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From: Ankur Arora <ankur.a.arora@oracle.com>
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        Ankur Arora <ankur.a.arora@oracle.com>
Subject: [PATCH 11/30] sched: runtime preemption config under PREEMPT_AUTO
Date: Mon, 12 Feb 2024 21:55:35 -0800
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Reuse sched_dynamic_update() and related logic to enable choosing
the preemption model at boot or runtime for PREEMPT_AUTO.

The interface is identical to PREEMPT_DYNAMIC.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 include/linux/sched.h |  2 +-
 kernel/sched/core.c   | 31 +++++++++++++++++++++++++++----
 kernel/sched/debug.c  |  6 +++---
 kernel/sched/sched.h  |  2 +-
 4 files changed, 32 insertions(+), 9 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d226c2920cff..58e6ea7572a0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2073,7 +2073,7 @@ extern int __cond_resched_rwlock_write(rwlock_t *lock);
 	__cond_resched_rwlock_write(lock);					\
 })
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) || defined(CONFIG_PREEMPT_AUTO)
 
 extern bool preempt_model_none(void);
 extern bool preempt_model_voluntary(void);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 6c5de6c1da27..e5d631197f35 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8692,9 +8692,13 @@ int __cond_resched_rwlock_write(rwlock_t *lock)
 }
 EXPORT_SYMBOL(__cond_resched_rwlock_write);
 
-#if defined(CONFIG_PREEMPT_DYNAMIC)
+#if defined(CONFIG_PREEMPT_DYNAMIC) || defined (CONFIG_PREEMPT_AUTO)
 
+#ifdef CONFIG_PREEMPT_DYNAMIC
 #define PREEMPT_MODE "Dynamic Preempt"
+#else
+#define PREEMPT_MODE "Preempt Auto"
+#endif
 
 enum {
 	preempt_dynamic_undefined = -1,
@@ -8769,11 +8773,11 @@ PREEMPT_MODEL_ACCESSOR(none);
 PREEMPT_MODEL_ACCESSOR(voluntary);
 PREEMPT_MODEL_ACCESSOR(full);
 
-#else /* !CONFIG_PREEMPT_DYNAMIC */
+#else /* !CONFIG_PREEMPT_DYNAMIC && !CONFIG_PREEMPT_AUTO */
 
 static inline void preempt_dynamic_init(void) { }
 
-#endif /* !CONFIG_PREEMPT_DYNAMIC */
+#endif /* !CONFIG_PREEMPT_DYNAMIC && !CONFIG_PREEMPT_AUTO */
 
 #ifdef CONFIG_PREEMPT_DYNAMIC
 
@@ -8904,7 +8908,26 @@ void sched_dynamic_klp_disable(void)
 
 #endif /* CONFIG_HAVE_PREEMPT_DYNAMIC_CALL */
 
-#endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
+#elif defined(CONFIG_PREEMPT_AUTO)
+
+static void __sched_dynamic_update(int mode)
+{
+	switch (mode) {
+	case preempt_dynamic_none:
+		preempt_dynamic_mode = preempt_dynamic_undefined;
+		break;
+
+	case preempt_dynamic_voluntary:
+		preempt_dynamic_mode = preempt_dynamic_undefined;
+		break;
+
+	case preempt_dynamic_full:
+		preempt_dynamic_mode = preempt_dynamic_undefined;
+		break;
+	}
+}
+
+#endif /* CONFIG_PREEMPT_AUTO */
 
 /**
  * yield - yield the current processor to other threads.
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 8d5d98a5834d..e53f1b73bf4a 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -216,7 +216,7 @@ static const struct file_operations sched_scaling_fops = {
 
 #endif /* SMP */
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) || defined(CONFIG_PREEMPT_AUTO)
 
 static ssize_t sched_dynamic_write(struct file *filp, const char __user *ubuf,
 				   size_t cnt, loff_t *ppos)
@@ -276,7 +276,7 @@ static const struct file_operations sched_dynamic_fops = {
 	.release	= single_release,
 };
 
-#endif /* CONFIG_PREEMPT_DYNAMIC */
+#endif /* CONFIG_PREEMPT_DYNAMIC || CONFIG_PREEMPT_AUTO */
 
 __read_mostly bool sched_debug_verbose;
 
@@ -343,7 +343,7 @@ static __init int sched_init_debug(void)
 
 	debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
 	debugfs_create_file_unsafe("verbose", 0644, debugfs_sched, &sched_debug_verbose, &sched_verbose_fops);
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) || defined(CONFIG_PREEMPT_AUTO)
 	debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
 #endif
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 001fe047bd5d..34899d17553e 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -3229,7 +3229,7 @@ extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *w
 
 extern int try_to_wake_up(struct task_struct *tsk, unsigned int state, int wake_flags);
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_PREEMPT_DYNAMIC) || defined(CONFIG_PREEMPT_AUTO)
 extern int preempt_dynamic_mode;
 extern int sched_dynamic_mode(const char *str);
 extern void sched_dynamic_update(int mode);
-- 
2.31.1