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

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Message-ID: <20120701174553.GB15481@leaf>
Date:	Sun, 1 Jul 2012 10:45:53 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	Rusty Russell <rusty@...abs.org>, 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 05:52:22AM -0700, Paul E. McKenney wrote:
> On Sun, Jul 01, 2012 at 12:17:58AM -0700, Josh Triplett wrote:
> > 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.
> 
> Should I do the same for these parameters as well?
> 
> kernel/rcutree.c:module_param(blimit, int, 0);
> kernel/rcutree.c:module_param(qhimark, int, 0);
> kernel/rcutree.c:module_param(qlowmark, int, 0);

Yes, all of those should become 0444.

- Josh Triplett
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