lkml.org 
[lkml]   [2008]   [Mar]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] move PREEMPT_RCU config option back under PREEMPT
Hello!

The original preemptible-RCU patch put the choice between classic and
preemptible RCU into kernel/Kconfig.preempt, which resulted in build
failures on machines not supporting CONFIG_PREEMPT. This choice was
therefore moved to init/Kconfig, which worked, but placed the choice
between classic and preemptible RCU at the top level, a very obtuse choice
indeed. This patch changes from the Kconfig "choice" mechanism to a pair
of booleans, only one of which (CONFIG_PREEMPT_RCU) is user-visible,
and is located in kernel/Kconfig.preempt, where one would expect it
to be. The other (CONFIG_CLASSIC_RCU) is in init/Kconfig so that it
is available to all architectures, hopefully avoiding build breakage.
Thanks to Roman Zippel for suggesting this approach.

I have tested this, but sadly do not have access to a machine that does
not support CONFIG_PREEMPT. However, I did edit my config in an attempt
to simulate this situation.

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

init/Kconfig | 34 +++-------------------------------
kernel/Kconfig.preempt | 15 +++++++++++++++
2 files changed, 18 insertions(+), 31 deletions(-)

diff -urpNa -X dontdiff linux-2.6.25-rc3/init/Kconfig linux-2.6.25-rc3-preempt_rcu/init/Kconfig
--- linux-2.6.25-rc3/init/Kconfig 2008-02-26 16:58:42.000000000 -0800
+++ linux-2.6.25-rc3-preempt_rcu/init/Kconfig 2008-03-01 11:30:59.000000000 -0800
@@ -860,38 +860,10 @@ source "block/Kconfig"
config PREEMPT_NOTIFIERS
bool

-choice
- prompt "RCU implementation type:"
- 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"
+ def_bool !PREEMPT_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
+ systems. Classic RCU is the default. Note that the
+ PREEMPT_RCU symbol is used to select/deselect this option.
diff -urpNa -X dontdiff linux-2.6.25-rc3/kernel/Kconfig.preempt linux-2.6.25-rc3-preempt_rcu/kernel/Kconfig.preempt
--- linux-2.6.25-rc3/kernel/Kconfig.preempt 2008-02-26 16:58:42.000000000 -0800
+++ linux-2.6.25-rc3-preempt_rcu/kernel/Kconfig.preempt 2008-03-01 11:35:39.000000000 -0800
@@ -52,8 +52,23 @@ config PREEMPT

endchoice

+config PREEMPT_RCU
+ bool "Preemptible RCU"
+ depends on PREEMPT
+ default n
+ 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.
+
config RCU_TRACE
bool "Enable tracing for RCU - currently stats in debugfs"
+ depends on PREEMPT_RCU
select DEBUG_FS
default y
help

\
 
 \ /
  Last update: 2008-03-04 21:35    [W:0.088 / U:0.460 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site