Commit a8b76910 authored by Valentin Schneider's avatar Valentin Schneider Committed by Peter Zijlstra
Browse files

preempt: Restore preemption model selection configs 



Commit c597bfdd ("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: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarMarco Elver <elver@google.com>
Link: https://lore.kernel.org/r/20211110202448.4054153-2-valentin.schneider@arm.com
parent 4cc4cc28

include/linux/kernel.h

+1 −1
Original line number Diff line number Diff line
@@ -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()

include/linux/vermagic.h

+1 −1
Original line number Diff line number Diff line
@@ -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 "

init/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

kernel/Kconfig.preempt

+21 −21
Original line number Diff line number Diff line 
# 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

kernel/sched/core.c

+3 −3
Original line number Diff line number Diff line
@@ -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");

		}