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preempt: Restore preemption model selection configs

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Commit c597bfddc9 ("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
This commit is contained in:
Valentin Schneider 2021-11-10 20:24:44 +00:00 committed by Peter Zijlstra
parent 4cc4cc28ec
commit a8b76910e4
5 changed files with 27 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/kernel.h
View File

@ -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()

2
include/linux/vermagic.h
View File

@ -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 "

2
init/Makefile
View File

@ -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

42
kernel/Kconfig.preempt
View File

@ -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

6
kernel/sched/core.c
View File

@ -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");
}