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rcu: Advise most users not to enable RCU user mode

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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>
This commit is contained in:
Frederic Weisbecker 2012-10-11 01:48:28 +02:00 committed by Paul E. McKenney
parent a4fbe35a12
commit d677124b1f
1 changed files with 12 additions and 0 deletions
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12
init/Kconfig
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@ -451,6 +451,12 @@ config RCU_USER_QS
excluded from the global RCU state machine and thus doesn't excluded from the global RCU state machine and thus doesn't
to keep the timer tick on for RCU. 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 config RCU_USER_QS_FORCE
bool "Force userspace extended QS by default" bool "Force userspace extended QS by default"
depends on RCU_USER_QS depends on RCU_USER_QS
@ -459,6 +465,12 @@ config RCU_USER_QS_FORCE
test this feature that treats userspace as an extended quiescent test this feature that treats userspace as an extended quiescent
state until we have a real user like a full adaptive nohz option. 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 config RCU_FANOUT
int "Tree-based hierarchical RCU fanout value" int "Tree-based hierarchical RCU fanout value"
range 2 64 if 64BIT range 2 64 if 64BIT