linux-kernel - Re: [PATCH] rcu: Advise most users not to enable RCU user mode

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Date:	Wed, 10 Oct 2012 17:50:04 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
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 <fweisbec@...il.com>
> ---
>  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
> 

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