2 files changed, 94 insertions, 3 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 8e9904fc3024..f6281711166d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -945,10 +945,90 @@ source "block/Kconfig"
 config PREEMPT_NOTIFIERS
         bool
 
+choice
+        prompt "RCU Implementation"
+        default CLASSIC_RCU
+
 config CLASSIC_RCU
-        def_bool !PREEMPT_RCU
+        bool "Classic RCU"
         help
           This option selects the classic RCU implementation that is
           designed for best read-side performance on non-realtime
-          systems.  Classic RCU is the default.  Note that the
-          PREEMPT_RCU symbol is used to select/deselect this option.
+          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
+        help
+          This option reduces the latency of the kernel by making certain
+          RCU sections preemptible. Normally RCU code is non-preemptible, if
+          this option is selected then read-only RCU sections become
+          preemptible. This helps latency, but may expose bugs due to
+          now-naive assumptions about each RCU read-side critical section
+          remaining on a given CPU through its execution.
+
+endchoice
+
+config RCU_TRACE
+        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.
+
+config TREE_RCU_TRACE
+        def_bool RCU_TRACE && TREE_RCU
+        select DEBUG_FS
+        help
+          This option provides tracing for the TREE_RCU implementation,
+          permitting Makefile to trivially select kernel/rcutree_trace.c.
+
+config PREEMPT_RCU_TRACE
+        def_bool RCU_TRACE && PREEMPT_RCU
+        select DEBUG_FS
+        help
+          This option provides tracing for the PREEMPT_RCU implementation,
+          permitting Makefile to trivially select kernel/rcupreempt_trace.c.
diff --git a/init/main.c b/init/main.c
index 17e9757bfde2..2a7ce0f8e453 100644
--- a/init/main.c
+++ b/init/main.c
@@ -540,6 +540,15 @@ void __init __weak thread_info_cache_init(void)
 {
 }
 
+void __init __weak arch_early_irq_init(void)
+{
+}
+
+void __init __weak early_irq_init(void)
+{
+        arch_early_irq_init();
+}
+
 asmlinkage void __init start_kernel(void)
 {
         char * command_line;
@@ -604,6 +613,8 @@ asmlinkage void __init start_kernel(void)
         sort_main_extable();
         trap_init();
         rcu_init();
+        /* init some links before init_ISA_irqs() */
+        early_irq_init();
         init_IRQ();
         pidhash_init();
         init_timers();