On Wed, Nov 10, 2021 at 08:24PM +0000, Valentin Schneider wrote:
> Commit c597bfddc9e9 ("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@xxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Much better, thank you!
> ---
> include/linux/kernel.h | 2 +-
> include/linux/vermagic.h | 2 +-
> init/Makefile | 2 +-
> kernel/Kconfig.preempt | 42 ++++++++++++++++++++--------------------
> kernel/sched/core.c | 6 +++---
> 5 files changed, 27 insertions(+), 27 deletions(-)
>
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 2776423a587e..9c7d774ef809 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -88,7 +88,7 @@
> 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 1eaaa93c37bf..329d63babaeb 100644
> --- 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 2846113677ee..04eeee12c076 100644
> --- 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 60f1bfc3c7b2..ce77f0265660 100644
> --- 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 f2611b9cf503..97047aa7b6c2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6625,13 +6625,13 @@ __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");
> }
> --
> 2.25.1
>
