linux-kernel - Re: [RFC PATCH 4/6] Preempt-RCU: Implementation

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Message-ID: <Pine.LNX.4.64.0802291330590.2723@scrub.home>
Date:	Fri, 29 Feb 2008 13:38:15 +0100 (CET)
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
cc:	ego@...ibm.com, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	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>
Subject: Re: [RFC PATCH 4/6] Preempt-RCU: Implementation

Hi

On Thu, 28 Feb 2008, Paul E. McKenney wrote:

> > Why got this moved into init/Kconfig?
> 
> Because there are some arches that don't have kernel/Kconfig.preempt,
> its earlier home.  Therefore, putting it into kernel/Kconfig.preempt
> broke those arches' builds by supplying neither PREEMPT_RCU nor
> CLASSIC_RCU.
> 
> > Now it's somewhere in the root menu, not really belonging to anything.
> 
> Do you have a suggested location?
> 
> > Also why is this a choice? Are more RCU types planned?
> 
> I don't expect additional drop-in replacements for RCU, though people
> are certainly free to experiment if they wish.  It is a choice because
> this gives people a very clear idea of the two options and because
> it makes the implementation a bit cleaner.

I'd suggest to move PREEMPT_RCU back to Kconfig.preempt and if you really 
need the second symbol leave this behind (maybe with a comment):

config CLASSIC_RCU
	def_bool !PREEMPT_RCU

Once there are more options, we can still look for a better place...

Also could you please add a proper dependency to RCU_TRACE on PREEMPT_RCU, 
so that this condition isn't needed anymore:

ifeq ($(CONFIG_PREEMPT_RCU),y)
obj-$(CONFIG_RCU_TRACE) += rcupreempt_trace.o
endif

Thanks.

bye, Roman
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