linux-kernel - [RFC PATCH 30/86] Revert "preempt: Introduce CONFIG_PREEMPT

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Message-Id: <20231107215742.363031-31-ankur.a.arora@oracle.com>
Date:   Tue,  7 Nov 2023 13:57:16 -0800
From:   Ankur Arora <ankur.a.arora@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org,
        torvalds@...ux-foundation.org, paulmck@...nel.org,
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        Ankur Arora <ankur.a.arora@...cle.com>
Subject: [RFC PATCH 30/86] Revert "preempt: Introduce CONFIG_PREEMPT_DYNAMIC"

This reverts commit 6ef869e0647439af0fc28dde162d33320d4e1dd7.

Also remove the CONFIG_PREEMPT_DYNAMIC guarded inclusion of
linux/entry-common.h which seems to have been missed somewhere.

Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
 .../admin-guide/kernel-parameters.txt         |  7 -------
 arch/Kconfig                                  |  9 ---------
 arch/x86/Kconfig                              |  1 -
 kernel/Kconfig.preempt                        | 19 -------------------
 kernel/sched/core.c                           |  6 ------
 5 files changed, 42 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0a1731a0f0ef..93b60558a78f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4577,13 +4577,6 @@
 			Format: {"off"}
 			Disable Hardware Transactional Memory
 
-	preempt=	[KNL]
-			Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC
-			none - Limited to cond_resched() calls
-			voluntary - Limited to cond_resched() and might_sleep() calls
-			full - Any section that isn't explicitly preempt disabled
-			       can be preempted anytime.
-
 	print-fatal-signals=
 			[KNL] debug: print fatal signals
 
diff --git a/arch/Kconfig b/arch/Kconfig
index afe6785fd3e2..05ce60036ecc 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -1393,15 +1393,6 @@ config HAVE_STATIC_CALL_INLINE
 	depends on HAVE_STATIC_CALL
 	select OBJTOOL
 
-config HAVE_PREEMPT_DYNAMIC
-	bool
-	depends on HAVE_STATIC_CALL
-	depends on GENERIC_ENTRY
-	help
-	  Select this if the architecture support boot time preempt setting
-	  on top of static calls. It is strongly advised to support inline
-	  static call to avoid any overhead.
-
 config ARCH_WANT_LD_ORPHAN_WARN
 	bool
 	help
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ec71c232af32..76e418bf469d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -270,7 +270,6 @@ config X86
 	select HAVE_STACK_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_STATIC_CALL
 	select HAVE_STATIC_CALL_INLINE		if HAVE_OBJTOOL
-	select HAVE_PREEMPT_DYNAMIC
 	select HAVE_RSEQ
 	select HAVE_RUST			if X86_64
 	select HAVE_SYSCALL_TRACEPOINTS
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 5876e30c5740..715e7aebb9d8 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -40,7 +40,6 @@ config PREEMPT
 	depends on !ARCH_NO_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)
@@ -82,24 +81,6 @@ config PREEMPTION
        bool
        select PREEMPT_COUNT
 
-config PREEMPT_DYNAMIC
-	bool
-	help
-	  This option allows to define the preemption model on the kernel
-	  command line parameter and thus override the default preemption
-	  model defined during compile time.
-
-	  The feature is primarily interesting for Linux distributions which
-	  provide a pre-built kernel binary to reduce the number of kernel
-	  flavors they offer while still offering different usecases.
-
-	  The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
-	  but if runtime patching is not available for the specific architecture
-	  then the potential overhead should be considered.
-
-	  Interesting if you want the same pre-built kernel should be used for
-	  both Server and Desktop workloads.
-
 config SCHED_CORE
 	bool "Core Scheduling for SMT"
 	depends on SCHED_SMT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5a0bf43975d4..e30007c11722 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -65,12 +65,6 @@
 #include <linux/wait_api.h>
 #include <linux/workqueue_api.h>
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
-# ifdef CONFIG_GENERIC_ENTRY
-#  include <linux/entry-common.h>
-# endif
-#endif
-
 #include <uapi/linux/sched/types.h>
 
 #include <asm/irq_regs.h>
-- 
2.31.1