1 files changed, 22 insertions, 4 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 2de5b1cbadd9..a619a1ac7f4c 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -340,6 +340,7 @@ choice
 
 config TREE_RCU
         bool "Tree-based hierarchical RCU"
+        depends on !PREEMPT && SMP
         help
           This option selects the RCU implementation that is
           designed for very large SMP system with hundreds or
@@ -347,7 +348,7 @@ config TREE_RCU
           smaller systems.
 
 config TREE_PREEMPT_RCU
-        bool "Preemptable tree-based hierarchical RCU"
+        bool "Preemptible tree-based hierarchical RCU"
         depends on PREEMPT
         help
           This option selects the RCU implementation that is
@@ -365,8 +366,22 @@ config TINY_RCU
           is not required.  This option greatly reduces the
           memory footprint of RCU.
 
+config TINY_PREEMPT_RCU
+        bool "Preemptible UP-only small-memory-footprint RCU"
+        depends on !SMP && PREEMPT
+        help
+          This option selects the RCU implementation that is designed
+          for real-time UP systems.  This option greatly reduces the
+          memory footprint of RCU.
+
 endchoice
 
+config PREEMPT_RCU
+        def_bool ( TREE_PREEMPT_RCU || TINY_PREEMPT_RCU )
+        help
+          This option enables preemptible-RCU code that is common between
+          the TREE_PREEMPT_RCU and TINY_PREEMPT_RCU implementations.
+
 config RCU_TRACE
         bool "Enable tracing for RCU"
         depends on TREE_RCU || TREE_PREEMPT_RCU
@@ -387,9 +402,12 @@ config RCU_FANOUT
         help
           This option controls the fanout of hierarchical implementations
           of RCU, allowing RCU to work efficiently on machines with
-          large numbers of CPUs.  This value must be at least the cube
-          root of NR_CPUS, which allows NR_CPUS up to 32,768 for 32-bit
-          systems and up to 262,144 for 64-bit systems.
+          large numbers of CPUs.  This value must be at least the fourth
+          root of NR_CPUS, which allows NR_CPUS to be insanely large.
+          The default value of RCU_FANOUT should be used for production
+          systems, but if you are stress-testing the RCU implementation
+          itself, small RCU_FANOUT values allow you to test large-system
+          code paths on small(er) systems.
 
           Select a specific number if testing RCU itself.
           Take the default if unsure.