From: Julia Cartwright <julia@ni.com>
Date: Wed, 12 Oct 2016 11:21:14 -0500
Subject: [PATCH] rcu: enable rcu_normal_after_boot by default for RT
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: da77ceac3d20f27310a07a7c346a4ee6b40d6c28
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

The forcing of an expedited grace period is an expensive and very
RT-application unfriendly operation, as it forcibly preempts all running
tasks on CPUs which are preventing the gp from expiring.

By default, as a policy decision, disable the expediting of grace
periods (after boot) on configurations which enable PREEMPT_RT.

Suggested-by: Luiz Capitulino <lcapitulino@redhat.com>
Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
 kernel/rcu/update.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -55,8 +55,10 @@ extern int rcu_expedited; /* from sysctl
 module_param(rcu_expedited, int, 0);
 extern int rcu_normal; /* from sysctl */
 module_param(rcu_normal, int, 0);
-static int rcu_normal_after_boot;
+static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT);
+#ifndef CONFIG_PREEMPT_RT
 module_param(rcu_normal_after_boot, int, 0);
+#endif
 #endif /* #ifndef CONFIG_TINY_RCU */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC