linux-kernel - Re: preemptible RCU bug (was Re: [git pull] scheduler changes for v2.6.25)

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Date:	Sun, 27 Jan 2008 03:05:59 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: preemptible RCU bug (was Re: [git pull] scheduler changes for v2.6.25)

On Sat, Jan 26, 2008 at 08:19:21PM +0100, Stefan Richter wrote:
> Ingo Molnar wrote:
> >  - Paul E. McKenney's preemptible RCU code.
> 
> BUG:  New Kconfig option without help text.
> 
> $ make oldconfig
> RCU implementation type:
> > 1. Classic RCU (CLASSIC_RCU) (NEW)
>   2. Preemptible RCU (PREEMPT_RCU) (NEW)
> choice[1-2]: ?
> 
> Sorry, no help available for this option yet.

Good catch!!!

This patch supplies help text for the "RCU implementation type"
kernel configuration choice.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---

 Kconfig.preempt |    8 ++++++++
 1 file changed, 8 insertions(+)

diff -urpNa -X dontdiff linux-2.6.24-rt1/kernel/Kconfig.preempt linux-2.6.24-rt1-RCUconfighelp/kernel/Kconfig.preempt
--- linux-2.6.24-rt1/kernel/Kconfig.preempt	2008-01-27 02:52:36.000000000 -0800
+++ linux-2.6.24-rt1-RCUconfighelp/kernel/Kconfig.preempt	2008-01-27 03:05:22.000000000 -0800
@@ -131,6 +131,14 @@ choice
 	prompt "RCU implementation type:"
 	default PREEMPT_RCU if PREEMPT_RT
 	default CLASSIC_RCU
+	help
+	  This allows you to choose either the classic RCU implementation
+	  that is designed for best read-side performance on non-realtime
+	  systems, or the preemptible RCU implementation for best latency
+	  on realtime systems.  Note that some kernel preemption modes
+	  will restrict your choice.
+
+	  Select the default if you are unsure.
 
 config CLASSIC_RCU
 	bool "Classic RCU"
--
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