linux-kernel - [PATCH] sched: Tweak default dynamic preempt mode selection

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Message-Id: <20211105104035.3112162-1-valentin.schneider@arm.com>
Date:   Fri,  5 Nov 2021 10:40:35 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>
Subject: [PATCH] sched: Tweak default dynamic preempt mode selection

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 need to be
updated - right now arm64 defconfig selects CONFIG_PREEMPT=y but ends up
with CONFIG_PREEMPT_NONE_BEHAVIOUR=y.

Instead, have CONFIG_*PREEMPT be the selectable configs again, and make
them select their _BEHAVIOUR equivalent if CONFIG_PREEMPT_DYNAMIC is set.

Signed-off-by: Valentin Schneider <valentin.schneider@....com>
---
 kernel/Kconfig.preempt | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 60f1bfc3c7b2..25e8d6a3d9fa 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -1,12 +1,21 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+config PREEMPT_NONE_BEHAVIOUR
+	bool
+
+config PREEMPT_VOLUNTARY_BEHAVIOUR
+	bool
+
+config PREEMPT_BEHAVIOUR
+	bool
+
 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_BEHAVIOUR 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 +27,10 @@ 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_BEHAVIOUR 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 +46,12 @@ 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
+	select PREEMPT_BEHAVIOUR if PREEMPT_DYNAMIC
 	help
 	  This option reduces the latency of the kernel by making
 	  all kernel code (that is not executing in a critical section)
@@ -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
 
-- 
2.25.1