2012-10-10 23:48:38

by Frederic Weisbecker

Subject: [PATCH] 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 <[email protected]>
---
init/Kconfig | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index c26b8a1..89093e1 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -451,6 +451,12 @@ config RCU_USER_QS
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 @@ config RCU_USER_QS_FORCE
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
--
1.7.5.4

2012-10-11 00:50:11

by Paul E. McKenney

Subject: Re: [PATCH] rcu: Advise most users not to enable RCU user mode

On Thu, Oct 11, 2012 at 01:48:28AM +0200, Frederic Weisbecker wrote:
> 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.

Queued, hopefully for 3.7, thank you!

Thanx, Paul

> Signed-off-by: Frederic Weisbecker <[email protected]>
> ---
> init/Kconfig | 12 ++++++++++++
> 1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index c26b8a1..89093e1 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -451,6 +451,12 @@ config RCU_USER_QS
> 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 @@ config RCU_USER_QS_FORCE
> 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
> --
> 1.7.5.4
>