The patch titled
rcu: move PREEMPT_RCU config option back under PREEMPT
has been removed from the -mm tree. Its filename was
rcu-move-preempt_rcu-config-option-back-under-preempt.patch
This patch was dropped because it was merged into mainline or a subsystem tree
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: rcu: move PREEMPT_RCU config option back under PREEMPT
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Acked-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Dipankar Sarma <dipankar@xxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
init/Kconfig | 34 +++-------------------------------
kernel/Kconfig.preempt | 15 +++++++++++++++
2 files changed, 18 insertions(+), 31 deletions(-)
diff -puN init/Kconfig~rcu-move-preempt_rcu-config-option-back-under-preempt init/Kconfig
--- a/init/Kconfig~rcu-move-preempt_rcu-config-option-back-under-preempt
+++ a/init/Kconfig
@@ -865,38 +865,10 @@ 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 -puN kernel/Kconfig.preempt~rcu-move-preempt_rcu-config-option-back-under-preempt kernel/Kconfig.preempt
--- a/kernel/Kconfig.preempt~rcu-move-preempt_rcu-config-option-back-under-preempt
+++ a/kernel/Kconfig.preempt
@@ -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
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are
origin.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
add-rcu_assign_index-if-ever-needed.patch
add-rcu_assign_index-if-ever-needed-fix.patch
rcu-split-listh-and-move-rcu-protected-lists-into-rculisth.patch
isolate-ratelimit-from-printkc-for-other-use.patch
add-warn_on_secs-macro.patch
use-warn_on_secs-in-rcupreempth.patch
lock_task_sighand-add-rcu-lock-unlock.patch
k_getrusage-dont-take-rcu_read_lock.patch
do_task_stat-dont-take-rcu_read_lock.patch
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