From: "tip-bot2 for Julia Cartwright" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Luiz Capitulino <lcapitulino@redhat.com>,
"Paul E. McKenney" <paulmck@linux.ibm.com>,
Julia Cartwright <julia@ni.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
"Paul E. McKenney" <paulmck@kernel.org>,
x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [tip: core/rcu] rcu: Enable rcu_normal_after_boot unconditionally for RT
Date: Mon, 15 Feb 2021 14:55:45 -0000 [thread overview]
Message-ID: <161340094568.20312.13010770270932827765.tip-bot2@tip-bot2> (raw)
The following commit has been merged into the core/rcu branch of tip:
Commit-ID: 36221e109eb20ac111bc3bf3e8d5639aa457c7e0
Gitweb: https://git.kernel.org/tip/36221e109eb20ac111bc3bf3e8d5639aa457c7e0
Author: Julia Cartwright <julia@ni.com>
AuthorDate: Tue, 15 Dec 2020 15:16:47 +01:00
Committer: Paul E. McKenney <paulmck@kernel.org>
CommitterDate: Mon, 04 Jan 2021 13:43:51 -08:00
rcu: Enable rcu_normal_after_boot unconditionally for RT
Expedited RCU grace periods send IPIs to all non-idle CPUs, and thus can
disrupt time-critical code in real-time applications. However, there
is a portion of boot-time processing (presumably before any real-time
applications have started) where expedited RCU grace periods are the only
option. And so it is that experience with the -rt patchset indicates that
PREEMPT_RT systems should always set the rcupdate.rcu_normal_after_boot
kernel boot parameter.
This commit therefore makes the post-boot application environment safe
for real-time applications by making PREEMPT_RT systems disable the
rcupdate.rcu_normal_after_boot kernel boot parameter and acting as
if this parameter had been set. This means that post-boot calls to
synchronize_rcu_expedited() will be treated as if they were instead
calls to synchronize_rcu(), thus preventing the IPIs, and thus avoiding
disrupting real-time applications.
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>
[ paulmck: Update kernel-parameters.txt accordingly. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
Documentation/admin-guide/kernel-parameters.txt | 7 +++++++
kernel/rcu/update.c | 4 +++-
2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 521255f..e0008d9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4474,6 +4474,13 @@
only normal grace-period primitives. No effect
on CONFIG_TINY_RCU kernels.
+ But note that CONFIG_PREEMPT_RT=y kernels enables
+ this kernel boot parameter, forcibly setting
+ it to the value one, that is, converting any
+ post-boot attempt at an expedited RCU grace
+ period to instead use normal non-expedited
+ grace-period processing.
+
rcupdate.rcu_task_ipi_delay= [KNL]
Set time in jiffies during which RCU tasks will
avoid sending IPIs, starting with the beginning
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 39334d2..b95ae86 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -56,8 +56,10 @@
#ifndef CONFIG_TINY_RCU
module_param(rcu_expedited, int, 0);
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
reply other threads:[~2021-02-15 15:06 UTC|newest]
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