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

From: Paul E. McKenney
Date: Sun Jan 27 2008 - 06:06:22 EST


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@xxxxxxxxxxxxxxxxxx>
---

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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