
recording the task queueing state. An incoming class may need to prepare
a task while that state is still live, before the normal dequeue and
class transition take place.
Pass the incoming class to sched_change_begin() and invoke its optional
prepare_switch() callback before recording the queued and running state.
This is a preparatory change to support proxy execution with sched_ext.
Suggested-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Andrea Righi <arighi@xxxxxxxxxx>
---
kernel/sched/core.c | 16 +++++++++++-----
kernel/sched/ext/ext.c | 7 ++++---
kernel/sched/ext/sub.c | 9 ++++++---
kernel/sched/sched.h | 10 +++++++---
kernel/sched/syscalls.c | 4 ++--
5 files changed, 30 insertions(+), 16 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9a9d4b5040089..474628f520a29 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2792,7 +2792,7 @@ void set_cpus_allowed_common(struct task_struct *p, struct affinity_context *ctx
static void
do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
{
- scoped_guard (sched_change, p, DEQUEUE_SAVE)
+ scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE)
p->sched_class->set_cpus_allowed(p, ctx);
}
@@ -7722,7 +7722,7 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
if (prev_class != next_class)
queue_flag |= DEQUEUE_CLASS;
- scoped_guard (sched_change, p, queue_flag) {
+ scoped_guard (sched_change, p, next_class, queue_flag) {
/*
* Boosting condition are:
* 1. -rt task is running and holds mutex A
@@ -8399,7 +8399,7 @@ int migrate_task_to(struct task_struct *p, int target_cpu)
void sched_setnuma(struct task_struct *p, int nid)
{
guard(task_rq_lock)(p);
- scoped_guard (sched_change, p, DEQUEUE_SAVE)
+ scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE)
p->numa_preferred_nid = nid;
}
#endif /* CONFIG_NUMA_BALANCING */
@@ -9516,7 +9516,7 @@ void sched_move_task(struct task_struct *tsk, bool for_autogroup)
CLASS(task_rq_lock, rq_guard)(tsk);
rq = rq_guard.rq;
- scoped_guard (sched_change, tsk, queue_flags) {
+ scoped_guard (sched_change, tsk, tsk->sched_class, queue_flags) {
sched_change_group(tsk);
if (!for_autogroup)
scx_cgroup_move_task(tsk);
@@ -11220,7 +11220,9 @@ static inline void sched_mm_cid_fork(struct task_struct *t) { }
static DEFINE_PER_CPU(struct sched_change_ctx, sched_change_ctx);
-struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags)
+struct sched_change_ctx *
+sched_change_begin(struct task_struct *p, const struct sched_class *next_class,
+ unsigned int flags)
{
struct sched_change_ctx *ctx = this_cpu_ptr(&sched_change_ctx);
struct rq *rq = task_rq(p);
@@ -11238,6 +11240,10 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int
flags |= DEQUEUE_NOCLOCK;
}
+ if ((flags & DEQUEUE_CLASS) && next_class != p->sched_class &&
+ next_class->prepare_switch)
+ next_class->prepare_switch(rq, p);
+
if ((flags & DEQUEUE_CLASS) && p->sched_class->switching_from)
p->sched_class->switching_from(rq, p);
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 81c2d8eeae410..285bd8422193d 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -5859,7 +5859,8 @@ void scx_bypass(struct scx_sched *sch, bool bypass)
continue;
/* cycling deq/enq is enough, see the function comment */
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+ scoped_guard (sched_change, p, p->sched_class,
+ DEQUEUE_SAVE | DEQUEUE_MOVE) {
/* nothing */ ;
}
}
@@ -6141,7 +6142,7 @@ static void scx_root_disable(struct scx_sched *sch)
if (old_class != new_class)
queue_flags |= DEQUEUE_CLASS;
- scoped_guard (sched_change, p, queue_flags) {
+ scoped_guard (sched_change, p, new_class, queue_flags) {
p->sched_class = new_class;
}
@@ -7477,7 +7478,7 @@ static void scx_root_enable_workfn(struct kthread_work *work)
if (old_class != new_class)
queue_flags |= DEQUEUE_CLASS;
- scoped_guard (sched_change, p, queue_flags) {
+ scoped_guard (sched_change, p, new_class, queue_flags) {
set_task_slice(p, READ_ONCE(sch->slice_dfl));
p->sched_class = new_class;
}
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index 6da6c91e42870..765b516e06c95 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -791,7 +791,8 @@ static void scx_rehome_task(struct scx_sched *to, struct task_struct *p)
lockdep_assert_held(&p->pi_lock);
lockdep_assert_rq_held(task_rq(p));
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+ scoped_guard (sched_change, p, p->sched_class,
+ DEQUEUE_SAVE | DEQUEUE_MOVE) {
scx_disable_and_exit_task(scx_task_sched(p), p);
scx_set_task_state(p, SCX_TASK_INIT_BEGIN);
scx_set_task_state(p, SCX_TASK_INIT);
@@ -821,7 +822,8 @@ static void scx_punt_task(struct scx_sched *to, struct task_struct *p)
lockdep_assert_rq_held(task_rq(p));
WARN_ON_ONCE(!READ_ONCE(to->bypass_depth));
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+ scoped_guard (sched_change, p, p->sched_class,
+ DEQUEUE_SAVE | DEQUEUE_MOVE) {
scx_disable_and_exit_task(scx_task_sched(p), p);
scx_set_task_sched(p, to);
}
@@ -1471,7 +1473,8 @@ void scx_sub_enable_workfn(struct kthread_work *work)
if (!(p->scx.flags & SCX_TASK_SUB_INIT))
continue;
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE) {
+ scoped_guard (sched_change, p, p->sched_class,
+ DEQUEUE_SAVE | DEQUEUE_MOVE) {
/*
* $p must be either READY or ENABLED. If ENABLED,
* __scx_disabled_and_exit_task() first disables and
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 437c4f68c9e53..ca436a8174d30 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2705,6 +2705,7 @@ struct sched_class {
/*
* sched_change
*/
+ void (*prepare_switch)(struct rq *this_rq, struct task_struct *task);
void (*switching_from)(struct rq *this_rq, struct task_struct *task);
void (*switched_from) (struct rq *this_rq, struct task_struct *task);
void (*switching_to) (struct rq *this_rq, struct task_struct *task);
@@ -4214,13 +4215,16 @@ struct sched_change_ctx {
bool running;
};
-struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int flags);
+struct sched_change_ctx *
+sched_change_begin(struct task_struct *p, const struct sched_class *next_class,
+ unsigned int flags);
void sched_change_end(struct sched_change_ctx *ctx);
DEFINE_CLASS(sched_change, struct sched_change_ctx *,
sched_change_end(_T),
- sched_change_begin(p, flags),
- struct task_struct *p, unsigned int flags)
+ sched_change_begin(p, next_class, flags),
+ struct task_struct *p, const struct sched_class *next_class,
+ unsigned int flags)
DEFINE_CLASS_IS_UNCONDITIONAL(sched_change)
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index b215b0ead9a60..bc32ce76ff4fe 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -85,7 +85,7 @@ void set_user_nice(struct task_struct *p, long nice)
return;
}
- scoped_guard (sched_change, p, DEQUEUE_SAVE) {
+ scoped_guard (sched_change, p, p->sched_class, DEQUEUE_SAVE) {
p->static_prio = NICE_TO_PRIO(nice);
set_load_weight(p, true);
old_prio = p->prio;
@@ -678,7 +678,7 @@ int __sched_setscheduler(struct task_struct *p,
if (prev_class != next_class)
queue_flags |= DEQUEUE_CLASS;
- scoped_guard (sched_change, p, queue_flags) {
+ scoped_guard (sched_change, p, next_class, queue_flags) {
if (!(attr->sched_flags & SCHED_FLAG_KEEP_PARAMS)) {
__setscheduler_params(p, attr);
--
2.55.0