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

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Message-ID: <Pine.LNX.4.58.0803041553240.11062@gandalf.stny.rr.com>
Date:	Tue, 4 Mar 2008 15:55:42 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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, 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.

-- Steve

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