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Message-Id: <20211109151057.3489223-1-valentin.schneider@arm.com>
Date: Tue, 9 Nov 2021 15:10:57 +0000
From: Valentin Schneider <valentin.schneider@....com>
To: linux-kernel@...r.kernel.org
Cc: Mike Galbraith <efault@....de>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH] sched: Split preemption model selection between DYNAMIC & !DYNAMIC
From: Mike Galbraith <efault@....de>
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, split the preemption
model selection based on PREEMPT_DYNAMIC. !PREEMPT_DYNAMIC reverts to the
old behaviour with CONFIG_PREEMPT & friends being the user-visible config,
while PREEMPT_DYNAMIC exposes the _BEHAVIOUR counterparts.
Signed-off-by: Mike Galbraith <efault@....de>
[Changelog; deduplicated some config logic]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
kernel/Kconfig.preempt | 80 +++++++++++++++++++++++-------------------
1 file changed, 43 insertions(+), 37 deletions(-)
diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 60f1bfc3c7b2..4e60afae248e 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,12 +1,32 @@
# SPDX-License-Identifier: GPL-2.0-only
+config PREEMPT_DYNAMIC
+ bool "Preemption behaviour defined on boot"
+ depends on HAVE_PREEMPT_DYNAMIC && !ARCH_NO_PREEMPT
+ select PREEMPT
+ help
+ This option allows to define the preemption model on the kernel
+ command line parameter and thus override the default preemption
+ model defined during compile time.
+
+ The feature is primarily interesting for Linux distributions which
+ provide a pre-built kernel binary to reduce the number of kernel
+ flavors they offer while still offering different usecases.
+
+ The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
+ but if runtime patching is not available for the specific architecture
+ then the potential overhead should be considered.
+
+ Interesting if you want the same pre-built kernel should be used for
+ both Server and Desktop workloads.
+
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
+ depends on !PREEMPT_DYNAMIC
help
This is the traditional Linux preemption model, geared towards
throughput. It will still provide good latencies most of the
@@ -18,10 +38,9 @@ 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
+ depends on !ARCH_NO_PREEMPT && !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 +56,11 @@ 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 PREEMPTION
+ select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
help
This option reduces the latency of the kernel by making
all kernel code (that is not executing in a critical section)
@@ -75,16 +95,23 @@ config PREEMPT_RT
endchoice
-config PREEMPT_NONE
- bool
+choice
+ prompt "Default boot-time Preemption Model"
+ depends on PREEMPT_DYNAMIC
+ default PREEMPT_NONE_BEHAVIOUR
+ help
+ This option defines the default preemption model of the kernel
+ if it hasn't been specified by the "preempt=" command line parameter.
-config PREEMPT_VOLUNTARY
- bool
+config PREEMPT_NONE_BEHAVIOUR
+ bool "No Forced Preemption (Server)"
-config PREEMPT
- bool
- select PREEMPTION
- select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
+config PREEMPT_VOLUNTARY_BEHAVIOUR
+ bool "Voluntary Kernel Preemption (Desktop)"
+
+config PREEMPT_BEHAVIOUR
+ bool "Preemptible Kernel (Low-Latency Desktop)"
+endchoice
config PREEMPT_COUNT
bool
@@ -93,27 +120,6 @@ config PREEMPTION
bool
select PREEMPT_COUNT
-config PREEMPT_DYNAMIC
- bool "Preemption behaviour defined on boot"
- depends on HAVE_PREEMPT_DYNAMIC
- select PREEMPT
- default y
- help
- This option allows to define the preemption model on the kernel
- command line parameter and thus override the default preemption
- model defined during compile time.
-
- The feature is primarily interesting for Linux distributions which
- provide a pre-built kernel binary to reduce the number of kernel
- flavors they offer while still offering different usecases.
-
- The runtime overhead is negligible with HAVE_STATIC_CALL_INLINE enabled
- but if runtime patching is not available for the specific architecture
- then the potential overhead should be considered.
-
- Interesting if you want the same pre-built kernel should be used for
- both Server and Desktop workloads.
-
config SCHED_CORE
bool "Core Scheduling for SMT"
depends on SCHED_SMT
--
2.25.1
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