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Message-ID: <176060721661.709179.13194764741989962419.tip-bot2@tip-bot2>
Date: Thu, 16 Oct 2025 09:33:36 -0000
From: "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Juri Lelli <juri.lelli@...hat.com>, Tejun Heo <tj@...nel.org>,
Vincent Guittot <vincent.guittot@...aro.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Fold sched_class::switch{ing,ed}_{to,from}()
into the change pattern
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 637b0682821b144d5993211cf0a768b322138a69
Gitweb: https://git.kernel.org/tip/637b0682821b144d5993211cf0a768b322138a69
Author: Peter Zijlstra <peterz@...radead.org>
AuthorDate: Wed, 30 Oct 2024 15:08:15 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Thu, 16 Oct 2025 11:13:51 +02:00
sched: Fold sched_class::switch{ing,ed}_{to,from}() into the change pattern
Add {DE,EN}QUEUE_CLASS and fold the sched_class::switch* methods into
the change pattern. This completes and makes the pattern more
symmetric.
This changes the order of callbacks slightly:
OLD NEW
|
| switching_from()
dequeue_task(); | dequeue_task()
put_prev_task(); | put_prev_task()
| switched_from()
|
... change task ... | ... change task ...
|
switching_to(); | switching_to()
enqueue_task(); | enqueue_task()
set_next_task(); | set_next_task()
prev_class->switched_from() |
switched_to() | switched_to()
|
Notably, it moves the switched_from() callback right after the
dequeue/put. Existing implementations don't appear to be affected by
this change in location -- specifically the task isn't enqueued on the
class in question in either location.
Make (CLASS)^(SAVE|MOVE), because there is nothing to save-restore
when changing scheduling classes.
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Juri Lelli <juri.lelli@...hat.com>
Acked-by: Tejun Heo <tj@...nel.org>
Acked-by: Vincent Guittot <vincent.guittot@...aro.org>
---
kernel/sched/core.c | 51 ++++++++++++++++-----------------------
kernel/sched/ext.c | 22 ++++++++++++-----
kernel/sched/idle.c | 4 +--
kernel/sched/rt.c | 2 +-
kernel/sched/sched.h | 22 ++++++-----------
kernel/sched/stop_task.c | 4 +--
kernel/sched/syscalls.c | 7 +++--
7 files changed, 55 insertions(+), 57 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index eca40df..4dbd206 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2169,34 +2169,9 @@ inline int task_curr(const struct task_struct *p)
return cpu_curr(task_cpu(p)) == p;
}
-/*
- * ->switching_to() is called with the pi_lock and rq_lock held and must not
- * mess with locking.
- */
-void check_class_changing(struct rq *rq, struct task_struct *p,
- const struct sched_class *prev_class)
-{
- if (prev_class != p->sched_class && p->sched_class->switching_to)
- p->sched_class->switching_to(rq, p);
-}
-
-/*
- * switched_from, switched_to and prio_changed must _NOT_ drop rq->lock,
- * use the balance_callback list if you want balancing.
- *
- * this means any call to check_class_changed() must be followed by a call to
- * balance_callback().
- */
-void check_class_changed(struct rq *rq, struct task_struct *p,
- const struct sched_class *prev_class,
- int oldprio)
+void check_prio_changed(struct rq *rq, struct task_struct *p, int oldprio)
{
- if (prev_class != p->sched_class) {
- if (prev_class->switched_from)
- prev_class->switched_from(rq, p);
-
- p->sched_class->switched_to(rq, p);
- } else if (oldprio != p->prio || dl_task(p))
+ if (oldprio != p->prio || dl_task(p))
p->sched_class->prio_changed(rq, p, oldprio);
}
@@ -7388,6 +7363,9 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
prev_class = p->sched_class;
next_class = __setscheduler_class(p->policy, prio);
+ if (prev_class != next_class)
+ queue_flag |= DEQUEUE_CLASS;
+
if (prev_class != next_class && p->se.sched_delayed)
dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
@@ -7424,11 +7402,10 @@ void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task)
p->sched_class = next_class;
p->prio = prio;
-
- check_class_changing(rq, p, prev_class);
}
- check_class_changed(rq, p, prev_class, oldprio);
+ if (!(queue_flag & DEQUEUE_CLASS))
+ check_prio_changed(rq, p, oldprio);
out_unlock:
/* Avoid rq from going away on us: */
preempt_disable();
@@ -10862,6 +10839,11 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int
lockdep_assert_rq_held(rq);
+ if (flags & DEQUEUE_CLASS) {
+ if (p->sched_class->switching_from)
+ p->sched_class->switching_from(rq, p);
+ }
+
*ctx = (struct sched_change_ctx){
.p = p,
.flags = flags,
@@ -10874,6 +10856,9 @@ struct sched_change_ctx *sched_change_begin(struct task_struct *p, unsigned int
if (ctx->running)
put_prev_task(rq, p);
+ if ((flags & DEQUEUE_CLASS) && p->sched_class->switched_from)
+ p->sched_class->switched_from(rq, p);
+
return ctx;
}
@@ -10884,8 +10869,14 @@ void sched_change_end(struct sched_change_ctx *ctx)
lockdep_assert_rq_held(rq);
+ if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switching_to)
+ p->sched_class->switching_to(rq, p);
+
if (ctx->queued)
enqueue_task(rq, p, ctx->flags | ENQUEUE_NOCLOCK);
if (ctx->running)
set_next_task(rq, p);
+
+ if ((ctx->flags & ENQUEUE_CLASS) && p->sched_class->switched_to)
+ p->sched_class->switched_to(rq, p);
}
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 4566a7c..a408c39 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3912,21 +3912,26 @@ static void scx_disable_workfn(struct kthread_work *work)
scx_task_iter_start(&sti);
while ((p = scx_task_iter_next_locked(&sti))) {
+ unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
const struct sched_class *old_class = p->sched_class;
const struct sched_class *new_class =
__setscheduler_class(p->policy, p->prio);
update_rq_clock(task_rq(p));
+ if (old_class != new_class)
+ queue_flags |= DEQUEUE_CLASS;
+
if (old_class != new_class && p->se.sched_delayed)
dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK) {
+ scoped_guard (sched_change, p, queue_flags) {
p->sched_class = new_class;
- check_class_changing(task_rq(p), p, old_class);
}
- check_class_changed(task_rq(p), p, old_class, p->prio);
+ if (!(queue_flags & DEQUEUE_CLASS))
+ check_prio_changed(task_rq(p), p, p->prio);
+
scx_exit_task(p);
}
scx_task_iter_stop(&sti);
@@ -4655,6 +4660,7 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
percpu_down_write(&scx_fork_rwsem);
scx_task_iter_start(&sti);
while ((p = scx_task_iter_next_locked(&sti))) {
+ unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
const struct sched_class *old_class = p->sched_class;
const struct sched_class *new_class =
__setscheduler_class(p->policy, p->prio);
@@ -4664,16 +4670,20 @@ static int scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
update_rq_clock(task_rq(p));
+ if (old_class != new_class)
+ queue_flags |= DEQUEUE_CLASS;
+
if (old_class != new_class && p->se.sched_delayed)
dequeue_task(task_rq(p), p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK) {
+ scoped_guard (sched_change, p, queue_flags) {
p->scx.slice = SCX_SLICE_DFL;
p->sched_class = new_class;
- check_class_changing(task_rq(p), p, old_class);
}
- check_class_changed(task_rq(p), p, old_class, p->prio);
+ if (!(queue_flags & DEQUEUE_CLASS))
+ check_prio_changed(task_rq(p), p, p->prio);
+
put_task_struct(p);
}
scx_task_iter_stop(&sti);
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index c39b089..f02dced 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -498,7 +498,7 @@ static void task_tick_idle(struct rq *rq, struct task_struct *curr, int queued)
{
}
-static void switched_to_idle(struct rq *rq, struct task_struct *p)
+static void switching_to_idle(struct rq *rq, struct task_struct *p)
{
BUG();
}
@@ -536,6 +536,6 @@ DEFINE_SCHED_CLASS(idle) = {
.task_tick = task_tick_idle,
.prio_changed = prio_changed_idle,
- .switched_to = switched_to_idle,
+ .switching_to = switching_to_idle,
.update_curr = update_curr_idle,
};
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 7936d43..6b2e811 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2589,8 +2589,8 @@ DEFINE_SCHED_CLASS(rt) = {
.get_rr_interval = get_rr_interval_rt,
- .prio_changed = prio_changed_rt,
.switched_to = switched_to_rt,
+ .prio_changed = prio_changed_rt,
.update_curr = update_curr_rt,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 24b3c6c..e3f4215 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -20,7 +20,6 @@
#include <linux/sched/task_flags.h>
#include <linux/sched/task.h>
#include <linux/sched/topology.h>
-
#include <linux/atomic.h>
#include <linux/bitmap.h>
#include <linux/bug.h>
@@ -2369,6 +2368,7 @@ extern const u32 sched_prio_to_wmult[40];
#define DEQUEUE_MIGRATING 0x0010 /* Matches ENQUEUE_MIGRATING */
#define DEQUEUE_DELAYED 0x0020 /* Matches ENQUEUE_DELAYED */
+#define DEQUEUE_CLASS 0x0040 /* Matches ENQUEUE_CLASS */
#define DEQUEUE_SPECIAL 0x00010000
#define DEQUEUE_THROTTLE 0x00020000
@@ -2380,6 +2380,7 @@ extern const u32 sched_prio_to_wmult[40];
#define ENQUEUE_MIGRATING 0x0010
#define ENQUEUE_DELAYED 0x0020
+#define ENQUEUE_CLASS 0x0040
#define ENQUEUE_HEAD 0x00010000
#define ENQUEUE_REPLENISH 0x00020000
@@ -2443,14 +2444,11 @@ struct sched_class {
void (*task_fork)(struct task_struct *p);
void (*task_dead)(struct task_struct *p);
- /*
- * The switched_from() call is allowed to drop rq->lock, therefore we
- * cannot assume the switched_from/switched_to pair is serialized by
- * rq->lock. They are however serialized by p->pi_lock.
- */
- void (*switching_to) (struct rq *this_rq, struct task_struct *task);
- void (*switched_from)(struct rq *this_rq, struct task_struct *task);
- void (*switched_to) (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);
+ void (*switched_to) (struct rq *this_rq, struct task_struct *task);
+
void (*reweight_task)(struct rq *this_rq, struct task_struct *task,
const struct load_weight *lw);
void (*prio_changed) (struct rq *this_rq, struct task_struct *task,
@@ -3879,11 +3877,7 @@ extern void set_load_weight(struct task_struct *p, bool update_load);
extern void enqueue_task(struct rq *rq, struct task_struct *p, int flags);
extern bool dequeue_task(struct rq *rq, struct task_struct *p, int flags);
-extern void check_class_changing(struct rq *rq, struct task_struct *p,
- const struct sched_class *prev_class);
-extern void check_class_changed(struct rq *rq, struct task_struct *p,
- const struct sched_class *prev_class,
- int oldprio);
+extern void check_prio_changed(struct rq *rq, struct task_struct *p, int oldprio);
extern struct balance_callback *splice_balance_callbacks(struct rq *rq);
extern void balance_callbacks(struct rq *rq, struct balance_callback *head);
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 2d4e279..fcc4c54 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -75,7 +75,7 @@ static void task_tick_stop(struct rq *rq, struct task_struct *curr, int queued)
{
}
-static void switched_to_stop(struct rq *rq, struct task_struct *p)
+static void switching_to_stop(struct rq *rq, struct task_struct *p)
{
BUG(); /* its impossible to change to this class */
}
@@ -112,6 +112,6 @@ DEFINE_SCHED_CLASS(stop) = {
.task_tick = task_tick_stop,
.prio_changed = prio_changed_stop,
- .switched_to = switched_to_stop,
+ .switching_to = switching_to_stop,
.update_curr = update_curr_stop,
};
diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index 09ffe91..bcef5c7 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -684,6 +684,9 @@ change:
prev_class = p->sched_class;
next_class = __setscheduler_class(policy, newprio);
+ if (prev_class != next_class)
+ queue_flags |= DEQUEUE_CLASS;
+
if (prev_class != next_class && p->se.sched_delayed)
dequeue_task(rq, p, DEQUEUE_SLEEP | DEQUEUE_DELAYED | DEQUEUE_NOCLOCK);
@@ -695,7 +698,6 @@ change:
p->prio = newprio;
}
__setscheduler_uclamp(p, attr);
- check_class_changing(rq, p, prev_class);
if (scope->queued) {
/*
@@ -707,7 +709,8 @@ change:
}
}
- check_class_changed(rq, p, prev_class, oldprio);
+ if (!(queue_flags & DEQUEUE_CLASS))
+ check_prio_changed(rq, p, oldprio);
/* Avoid rq from going away on us: */
preempt_disable();
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