linux-kernel - Re: [PATCH tip/core/rcu 09/12] rcu: Break dependency of RCU_FANOUT_LEAF on RCU

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Date:	Wed, 22 Apr 2015 01:22:23 -0400
From:	Pranith Kumar <bobby.prani@...il.com>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH tip/core/rcu 09/12] rcu: Break dependency of
 RCU_FANOUT_LEAF on RCU_FANOUT

On Tue, Apr 21, 2015 at 3:55 PM, Paul E. McKenney
<paulmck@...ux.vnet.ibm.com> wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
>
> RCU_FANOUT_LEAF's range and default values depend on the value of
> RCU_FANOUT, which at the time seemed like a cute way to save two lines
> of Kconfig code.  However, adding a dependency from both of these
> Kconfig parameters on RCU_EXPERT requires that RCU_FANOUT_LEAF operate
> correctly even if RCU_FANOUT is undefined.  This commit therefore
> allows RCU_FANOUT_LEAF to take on the full range of permitted values,
> even in cases where RCU_FANOUT is undefined.
>
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> ---
>  init/Kconfig | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/init/Kconfig b/init/Kconfig
> index aa68d72fe051..35559e07db18 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -599,9 +599,11 @@ config RCU_FANOUT
>
>  config RCU_FANOUT_LEAF
>         int "Tree-based hierarchical RCU leaf-level fanout value"
> -       range 2 RCU_FANOUT if 64BIT
> -       range 2 RCU_FANOUT if !64BIT
> +       range 2 64 if 64BIT
> +       range 2 32 if !64BIT
>         depends on TREE_RCU || PREEMPT_RCU
> +       default 64 if 64BIT
> +       default 32 if !64BIT
>         default 16

What is the effect of this 'default 16' line? It is either 64 or 32
based on 64BIT, not sure when it is 16...

>         help
>           This option controls the leaf-level fanout of hierarchical
> --
> 1.8.1.5
>



-- 
Pranith
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