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

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Date:	Fri, 29 Feb 2008 05:34:54 +0100
From:	Roman Zippel <zippel@...ux-m68k.org>
To:	ego@...ibm.com
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul E McKenney <paulmck@...ibm.com>,
	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 Thursday 13. December 2007, Gautham R Shenoy wrote:

> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index c64ce9c..06cafcc 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -63,3 +63,41 @@ config PREEMPT_BKL
>  	  Say Y here if you are building a kernel for a desktop system.
>  	  Say N if you are unsure.
>
> +choice
> +	prompt "RCU implementation type:"
> +	default CLASSIC_RCU
> +
> +config CLASSIC_RCU
> +	bool "Classic 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.
> +
> +config PREEMPT_RCU
> +	bool "Preemptible RCU"
> +	depends on PREEMPT
> +	help
> +	  This option reduces the latency of the kernel by making certain
> +	  RCU sections preemptible. Normally RCU code is non-preemptible, if
> +	  this option is selected then read-only RCU sections become
> +	  preemptible. This helps latency, but may expose bugs due to
> +	  now-naive assumptions about each RCU read-side critical section
> +	  remaining on a given CPU through its execution.
> +
> +	  Say N if you are unsure.
> +
> +endchoice

Why got this moved into init/Kconfig?
Now it's somewhere in the root menu, not really belonging to anything.
Also why is this a choice? Are more RCU types planned?

bye, Roman
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