[PATCH 0/4] sched_ext: Standardize preprocessor comment markers

[PATCH 0/4] sched_ext: Standardize preprocessor comment markers

[Cheng-Yang Chou]

This series standardizes `#if/#else/#endif` comment markers in the
`sched/ext*.{c,h}` files for consistency and readability.

It follows the direction of Ingo Molnar's recent cleanup
("[PATCH 00/43] sched: Use the SMP scheduler on UP too"), which reduced
`CONFIG_SMP` complexity and removed many `#ifdef` blocks across the scheduler.

No functional change.

Thanks.

-chengyang

---
Cheng-Yang Chou (4):
  sched_ext: Clean up and standardize #if/#else/#endif markers in
    sched/ext.c
  sched_ext: Clean up and standardize #if/#else/#endif markers in
    sched/ext.h
  sched_ext: Clean up and standardize #if/#else/#endif markers in
    sched/ext_idle.c
  sched_ext: Clean up and standardize #if/#else/#endif markers in
    sched/ext_idle.h

 kernel/sched/ext.c      | 26 +-------------------------
 kernel/sched/ext.h      |  2 +-
 kernel/sched/ext_idle.c | 25 +------------------------
 kernel/sched/ext_idle.h | 10 ----------
 4 files changed, 3 insertions(+), 60 deletions(-)

-- 
2.43.0

[PATCH 1/4] sched_ext: Clean up and standardize #if/#else/#endif markers in sched/ext.c

[Cheng-Yang Chou]

Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 kernel/sched/ext.c | 26 +-------------------------
 1 file changed, 1 insertion(+), 25 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 2c41c78be61e..55702b7a72e2 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1792,12 +1792,10 @@ static void run_deferred(struct rq *rq)
 	process_ddsp_deferred_locals(rq);
 }
 
-#ifdef CONFIG_SMP
 static void deferred_bal_cb_workfn(struct rq *rq)
 {
 	run_deferred(rq);
 }
-#endif
 
 static void deferred_irq_workfn(struct irq_work *irq_work)
 {
@@ -1820,7 +1818,6 @@ static void schedule_deferred(struct rq *rq)
 {
 	lockdep_assert_rq_held(rq);
 
-#ifdef CONFIG_SMP
 	/*
 	 * If in the middle of waking up a task, task_woken_scx() will be called
 	 * afterwards which will then run the deferred actions, no need to
@@ -1838,7 +1835,7 @@ static void schedule_deferred(struct rq *rq)
 				       deferred_bal_cb_workfn);
 		return;
 	}
-#endif
+
 	/*
 	 * No scheduler hooks available. Queue an irq work. They are executed on
 	 * IRQ re-enable which may take a bit longer than the scheduler hooks.
@@ -2542,7 +2539,6 @@ static void move_local_task_to_local_dsq(struct task_struct *p, u64 enq_flags,
 	p->scx.dsq = dst_dsq;
 }
 
-#ifdef CONFIG_SMP
 /**
  * move_remote_task_to_local_dsq - Move a task from a foreign rq to a local DSQ
  * @p: task to move
@@ -2709,11 +2705,6 @@ static bool consume_remote_task(struct rq *this_rq, struct task_struct *p,
 		return false;
 	}
 }
-#else	/* CONFIG_SMP */
-static inline void move_remote_task_to_local_dsq(struct task_struct *p, u64 enq_flags, struct rq *src_rq, struct rq *dst_rq) { WARN_ON_ONCE(1); }
-static inline bool task_can_run_on_remote_rq(struct scx_sched *sch, struct task_struct *p, struct rq *rq, bool enforce) { return false; }
-static inline bool consume_remote_task(struct rq *this_rq, struct task_struct *p, struct scx_dispatch_q *dsq, struct rq *task_rq) { return false; }
-#endif	/* CONFIG_SMP */
 
 /**
  * move_task_between_dsqs() - Move a task from one DSQ to another
@@ -2886,9 +2877,7 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 {
 	struct rq *src_rq = task_rq(p);
 	struct rq *dst_rq = container_of(dst_dsq, struct rq, scx.local_dsq);
-#ifdef CONFIG_SMP
 	struct rq *locked_rq = rq;
-#endif
 
 	/*
 	 * We're synchronized against dequeue through DISPATCHING. As @p can't
@@ -2902,7 +2891,6 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 		return;
 	}
 
-#ifdef CONFIG_SMP
 	if (src_rq != dst_rq &&
 	    unlikely(!task_can_run_on_remote_rq(sch, p, dst_rq, true))) {
 		dispatch_enqueue(sch, find_global_dsq(p), p,
@@ -2962,9 +2950,6 @@ static void dispatch_to_local_dsq(struct scx_sched *sch, struct rq *rq,
 		raw_spin_rq_unlock(locked_rq);
 		raw_spin_rq_lock(rq);
 	}
-#else	/* CONFIG_SMP */
-	BUG();	/* control can not reach here on UP */
-#endif	/* CONFIG_SMP */
 }
 
 /**
@@ -3288,10 +3273,8 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first)
 static enum scx_cpu_preempt_reason
 preempt_reason_from_class(const struct sched_class *class)
 {
-#ifdef CONFIG_SMP
 	if (class == &stop_sched_class)
 		return SCX_CPU_PREEMPT_STOP;
-#endif
 	if (class == &dl_sched_class)
 		return SCX_CPU_PREEMPT_DL;
 	if (class == &rt_sched_class)
@@ -3304,14 +3287,12 @@ static void switch_class(struct rq *rq, struct task_struct *next)
 	struct scx_sched *sch = scx_root;
 	const struct sched_class *next_class = next->sched_class;
 
-#ifdef CONFIG_SMP
 	/*
 	 * Pairs with the smp_load_acquire() issued by a CPU in
 	 * kick_cpus_irq_workfn() who is waiting for this CPU to perform a
 	 * resched.
 	 */
 	smp_store_release(&rq->scx.pnt_seq, rq->scx.pnt_seq + 1);
-#endif
 	if (!(sch->ops.flags & SCX_OPS_HAS_CPU_PREEMPT))
 		return;
 
@@ -3508,8 +3489,6 @@ bool scx_prio_less(const struct task_struct *a, const struct task_struct *b,
 }
 #endif	/* CONFIG_SCHED_CORE */
 
-#ifdef CONFIG_SMP
-
 static int select_task_rq_scx(struct task_struct *p, int prev_cpu, int wake_flags)
 {
 	struct scx_sched *sch = scx_root;
@@ -3639,7 +3618,6 @@ static void rq_offline_scx(struct rq *rq)
 	rq->scx.flags &= ~SCX_RQ_ONLINE;
 }
 
-#endif	/* CONFIG_SMP */
 
 static bool check_rq_for_timeouts(struct rq *rq)
 {
@@ -4299,14 +4277,12 @@ DEFINE_SCHED_CLASS(ext) = {
 	.put_prev_task		= put_prev_task_scx,
 	.set_next_task		= set_next_task_scx,
 
-#ifdef CONFIG_SMP
 	.select_task_rq		= select_task_rq_scx,
 	.task_woken		= task_woken_scx,
 	.set_cpus_allowed	= set_cpus_allowed_scx,
 
 	.rq_online		= rq_online_scx,
 	.rq_offline		= rq_offline_scx,
-#endif
 
 	.task_tick		= task_tick_scx,
 
-- 
2.43.0

[PATCH 2/4] sched_ext: Clean up and standardize #if/#else/#endif markers in sched/ext.h

[Cheng-Yang Chou]

Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 kernel/sched/ext.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/ext.h b/kernel/sched/ext.h
index 6e5072f57771..d2f8cefae68c 100644
--- a/kernel/sched/ext.h
+++ b/kernel/sched/ext.h
@@ -65,7 +65,7 @@ static inline void init_sched_ext_class(void) {}
 
 #endif	/* CONFIG_SCHED_CLASS_EXT */
 
-#if defined(CONFIG_SCHED_CLASS_EXT) && defined(CONFIG_SMP)
+#if defined(CONFIG_SCHED_CLASS_EXT)
 void __scx_update_idle(struct rq *rq, bool idle, bool do_notify);
 
 static inline void scx_update_idle(struct rq *rq, bool idle, bool do_notify)
-- 
2.43.0

[PATCH 3/4] sched_ext: Clean up and standardize #if/#else/#endif markers in sched/ext_idle.c

[Cheng-Yang Chou]

Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 kernel/sched/ext_idle.c | 25 +------------------------
 1 file changed, 1 insertion(+), 24 deletions(-)

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 6d29d3cbc670..6d01cfe10875 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -17,7 +17,6 @@ static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
 /* Enable/disable per-node idle cpumasks */
 static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node);
 
-#ifdef CONFIG_SMP
 /* Enable/disable LLC aware optimizations */
 static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_llc);
 
@@ -794,7 +793,6 @@ static void reset_idle_masks(struct sched_ext_ops *ops)
 		cpumask_and(idle_cpumask(node)->smt, cpu_online_mask, node_mask);
 	}
 }
-#endif	/* CONFIG_SMP */
 
 void scx_idle_enable(struct sched_ext_ops *ops)
 {
@@ -808,9 +806,7 @@ void scx_idle_enable(struct sched_ext_ops *ops)
 	else
 		static_branch_disable_cpuslocked(&scx_builtin_idle_per_node);
 
-#ifdef CONFIG_SMP
 	reset_idle_masks(ops);
-#endif
 }
 
 void scx_idle_disable(void)
@@ -896,7 +892,6 @@ s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 	if (!rq)
 		lockdep_assert_held(&p->pi_lock);
 
-#ifdef CONFIG_SMP
 	/*
 	 * This may also be called from ops.enqueue(), so we need to handle
 	 * per-CPU tasks as well. For these tasks, we can skip all idle CPU
@@ -913,9 +908,7 @@ s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 		cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags,
 					 allowed ?: p->cpus_ptr, flags);
 	}
-#else
-	cpu = -EBUSY;
-#endif
+
 	if (scx_kf_allowed_if_unlocked())
 		task_rq_unlock(rq, p, &rf);
 
@@ -1010,11 +1003,7 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
 	if (node < 0)
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	return idle_cpumask(node)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1034,11 +1023,7 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
 	if (!check_builtin_idle_enabled())
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	return idle_cpumask(NUMA_NO_NODE)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1057,14 +1042,10 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
 	if (node < 0)
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	if (sched_smt_active())
 		return idle_cpumask(node)->smt;
 	else
 		return idle_cpumask(node)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1085,14 +1066,10 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask(void)
 	if (!check_builtin_idle_enabled())
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	if (sched_smt_active())
 		return idle_cpumask(NUMA_NO_NODE)->smt;
 	else
 		return idle_cpumask(NUMA_NO_NODE)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
-- 
2.43.0

[PATCH 4/4] sched_ext: Clean up and standardize #if/#else/#endif markers in sched/ext_idle.h

[Cheng-Yang Chou]

Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 kernel/sched/ext_idle.h | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/kernel/sched/ext_idle.h b/kernel/sched/ext_idle.h
index 37be78a7502b..906f1672c1d7 100644
--- a/kernel/sched/ext_idle.h
+++ b/kernel/sched/ext_idle.h
@@ -12,20 +12,10 @@
 
 struct sched_ext_ops;
 
-#ifdef CONFIG_SMP
 void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops);
 void scx_idle_init_masks(void);
 bool scx_idle_test_and_clear_cpu(int cpu);
 s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node, u64 flags);
-#else /* !CONFIG_SMP */
-static inline void scx_idle_update_selcpu_topology(struct sched_ext_ops *ops) {}
-static inline void scx_idle_init_masks(void) {}
-static inline bool scx_idle_test_and_clear_cpu(int cpu) { return false; }
-static inline s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node, u64 flags)
-{
-	return -EBUSY;
-}
-#endif /* CONFIG_SMP */
 
 s32 scx_select_cpu_dfl(struct task_struct *p, s32 prev_cpu, u64 wake_flags,
 		       const struct cpumask *cpus_allowed, u64 flags);
-- 
2.43.0

Re: [PATCH 0/4] sched_ext: Standardize preprocessor comment markers

[Tejun Heo]

On Wed, Jun 11, 2025 at 09:54:00PM +0800, Cheng-Yang Chou wrote:
> Cheng-Yang Chou (4):
>   sched_ext: Clean up and standardize #if/#else/#endif markers in
>     sched/ext.c
>   sched_ext: Clean up and standardize #if/#else/#endif markers in
>     sched/ext.h
>   sched_ext: Clean up and standardize #if/#else/#endif markers in
>     sched/ext_idle.c
>   sched_ext: Clean up and standardize #if/#else/#endif markers in
>     sched/ext_idle.h

Applied with subject line update. Patch 3 left a stray #else block causing a
build failure. Will post the updated patch as a reply to the patch. For this
sort of changes, please at least do build testing.

Thanks.

-- 
tejun

Re: [PATCH 3/4] sched_ext: Clean up and standardize #if/#else/#endif markers in sched/ext_idle.c

[Tejun Heo]

The following is the updated version that got applied to sched_ext/for-6.17.

Thanks.
------ 8< ------
From 8834ace4a86db0a85cb003c2efd98e6a4389243c Mon Sep 17 00:00:00 2001
From: Cheng-Yang Chou <yphbchou0911@gmail.com>
Date: Wed, 11 Jun 2025 21:54:03 +0800
Subject: [PATCH] sched_ext: Always use SMP versions in kernel/sched/ext_idle.c

Simplify the scheduler by making formerly SMP-only primitives and data
structures unconditional.

tj: Updated subject for clarity. Fixed stray #else block which wasn't
    removed causing build failure.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext_idle.c | 35 +----------------------------------
 1 file changed, 1 insertion(+), 34 deletions(-)

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index 17802693e304..b79cbdb7999a 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -17,7 +17,6 @@ static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_enabled);
 /* Enable/disable per-node idle cpumasks */
 static DEFINE_STATIC_KEY_FALSE(scx_builtin_idle_per_node);
 
-#ifdef CONFIG_SMP
 /* Enable/disable LLC aware optimizations */
 static DEFINE_STATIC_KEY_FALSE(scx_selcpu_topo_llc);
 
@@ -794,17 +793,6 @@ static void reset_idle_masks(struct sched_ext_ops *ops)
 		cpumask_and(idle_cpumask(node)->smt, cpu_online_mask, node_mask);
 	}
 }
-#else	/* !CONFIG_SMP */
-static bool scx_idle_test_and_clear_cpu(int cpu)
-{
-	return -EBUSY;
-}
-
-static s32 scx_pick_idle_cpu(const struct cpumask *cpus_allowed, int node, u64 flags)
-{
-	return -EBUSY;
-}
-#endif	/* CONFIG_SMP */
 
 void scx_idle_enable(struct sched_ext_ops *ops)
 {
@@ -818,9 +806,7 @@ void scx_idle_enable(struct sched_ext_ops *ops)
 	else
 		static_branch_disable_cpuslocked(&scx_builtin_idle_per_node);
 
-#ifdef CONFIG_SMP
 	reset_idle_masks(ops);
-#endif
 }
 
 void scx_idle_disable(void)
@@ -906,7 +892,6 @@ static s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_f
 	if (!rq)
 		lockdep_assert_held(&p->pi_lock);
 
-#ifdef CONFIG_SMP
 	/*
 	 * This may also be called from ops.enqueue(), so we need to handle
 	 * per-CPU tasks as well. For these tasks, we can skip all idle CPU
@@ -923,9 +908,7 @@ static s32 select_cpu_from_kfunc(struct task_struct *p, s32 prev_cpu, u64 wake_f
 		cpu = scx_select_cpu_dfl(p, prev_cpu, wake_flags,
 					 allowed ?: p->cpus_ptr, flags);
 	}
-#else
-	cpu = -EBUSY;
-#endif
+
 	if (scx_kf_allowed_if_unlocked())
 		task_rq_unlock(rq, p, &rf);
 
@@ -1016,11 +999,7 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask_node(int node)
 	if (node < 0)
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	return idle_cpumask(node)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1040,11 +1019,7 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_cpumask(void)
 	if (!check_builtin_idle_enabled())
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	return idle_cpumask(NUMA_NO_NODE)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1063,14 +1038,10 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask_node(int node)
 	if (node < 0)
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	if (sched_smt_active())
 		return idle_cpumask(node)->smt;
 	else
 		return idle_cpumask(node)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
@@ -1091,14 +1062,10 @@ __bpf_kfunc const struct cpumask *scx_bpf_get_idle_smtmask(void)
 	if (!check_builtin_idle_enabled())
 		return cpu_none_mask;
 
-#ifdef CONFIG_SMP
 	if (sched_smt_active())
 		return idle_cpumask(NUMA_NO_NODE)->smt;
 	else
 		return idle_cpumask(NUMA_NO_NODE)->cpu;
-#else
-	return cpu_none_mask;
-#endif
 }
 
 /**
-- 
2.49.0

Re: [PATCH 0/4] sched_ext: Standardize preprocessor comment markers

[Cheng-Yang Chou]

On Fri, Jun 13, 2025 at 02:42:06PM -1000, Tejun Heo wrote:
> Applied with subject line update. Patch 3 left a stray #else block causing a
> build failure. Will post the updated patch as a reply to the patch. For this
> sort of changes, please at least do build testing.

Thanks for pointing that out and for fixing it.

-chengyang