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Subject[patch 1/1] Kconfig: Introduce CONFIG_PREEMPT_RT
Add a new entry to the preemption menu which enables the real-time support
for the kernel. The choice is only enabled when an architecture supports
it.

It selects PREEMPT as the RT features depend on it. To achieve that the
existing PREEMPT choice is renamed to PREEMPT_LL which select PREEMPT as
well.

No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/Kconfig | 3 +++
kernel/Kconfig.preempt | 25 +++++++++++++++++++++++--
2 files changed, 26 insertions(+), 2 deletions(-)

--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -809,6 +809,9 @@ config ARCH_NO_COHERENT_DMA_MMAP
config ARCH_NO_PREEMPT
bool

+config ARCH_SUPPORTS_RT
+ bool
+
config CPU_NO_EFFICIENT_FFS
def_bool n

--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -35,10 +35,10 @@ config PREEMPT_VOLUNTARY

Select this if you are building a kernel for a desktop system.

-config PREEMPT
+config PREEMPT_LL
bool "Preemptible Kernel (Low-Latency Desktop)"
depends on !ARCH_NO_PREEMPT
- select PREEMPT_COUNT
+ select PREEMPT
select UNINLINE_SPIN_UNLOCK if !ARCH_INLINE_SPIN_UNLOCK
help
This option reduces the latency of the kernel by making
@@ -55,7 +55,28 @@ config PREEMPT
embedded system with latency requirements in the milliseconds
range.

+config PREEMPT_RT
+ bool "Fully Preemptible Kernel (Real-Time)"
+ depends on EXPERT && ARCH_SUPPORTS_RT
+ select PREEMPT
+ help
+ This option turns the kernel into a real-time kernel by replacing
+ various locking primitives (spinlocks, rwlocks, etc) with
+ preemptible priority-inheritance aware variants, enforcing
+ interrupt threading and introducing mechanisms to break up long
+ non-preemtible sections. This makes the kernel, except for very
+ low level and critical code pathes (entry code, scheduler, low
+ level interrupt handling) fully preemtible and brings most
+ execution contexts under scheduler control.
+
+ Select this if you are building a kernel for systems which
+ require real-time guarantees.
+
endchoice

config PREEMPT_COUNT
bool
+
+config PREEMPT
+ bool
+ select PREEMPT_COUNT

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