On Fri, Feb 29, 2008 at 05:34:54AM +0100, Roman Zippel wrote:

Hi,

On Thursday 13. December 2007, Gautham R Shenoy wrote:

quoted

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?

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.

							Thanx, Paul