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Message-ID: <20251006104527.928947651@infradead.org>
Date: Mon, 06 Oct 2025 12:44:14 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: tj@...nel.org
Cc: linux-kernel@...r.kernel.org,
peterz@...radead.org,
mingo@...nel.org,
juri.lelli@...hat.com,
vincent.guittot@...aro.org,
dietmar.eggemann@....com,
rostedt@...dmis.org,
bsegall@...gle.com,
mgorman@...e.de,
vschneid@...hat.com,
longman@...hat.com,
hannes@...xchg.org,
mkoutny@...e.com,
void@...ifault.com,
arighi@...dia.com,
changwoo@...lia.com,
cgroups@...r.kernel.org,
sched-ext@...ts.linux.dev,
liuwenfang@...or.com,
tglx@...utronix.de,
K Prateek Nayak <kprateek.nayak@....com>
Subject: [PATCH 12/12] sched: Cleanup the sched_change NOCLOCK usage
Teach the sched_change pattern how to do update_rq_clock(); this
allows for some simplifications / cleanups.
Suggested-by: K Prateek Nayak <kprateek.nayak@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
kernel/sched/core.c | 33 +++++++++++----------------------
kernel/sched/ext.c | 8 ++------
kernel/sched/syscalls.c | 8 ++------
3 files changed, 15 insertions(+), 34 deletions(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2346,10 +2346,8 @@ static void migrate_disable_switch(struc
if (p->cpus_ptr != &p->cpus_mask)
return;
- scoped_guard (task_rq_lock, p) {
- update_rq_clock(scope.rq);
+ scoped_guard (task_rq_lock, p)
do_set_cpus_allowed(p, &ac);
- }
}
void ___migrate_enable(void)
@@ -2666,9 +2664,7 @@ void set_cpus_allowed_common(struct task
static void
do_set_cpus_allowed(struct task_struct *p, struct affinity_context *ctx)
{
- u32 flags = DEQUEUE_SAVE | DEQUEUE_NOCLOCK;
-
- scoped_guard (sched_change, p, flags) {
+ scoped_guard (sched_change, p, DEQUEUE_SAVE) {
p->sched_class->set_cpus_allowed(p, ctx);
mm_set_cpus_allowed(p->mm, ctx->new_mask);
}
@@ -2690,10 +2686,8 @@ void set_cpus_allowed_force(struct task_
struct rcu_head rcu;
};
- scoped_guard (__task_rq_lock, p) {
- update_rq_clock(scope.rq);
+ scoped_guard (__task_rq_lock, p)
do_set_cpus_allowed(p, &ac);
- }
/*
* Because this is called with p->pi_lock held, it is not possible
@@ -9110,16 +9104,13 @@ static void sched_change_group(struct ta
*/
void sched_move_task(struct task_struct *tsk, bool for_autogroup)
{
- unsigned int queue_flags =
- DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
+ unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
bool resched = false;
struct rq *rq;
CLASS(task_rq_lock, rq_guard)(tsk);
rq = rq_guard.rq;
- update_rq_clock(rq);
-
scoped_guard (sched_change, tsk, queue_flags) {
sched_change_group(tsk);
if (!for_autogroup)
@@ -10794,19 +10785,17 @@ struct sched_change_ctx *sched_change_be
lockdep_assert_rq_held(rq);
+ if (!(flags & DEQUEUE_NOCLOCK)) {
+ update_rq_clock(rq);
+ flags |= DEQUEUE_NOCLOCK;
+ }
+
if (flags & DEQUEUE_CLASS) {
if (WARN_ON_ONCE(flags & (DEQUEUE_SAVE | DEQUEUE_MOVE)))
flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE);
- if (p->sched_class->switching_from) {
- /*
- * switching_from_fair() assumes CLASS implies NOCLOCK;
- * fixing this assumption would mean switching_from()
- * would need to be able to change flags.
- */
- WARN_ON(!(flags & DEQUEUE_NOCLOCK));
+ if (p->sched_class->switching_from)
p->sched_class->switching_from(rq, p);
- }
}
*ctx = (struct sched_change_ctx){
@@ -10845,7 +10834,7 @@ void sched_change_end(struct sched_chang
p->sched_class->switching_to(rq, p);
if (ctx->queued)
- enqueue_task(rq, p, ctx->flags | ENQUEUE_NOCLOCK);
+ enqueue_task(rq, p, ctx->flags);
if (ctx->running)
set_next_task(rq, p);
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -3912,13 +3912,11 @@ static void scx_disable_workfn(struct kt
scx_task_iter_start(&sti);
while ((p = scx_task_iter_next_locked(&sti))) {
- unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
+ unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
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;
queue_flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE);
@@ -4656,7 +4654,7 @@ static int scx_enable(struct sched_ext_o
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;
+ unsigned int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE;
const struct sched_class *old_class = p->sched_class;
const struct sched_class *new_class =
__setscheduler_class(p->policy, p->prio);
@@ -4664,8 +4662,6 @@ static int scx_enable(struct sched_ext_o
if (!tryget_task_struct(p))
continue;
- update_rq_clock(task_rq(p));
-
if (old_class != new_class) {
queue_flags |= DEQUEUE_CLASS;
queue_flags &= ~(DEQUEUE_SAVE | DEQUEUE_MOVE);
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -64,7 +64,6 @@ static int effective_prio(struct task_st
void set_user_nice(struct task_struct *p, long nice)
{
- struct rq *rq;
int old_prio;
if (task_nice(p) == nice || nice < MIN_NICE || nice > MAX_NICE)
@@ -73,10 +72,7 @@ void set_user_nice(struct task_struct *p
* We have to be careful, if called from sys_setpriority(),
* the task might be in the middle of scheduling on another CPU.
*/
- CLASS(task_rq_lock, rq_guard)(p);
- rq = rq_guard.rq;
-
- update_rq_clock(rq);
+ guard(task_rq_lock)(p);
/*
* The RT priorities are set via sched_setscheduler(), but we still
@@ -89,7 +85,7 @@ void set_user_nice(struct task_struct *p
return;
}
- scoped_guard (sched_change, p, DEQUEUE_SAVE | DEQUEUE_NOCLOCK) {
+ scoped_guard (sched_change, p, DEQUEUE_SAVE) {
p->static_prio = NICE_TO_PRIO(nice);
set_load_weight(p, true);
old_prio = p->prio;
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