rcu: Advise most users not to enable RCU user mode
Discourage distros from enabling CONFIG_RCU_USER_QS
because it brings overhead for no benefits yet.
It's not a useful feature on its own until we can
fully run an adaptive tickless kernel.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/init/Kconfig b/init/Kconfig
index c26b8a1d..89093e1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -451,6 +451,12 @@
excluded from the global RCU state machine and thus doesn't
to keep the timer tick on for RCU.
+ Unless you want to hack and help the development of the full
+ tickless feature, you shouldn't enable this option. It adds
+ unnecessary overhead.
+
+ If unsure say N
+
config RCU_USER_QS_FORCE
bool "Force userspace extended QS by default"
depends on RCU_USER_QS
@@ -459,6 +465,12 @@
test this feature that treats userspace as an extended quiescent
state until we have a real user like a full adaptive nohz option.
+ Unless you want to hack and help the development of the full
+ tickless feature, you shouldn't enable this option. It adds
+ unnecessary overhead.
+
+ If unsure say N
+
config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT