linux-kernel - Re: [PATCH] move PREEMPT_RCU config option back under PREEMPT

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Message-ID: <20080305005816.GG9517@linux.vnet.ibm.com>
Date:	Tue, 4 Mar 2008 16:58:16 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	ego@...ibm.com, Ingo Molnar <mingo@...e.hu>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ted Tso <tytso@...ibm.com>, dvhltc@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>, bunk@...nel.org,
	Josh Triplett <josh@...edesktop.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>, zippel@...ux-m68k.org
Subject: Re: [PATCH] move PREEMPT_RCU config option back under PREEMPT

On Tue, Mar 04, 2008 at 03:55:42PM -0500, Steven Rostedt wrote:
> 
> On Tue, 4 Mar 2008, Paul E. McKenney wrote:
> >
> > The original preemptible-RCU patch put the choice between classic and
> > preemptible RCU into kernel/Kconfig.preempt, which resulted in build
> > failures on machines not supporting CONFIG_PREEMPT.  This choice was
> > therefore moved to init/Kconfig, which worked, but placed the choice
> > between classic and preemptible RCU at the top level, a very obtuse choice
> > indeed.  This patch changes from the Kconfig "choice" mechanism to a pair
> > of booleans, only one of which (CONFIG_PREEMPT_RCU) is user-visible,
> > and is located in kernel/Kconfig.preempt, where one would expect it
> > to be.  The other (CONFIG_CLASSIC_RCU) is in init/Kconfig so that it
> > is available to all architectures, hopefully avoiding build breakage.
> > Thanks to Roman Zippel for suggesting this approach.
> >
> > I have tested this, but sadly do not have access to a machine that does
> > not support CONFIG_PREEMPT.  However, I did edit my config in an attempt
> > to simulate this situation.
> 
> One minor comment, but otherwise:
> 
> Acked-by: Steven Rostedt <srostedt@...hat.com>
> 
> >
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> 
> 
> >  config CLASSIC_RCU
> > -	bool "Classic RCU"
> > +	def_bool !PREEMPT_RCU
> >  	help
> >  	  This option selects the classic RCU implementation that is
> >  	  designed for best read-side performance on non-realtime
> > -	  systems.
> > -
> > -	  Say Y if you are unsure.
> > -
> 
> You can get rid of the "help" part since it isn't visible to users.

So how about if I replace it with comment lines (starting with "#",
not with "comment")?

						Thanx, Paul
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