rcu: provide RCU options on non-preempt architectures too

Impact: build fix

Some old architectures still do not use kernel/Kconfig.preempt, so the
moving of the RCU options there broke their build:

 In file included from /home/mingo/tip/include/linux/sem.h:81,
                 from /home/mingo/tip/include/linux/sched.h:69,
                 from /home/mingo/tip/arch/alpha/kernel/asm-offsets.c:9:
 /home/mingo/tip/include/linux/rcupdate.h:62:2: error: #error "Unknown RCU implementation specified to kernel configuration"

Move these options back to init/Kconfig, which every architecture
includes.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 74 insertions, 0 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 9dd7958a71f0..6b0fdedf3596 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -928,6 +928,80 @@ source "block/Kconfig"
 config PREEMPT_NOTIFIERS
         bool
 
+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
+        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