[RFC PATCH 16/86] Revert "sched: Provide Kconfig support for default dynamic preempt mode"

[Ankur Arora]

This reverts commit c597bfddc9e9e8a63817252b67c3ca0e544ace26.

Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
 kernel/Kconfig.preempt | 32 +++++++++-----------------------
 kernel/sched/core.c    | 29 +++--------------------------
 2 files changed, 12 insertions(+), 49 deletions(-)

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 60f1bfc3c7b2..5876e30c5740 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -2,11 +2,10 @@
 
 choice
 	prompt "Preemption Model"
-	default PREEMPT_NONE_BEHAVIOUR
+	default PREEMPT_NONE
 
-config PREEMPT_NONE_BEHAVIOUR
+config PREEMPT_NONE
 	bool "No Forced Preemption (Server)"
-	select PREEMPT_NONE if !PREEMPT_DYNAMIC
 	help
 	  This is the traditional Linux preemption model, geared towards
 	  throughput. It will still provide good latencies most of the
@@ -18,10 +17,9 @@ config PREEMPT_NONE_BEHAVIOUR
 	  raw processing power of the kernel, irrespective of scheduling
 	  latencies.
 
-config PREEMPT_VOLUNTARY_BEHAVIOUR
+config PREEMPT_VOLUNTARY
 	bool "Voluntary Kernel Preemption (Desktop)"
 	depends on !ARCH_NO_PREEMPT
-	select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC
 	help
 	  This option reduces the latency of the kernel by adding more
 	  "explicit preemption points" to the kernel code. These new
@@ -37,10 +35,12 @@ config PREEMPT_VOLUNTARY_BEHAVIOUR
 
 	  Select this if you are building a kernel for a desktop system.
 
-config PREEMPT_BEHAVIOUR
+config PREEMPT
 	bool "Preemptible Kernel (Low-Latency Desktop)"
 	depends on !ARCH_NO_PREEMPT
-	select PREEMPT
+	select PREEMPTION
+	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
+	select PREEMPT_DYNAMIC if HAVE_PREEMPT_DYNAMIC
 	help
 	  This option reduces the latency of the kernel by making
 	  all kernel code (that is not executing in a critical section)
@@ -58,7 +58,7 @@ config PREEMPT_BEHAVIOUR
 
 config PREEMPT_RT
 	bool "Fully Preemptible Kernel (Real-Time)"
-	depends on EXPERT && ARCH_SUPPORTS_RT && !PREEMPT_DYNAMIC
+	depends on EXPERT && ARCH_SUPPORTS_RT
 	select PREEMPTION
 	help
 	  This option turns the kernel into a real-time kernel by replacing
@@ -75,17 +75,6 @@ config PREEMPT_RT
 
 endchoice
 
-config PREEMPT_NONE
-	bool
-
-config PREEMPT_VOLUNTARY
-	bool
-
-config PREEMPT
-	bool
-	select PREEMPTION
-	select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
-
 config PREEMPT_COUNT
        bool
 
@@ -94,10 +83,7 @@ config PREEMPTION
        select PREEMPT_COUNT
 
 config PREEMPT_DYNAMIC
-	bool "Preemption behaviour defined on boot"
-	depends on HAVE_PREEMPT_DYNAMIC
-	select PREEMPT
-	default y
+	bool
 	help
 	  This option allows to define the preemption model on the kernel
 	  command line parameter and thus override the default preemption
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d3828d90bf84..12f255e038ed 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6991,13 +6991,12 @@ EXPORT_STATIC_CALL_TRAMP(preempt_schedule_notrace);
  */
 
 enum {
-	preempt_dynamic_undefined = -1,
-	preempt_dynamic_none,
+	preempt_dynamic_none = 0,
 	preempt_dynamic_voluntary,
 	preempt_dynamic_full,
 };
 
-int preempt_dynamic_mode = preempt_dynamic_undefined;
+int preempt_dynamic_mode = preempt_dynamic_full;
 
 int sched_dynamic_mode(const char *str)
 {
@@ -7070,27 +7069,7 @@ static int __init setup_preempt_mode(char *str)
 }
 __setup("preempt=", setup_preempt_mode);
 
-static void __init preempt_dynamic_init(void)
-{
-	if (preempt_dynamic_mode == preempt_dynamic_undefined) {
-		if (IS_ENABLED(CONFIG_PREEMPT_NONE_BEHAVIOUR)) {
-			sched_dynamic_update(preempt_dynamic_none);
-		} else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY_BEHAVIOUR)) {
-			sched_dynamic_update(preempt_dynamic_voluntary);
-		} else {
-			/* Default static call setting, nothing to do */
-			WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_BEHAVIOUR));
-			preempt_dynamic_mode = preempt_dynamic_full;
-			pr_info("Dynamic Preempt: full\n");
-		}
-	}
-}
-
-#else /* !CONFIG_PREEMPT_DYNAMIC */
-
-static inline void preempt_dynamic_init(void) { }
-
-#endif /* #ifdef CONFIG_PREEMPT_DYNAMIC */
+#endif /* CONFIG_PREEMPT_DYNAMIC */
 
 /*
  * This is the entry point to schedule() from kernel preemption
@@ -9966,8 +9945,6 @@ void __init sched_init(void)
 
 	init_uclamp();
 
-	preempt_dynamic_init();
-
 	scheduler_running = 1;
 }
 
-- 
2.31.1