linux-kernel - Re: [PATCH tip/core/rcu 11/12] rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT

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Message-ID: <20150422143054.GY5561@linux.vnet.ibm.com>
Date:	Wed, 22 Apr 2015 07:30:54 -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 11/12] rcu: Make RCU able to tolerate
 undefined CONFIG_RCU_FANOUT_LEAF

On Wed, Apr 22, 2015 at 01:25:07AM -0400, Pranith Kumar wrote:
> On Tue, Apr 21, 2015 at 3:55 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
> > index 2e52502bfc95..a2f64e4fdb57 100644
> > --- a/kernel/rcu/tree_plugin.h
> > +++ b/kernel/rcu/tree_plugin.h
> > @@ -86,10 +86,10 @@ static void __init rcu_bootup_announce_oddness(void)
> >                 pr_info("\tAdditional per-CPU info printed with stalls.\n");
> >         if (RCU_NUM_LVLS >= 4)
> >                 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
> > -       if (CONFIG_RCU_FANOUT_LEAF != 16)
> > +       if (RCU_FANOUT_LEAF != 16)
> 
> So if CONFIG_RCU_FANOUT_LEAF is either by default 32 or 64, this check
> against 16 for build-time adjustment is a bit misleading, no?

Indeed!

However, with the fix that puts the default back to 16, this should be
once again correct.

							Thanx, Paul

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