From 3e42ec1aa716f10c68294b8492ae3ea684528699 Mon Sep 17 00:00:00 2001
From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Date: Wed, 25 Nov 2015 18:56:00 -0800
Subject: [PATCH] rcu: Allow expedited grace periods to be disabled at init
Expedited grace periods can speed up boot, but are undesirable in
aggressive real-time systems. This commit therefore introduces a
kernel parameter rcupdate.rcu_normal_after_boot that disables
expedited grace periods just before init is spawned.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
Documentation/kernel-parameters.txt | 5 +++++
kernel/rcu/update.c | 5 +++++
2 files changed, 10 insertions(+)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 7673943d30850..197305bbb9b7a 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3318,6 +3318,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
grace-period latency. This parameter overrides
rcupdate.rcu_expedited.
+ rcupdate.rcu_normal_after_boot= [KNL]
+ Once boot has completed (that is, after
+ rcu_end_inkernel_boot() has been invoked), use
+ only normal grace-period primitives.
+
rcupdate.rcu_task_stall_timeout= [KNL]
Set timeout in jiffies for RCU task stall warning
messages. Disable with a value less than or equal
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 8fccda3a794d9..12b91f5a60a62 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -63,6 +63,9 @@ MODULE_ALIAS("rcupdate");
module_param(rcu_expedited, int, 0);
module_param(rcu_normal, int, 0);
+static int rcu_normal_after_boot;
+module_param(rcu_normal_after_boot, int, 0);
+
#if defined(CONFIG_DEBUG_LOCK_ALLOC) && defined(CONFIG_PREEMPT_COUNT)
/**
* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
@@ -178,6 +181,8 @@ void rcu_end_inkernel_boot(void)
{
if (IS_ENABLED(CONFIG_RCU_EXPEDITE_BOOT))
rcu_unexpedite_gp();
+ if (rcu_normal_after_boot)
+ WRITE_ONCE(rcu_normal, 1);
}
#ifdef CONFIG_PREEMPT_RCU
--
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