sched/rt, 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 <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
Acked-by: Clark Williams <[email protected]>
Acked-by: Daniel Bristot de Oliveira <[email protected]>
Acked-by: Frederic Weisbecker <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
Acked-by: Daniel Wagner <[email protected]>
Acked-by: Luis Claudio R. Goncalves <[email protected]>
Acked-by: Julia Cartwright <[email protected]>
Acked-by: Tom Zanussi <[email protected]>
Acked-by: Gratian Crisan <[email protected]>
Acked-by: Sebastian Siewior <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Lukas Bulwahn <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Tejun Heo <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: KAGA-KOKO

arch/Kconfig

@@ -801,6 +801,9 @@ config ARCH_NO_COHERENT_DMA_MMAP
 config ARCH_NO_PREEMPT
 	bool
 
+config ARCH_SUPPORTS_RT
+	bool
+
 config CPU_NO_EFFICIENT_FFS
 	def_bool n
 

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-preemptible sections. This makes the kernel, except for very
+	  low level and critical code pathes (entry code, scheduler, low
+	  level interrupt handling) fully preemptible 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