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[PATCH tip/core/rcu 01/20] rcu: update: Make RCU_EXPEDITE_BOOT be the default

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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

RCU_EXPEDITE_BOOT should speed up the boot process by enforcing
synchronize_rcu_expedited() instead of synchronize_rcu() during the boot
process. There should be no reason why one does not want this and there
is no need worry about real time latency at this point.
Therefore make it default.

Note that users wishing to avoid expediting entirely, for example when
bringing up new hardware possibly having flaky IPIs, can use the
rcu_normal boot parameter to override boot-time expediting.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ paulmck: Reworded commit log. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 init/Kconfig        | 13 -------------
 kernel/rcu/update.c |  6 ++----
 2 files changed, 2 insertions(+), 17 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 223b734abccd..96e6d56acd50 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -781,19 +781,6 @@ config RCU_NOCB_CPU_ALL
 
 endchoice
 
-config RCU_EXPEDITE_BOOT
-	bool
-	default n
-	help
-	  This option enables expedited grace periods at boot time,
-	  as if rcu_expedite_gp() had been invoked early in boot.
-	  The corresponding rcu_unexpedite_gp() is invoked from
-	  rcu_end_inkernel_boot(), which is intended to be invoked
-	  at the end of the kernel-only boot sequence, just before
-	  init is exec'ed.
-
-	  Accept the default if unsure.
-
 endmenu # "RCU Subsystem"
 
 config BUILD_BIN2C
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 4f6db7e6a117..9e03db9ea9c0 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -132,8 +132,7 @@ bool rcu_gp_is_normal(void)
 }
 EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
 
-static atomic_t rcu_expedited_nesting =
-	ATOMIC_INIT(IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT) ? 1 : 0);
+static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
 
 /*
  * Should normal grace-period primitives be expedited?  Intended for
@@ -182,8 +181,7 @@ EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
  */
 void rcu_end_inkernel_boot(void)
 {
-	if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
-		rcu_unexpedite_gp();
+	rcu_unexpedite_gp();
 	if (rcu_normal_after_boot)
 		WRITE_ONCE(rcu_normal, 1);
 }
-- 
2.5.2

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[PATCH tip/core/rcu 0/20] Miscellaneous fixes for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 19/20] rcu: Eliminate unused expedited_normal counter "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 12/20] rcu: Re-enable TASKS_RCU for User Mode Linux "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 20/20] rcu: Add lockdep checks to synchronous expedited primitives "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 16/20] rcu: Enable RCU tracepoints by default to aid in debugging "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 03/20] Fix: Disable sys_membarrier when nohz_full is enabled "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 17/20] rcu: Fix comment in rcu_organize_nocb_kthreads() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 10/20] rcu: Add functions to test for trivial grace periods "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
    Re: [PATCH tip/core/rcu 10/20] rcu: Add functions to test for  trivial grace periods Josh Triplett <josh@joshtriplett.org> - 2017-01-16 09:10 +0100
  [PATCH tip/core/rcu 04/20] rcu: Only dump stalled-tasks stacks if there was a real stall "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 18/20] llist: Clarify comments about when locking is needed "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 15/20] rcu: Make rcu_cpu_starting() use its "cpu" argument "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 05/20] rcu: Remove unneeded rcu_process_callbacks() declarations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  [PATCH tip/core/rcu 01/20] rcu: update: Make RCU_EXPEDITE_BOOT be the default "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-14 10:20 +0100
  Re: [PATCH tip/core/rcu 0/20] Miscellaneous fixes for 4.11 Josh Triplett <josh@joshtriplett.org> - 2017-01-16 09:20 +0100

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