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

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Message-ID: <20150422143003.GX5561@linux.vnet.ibm.com>
Date:	Wed, 22 Apr 2015 07:30:03 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Pranith Kumar <bobby.prani@...il.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 Wed, Apr 22, 2015 at 01:22:23AM -0400, Pranith Kumar wrote:
> 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...

Good catch, fixes to delete the two added "default" statements.
The default thus is now 16, as it was before.

							Thanx, Paul

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