linux-kernel - Re: [PATCH tip/core/rcu 01/22] rcu: Control RCU_FANOUT

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Date:	Sun, 1 Jul 2012 00:17:58 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	Rusty Russell <rusty@...abs.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org
Subject: Re: [PATCH tip/core/rcu 01/22] rcu: Control RCU_FANOUT_LEAF from
 boot-time parameter

On Sun, Jul 01, 2012 at 03:49:42PM +0930, Rusty Russell wrote:
> On Fri, 22 Jun 2012 08:17:00 -0700, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > Although making RCU_FANOUT_LEAF a kernel configuration parameter rather
> > than a fixed constant makes it easier for people to decrease cache-miss
> > overhead for large systems, it is of little help for people who must
> > run a single pre-built kernel binary.
> > 
> > This commit therefore allows the value of RCU_FANOUT_LEAF to be
> > increased (but not decreased!) via a boot-time parameter named
> > rcutree.rcu_fanout_leaf.
> ...
> > +static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
> > +module_param(rcu_fanout_leaf, int, 0);
> 
> Maybe it's overkill, but 0400 or 0444 might be a nice touch.

I agree.  0 almost never makes sense; root should almost always have the
ability to read module parameters.  And in this case, I see no reason
not to make it 0444.

- Josh Triplett
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