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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2008-03-10 14:43:57 -0400
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-03-10 21:01:20 -0400
commit21bbb39c376ce6beeeb549d155f0d53dc76ed000 (patch)
tree762d0ae6d1cd88aaa231739c3e88437e52ffa387 /init
parentf47831fabaf0206abc56ee5a33fd006fe29b6dc6 (diff)
rcu: move PREEMPT_RCU config option back under PREEMPT
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. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: Dipankar Sarma <dipankar@in.ibm.com> Cc: Josh Triplett <josh@freedesktop.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'init')
-rw-r--r--init/Kconfig34
1 files changed, 3 insertions, 31 deletions
diff --git a/init/Kconfig b/init/Kconfig
index 074ac97f55e3..a97924bc5b8d 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -865,38 +865,10 @@ source "block/Kconfig"
865config PREEMPT_NOTIFIERS 865config PREEMPT_NOTIFIERS
866 bool 866 bool
867 867
868choice
869 prompt "RCU implementation type:"
870 default CLASSIC_RCU
871 help
872 This allows you to choose either the classic RCU implementation
873 that is designed for best read-side performance on non-realtime
874 systems, or the preemptible RCU implementation for best latency
875 on realtime systems. Note that some kernel preemption modes
876 will restrict your choice.
877
878 Select the default if you are unsure.
879
880config CLASSIC_RCU 868config CLASSIC_RCU
881 bool "Classic RCU" 869 def_bool !PREEMPT_RCU
882 help 870 help
883 This option selects the classic RCU implementation that is 871 This option selects the classic RCU implementation that is
884 designed for best read-side performance on non-realtime 872 designed for best read-side performance on non-realtime
885 systems. 873 systems. Classic RCU is the default. Note that the
886 874 PREEMPT_RCU symbol is used to select/deselect this option.
887 Say Y if you are unsure.
888
889config PREEMPT_RCU
890 bool "Preemptible RCU"
891 depends on PREEMPT
892 help
893 This option reduces the latency of the kernel by making certain
894 RCU sections preemptible. Normally RCU code is non-preemptible, if
895 this option is selected then read-only RCU sections become
896 preemptible. This helps latency, but may expose bugs due to
897 now-naive assumptions about each RCU read-side critical section
898 remaining on a given CPU through its execution.
899
900 Say N if you are unsure.
901
902endchoice