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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
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.17-rt8.tar.xz
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>
---
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
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