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Message-ID: <87h7cks16n.mognet@arm.com>
Date: Wed, 10 Nov 2021 11:24:48 +0000
From: Valentin Schneider <valentin.schneider@....com>
To: Mike Galbraith <efault@....de>,
Frederic Weisbecker <frederic@...nel.org>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] sched: Split preemption model selection between DYNAMIC & !DYNAMIC
On 10/11/21 05:37, Mike Galbraith wrote:
> On Wed, 2021-11-10 at 02:17 +0100, Frederic Weisbecker wrote:
>> The problem here is that you're duplicating the existing titles
>> for the static entries and you're losing all the help that text that used to come
>> along. The point of the BEHAVIOUR thing, further mapping to either
>> static or dynamic preemption, was to avoid that duplication and keep the
>> same titles and help for the three behaviour, whether static or dynamic.
>
> Adding "depends on !PREEMPT_DYNAMIC" to the first (legacy?) choice made
> it appear/disappear at the appropriate time as well, but I have no idea
> how duplication of help text can be avoided.
>
> -Mike
Following Frederic's _STATIC suggestion, I got to the below. The nice thing
is if a defconfig picks say PREEMPT_VOLUNTARY and the arch supports
PREEMPT_DYNAMIC, then it'll pick PREEMPT_VOLUNTARY_BEHAVIOUR. The less nice
thing is that we end up selecting PREEMPT_STATIC for PREEMPT_DYNAMIC
kernels, naming's hard... Maybe _BUILD rather than _STATIC?
---
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 2776423a587e..1fa8f6fb3c55 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_STATIC
extern int __cond_resched(void);
# define might_resched() __cond_resched()
diff --git a/include/linux/vermagic.h b/include/linux/vermagic.h
index 1eaaa93c37bf..0a311d7aab62 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_STATIC
#define MODULE_VERMAGIC_PREEMPT "preempt "
#elif defined(CONFIG_PREEMPT_RT)
#define MODULE_VERMAGIC_PREEMPT "preempt_rt "
@@ -39,9 +39,9 @@
#define MODULE_RANDSTRUCT_PLUGIN
#endif
-#define VERMAGIC_STRING \
+#define VERMAGIC_STRING \
UTS_RELEASE " " \
- MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT \
+ MODULE_VERMAGIC_SMP MODULE_VERMAGIC_PREEMPT \
MODULE_VERMAGIC_MODULE_UNLOAD MODULE_VERMAGIC_MODVERSIONS \
MODULE_ARCH_VERMAGIC \
MODULE_RANDSTRUCT_PLUGIN
diff --git a/init/Makefile b/init/Makefile
index 2846113677ee..989f43d23b83 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)" "$(CONFIG_PREEMPT_STATIC)" \
"$(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..1761966c815e 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,12 +1,40 @@
# SPDX-License-Identifier: GPL-2.0-only
+
+choice
+ prompt "[Legacy compatibility] Preemption Model"
+
+config PREEMPT_NONE
+ bool "No Forced Preemption (Server)"
+
+config PREEMPT_VOLUNTARY
+ bool "Voluntary Kernel Preemption (Desktop)"
+
+config PREEMPT
+ bool "Preemptible Kernel (Low-Latency Desktop)"
+
+endchoice
+
+config PREEMPT_NONE_STATIC
+ bool
+
+config PREEMPT_VOLUNTARY_STATIC
+ bool
+
+config PREEMPT_STATIC
+ bool
+ select PREEMPTION
+ select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
+
choice
prompt "Preemption Model"
+ default PREEMPT_BEHAVIOUR if PREEMPT
+ default PREEMPT_VOLUNTARY_BEHAVIOUR if PREEMPT_VOLUNTARY
default PREEMPT_NONE_BEHAVIOUR
config PREEMPT_NONE_BEHAVIOUR
bool "No Forced Preemption (Server)"
- select PREEMPT_NONE if !PREEMPT_DYNAMIC
+ select PREEMPT_NONE_STATIC if !PREEMPT_DYNAMIC
help
This is the traditional Linux preemption model, geared towards
throughput. It will still provide good latencies most of the
@@ -21,7 +49,7 @@ config PREEMPT_NONE_BEHAVIOUR
config PREEMPT_VOLUNTARY_BEHAVIOUR
bool "Voluntary Kernel Preemption (Desktop)"
depends on !ARCH_NO_PREEMPT
- select PREEMPT_VOLUNTARY if !PREEMPT_DYNAMIC
+ select PREEMPT_VOLUNTARY_STATIC if !PREEMPT_DYNAMIC
help
This option reduces the latency of the kernel by adding more
"explicit preemption points" to the kernel code. These new
@@ -40,7 +68,7 @@ config PREEMPT_VOLUNTARY_BEHAVIOUR
config PREEMPT_BEHAVIOUR
bool "Preemptible Kernel (Low-Latency Desktop)"
depends on !ARCH_NO_PREEMPT
- select PREEMPT
+ select PREEMPT_STATIC
help
This option reduces the latency of the kernel by making
all kernel code (that is not executing in a critical section)
@@ -58,7 +86,7 @@ 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 +103,6 @@ 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 +112,8 @@ 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_STATIC
default y
help
This option allows to define the preemption model on the kernel
diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
index dc55fd5a36fc..83dd9e6a8235 100644
--- a/kernel/kcsan/kcsan_test.c
+++ b/kernel/kcsan/kcsan_test.c
@@ -1005,13 +1005,13 @@ static const void *nthreads_gen_params(const void *prev, char *desc)
else
nthreads *= 2;
- if (!IS_ENABLED(CONFIG_PREEMPT) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
+ if (!IS_ENABLED(CONFIG_PREEMPTION) || !IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER)) {
/*
* Without any preemption, keep 2 CPUs free for other tasks, one
* of which is the main test case function checking for
* completion or failure.
*/
- const long min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE) ? 2 : 0;
+ const long min_unused_cpus = IS_ENABLED(CONFIG_PREEMPT_NONE_STATIC) ? 2 : 0;
const long min_required_cpus = 2 + min_unused_cpus;
if (num_online_cpus() < min_required_cpus) {
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7896d30d90f7..67413be56f22 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4271,11 +4271,11 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
entries,
total,
buf->cpu,
-#if defined(CONFIG_PREEMPT_NONE)
+#if defined(CONFIG_PREEMPT_NONE_STATIC)
"server",
-#elif defined(CONFIG_PREEMPT_VOLUNTARY)
+#elif defined(CONFIG_PREEMPT_VOLUNTARY_STATIC)
"desktop",
-#elif defined(CONFIG_PREEMPT)
+#elif defined(CONFIG_PREEMPT_STATIC)
"preempt",
#elif defined(CONFIG_PREEMPT_RT)
"preempt_rt",
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