preempt: Restore preemption model selection configs

Commit f1cfd26742ec ("sched: Provide Kconfig support for default dynamic
preempt mode") changed the selectable config names for the preemption
model. This means a config file must now select

  CONFIG_PREEMPT_BEHAVIOUR=y

rather than

  CONFIG_PREEMPT=y

to get a preemptible kernel. This means all arch config files would need to
be updated - right now they'll all end up with the default
CONFIG_PREEMPT_NONE_BEHAVIOUR.

Rather than touch a good hundred of config files, restore usage of
CONFIG_PREEMPT{_NONE, _VOLUNTARY}. Make them configure:
o The build-time preemption model when !PREEMPT_DYNAMIC
o The default boot-time preemption model when PREEMPT_DYNAMIC

Add siblings of those configs with the _BUILD suffix to unconditionally
designate the build-time preemption model (PREEMPT_DYNAMIC is built with
the "highest" preemption model it supports, aka PREEMPT). Downstream
configs should by now all be depending / selected by CONFIG_PREEMPTION
rather than CONFIG_PREEMPT, so only a few sites need patching up.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20211110202448.4054153-2-valentin.schneider@arm.com

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 968b4c4fe65b7b563b763eefdd1b5219998272a2..77755ac3e189bfa23255bbba4e5c48f4fd8a65f2 100644 (file)
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -85,7 +85,7 @@
 struct completion;
 struct user;
 
-#ifdef CONFIG_PREEMPT_VOLUNTARY
+#ifdef CONFIG_PREEMPT_VOLUNTARY_BUILD
 
 extern int __cond_resched(void);
 # define might_resched() __cond_resched()

diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index 1eaaa93c37bff4cf5d17888732c74983b58a0dc6..329d63babaeb80fd4a7abbbfb17861c0fcf8914b 100644 (file)
--- a/include/linux/vermagic.h
+++ b/include/linux/vermagic.h
@@ -15,7 +15,7 @@
 #else
 #define MODULE_VERMAGIC_SMP ""
 #endif
-#ifdef CONFIG_PREEMPT
+#ifdef CONFIG_PREEMPT_BUILD
 #define MODULE_VERMAGIC_PREEMPT "preempt "
 #elif defined(CONFIG_PREEMPT_RT)
 #define MODULE_VERMAGIC_PREEMPT "preempt_rt "

diff --git a/init/Makefile b/init/Makefile
index 2846113677ee6241c267ded1eb59e39486c27f74..04eeee12c076d16547de30de1d283a2cddae1115 100644 (file)
--- a/init/Makefile
+++ b/init/Makefile
@@ -30,7 +30,7 @@ $(obj)/version.o: include/generated/compile.h
 quiet_cmd_compile.h = CHK     $@
       cmd_compile.h = \
        $(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@       \
-       "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT)"    \
+       "$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT_BUILD)"      \
        "$(CONFIG_PREEMPT_RT)" $(CONFIG_CC_VERSION_TEXT) "$(LD)"
 
 include/generated/compile.h: FORCE

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 60f1bfc3c7b246df3b6fc9d0381e6802471a59ed..ce77f02656603d473ae0091a365f22061be3acc0 100644 (file)
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,12 +1,23 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+config PREEMPT_NONE_BUILD
+       bool
+
+config PREEMPT_VOLUNTARY_BUILD
+       bool
+
+config PREEMPT_BUILD
+       bool
+       select PREEMPTION
+       select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
+
 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
+       select PREEMPT_NONE_BUILD 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 +29,10 @@ 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
+       select PREEMPT_VOLUNTARY_BUILD 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 +48,10 @@ 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 PREEMPT_BUILD
        help
          This option reduces the latency of the kernel by making
          all kernel code (that is not executing in a critical section)
@@ -58,7 +69,7 @@ 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 +86,6 @@ 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
 
@@ -95,8 +95,8 @@ config PREEMPTION
 
 config PREEMPT_DYNAMIC
        bool "Preemption behaviour defined on boot"
-       depends on HAVE_PREEMPT_DYNAMIC
-       select PREEMPT
+       depends on HAVE_PREEMPT_DYNAMIC && !PREEMPT_RT
+       select PREEMPT_BUILD
        default y
        help
          This option allows to define the preemption model on the kernel

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 862af1db22ab3b09e26778da56bd49da1488c056..3c9b0fda64ac08b00723227bad6203279d8a9b1b 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6628,13 +6628,13 @@ __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)) {
+               if (IS_ENABLED(CONFIG_PREEMPT_NONE)) {
                        sched_dynamic_update(preempt_dynamic_none);
-               } else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY_BEHAVIOUR)) {
+               } else if (IS_ENABLED(CONFIG_PREEMPT_VOLUNTARY)) {
                        sched_dynamic_update(preempt_dynamic_voluntary);
                } else {
                        /* Default static call setting, nothing to do */
-                       WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_BEHAVIOUR));
+                       WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT));
                        preempt_dynamic_mode = preempt_dynamic_full;
                        pr_info("Dynamic Preempt: full\n");
                }