1 files changed, 56 insertions, 6 deletions

diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
index 9fdba03dc1fc..463f29743ea0 100644
--- a/kernel/Kconfig.preempt
+++ b/kernel/Kconfig.preempt
@@ -52,10 +52,29 @@ config PREEMPT
 
 endchoice
 
+choice
+        prompt "RCU Implementation"
+        default CLASSIC_RCU
+
+config CLASSIC_RCU
+        bool "Classic RCU"
+        help
+          This option selects the classic RCU implementation that is
+          designed for best read-side performance on non-realtime
+          systems.
+          
+          Select this option if you are unsure.
+
+config TREE_RCU
+        bool "Tree-based hierarchical RCU"
+        help
+          This option selects the RCU implementation that is
+          designed for very large SMP system with hundreds or
+          thousands of CPUs.
+
 config PREEMPT_RCU
         bool "Preemptible RCU"
         depends on PREEMPT
-        default n
         help
           This option reduces the latency of the kernel by making certain
           RCU sections preemptible. Normally RCU code is non-preemptible, if
@@ -64,16 +83,47 @@ config PREEMPT_RCU
           now-naive assumptions about each RCU read-side critical section
           remaining on a given CPU through its execution.
 
-          Say N if you are unsure.
+endchoice
 
 config RCU_TRACE
-        bool "Enable tracing for RCU - currently stats in debugfs"
-        depends on PREEMPT_RCU
-        select DEBUG_FS
-        default y
+        bool "Enable tracing for RCU"
+        depends on TREE_RCU || PREEMPT_RCU
         help
           This option provides tracing in RCU which presents stats
           in debugfs for debugging RCU implementation.
 
           Say Y here if you want to enable RCU tracing
           Say N if you are unsure.
+
+config RCU_FANOUT
+        int "Tree-based hierarchical RCU fanout value"
+        range 2 64 if 64BIT
+        range 2 32 if !64BIT
+        depends on TREE_RCU
+        default 64 if 64BIT
+        default 32 if !64BIT
+        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.
+
+          Select a specific number if testing RCU itself.
+          Take the default if unsure.
+
+config RCU_FANOUT_EXACT
+        bool "Disable tree-based hierarchical RCU auto-balancing"
+        depends on TREE_RCU
+        default n
+        help
+          This option forces use of the exact RCU_FANOUT value specified,
+          regardless of imbalances in the hierarchy.  This is useful for
+          testing RCU itself, and might one day be useful on systems with
+          strong NUMA behavior.
+
+          Without RCU_FANOUT_EXACT, the code will balance the hierarchy.
+
+          Say n if unsure.
+
+