diff options
Diffstat (limited to 'debian/patches-rt/0073-rcu-Enable-rcu_normal_after_boot-unconditionally-for.patch')
| -rw-r--r-- | debian/patches-rt/0073-rcu-Enable-rcu_normal_after_boot-unconditionally-for.patch | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/debian/patches-rt/0073-rcu-Enable-rcu_normal_after_boot-unconditionally-for.patch b/debian/patches-rt/0073-rcu-Enable-rcu_normal_after_boot-unconditionally-for.patch new file mode 100644 index 000000000..ec9afba35 --- /dev/null +++ b/debian/patches-rt/0073-rcu-Enable-rcu_normal_after_boot-unconditionally-for.patch @@ -0,0 +1,72 @@ +From be1e6f72a91c1c6b65594bba32401b029c7699b8 Mon Sep 17 00:00:00 2001 +From: Julia Cartwright <julia@ni.com> +Date: Tue, 15 Dec 2020 15:16:47 +0100 +Subject: [PATCH 073/323] rcu: Enable rcu_normal_after_boot unconditionally for + RT +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.204-rt100.tar.xz + +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> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + 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 c2afb3304825..23fd09f5351d 100644 +--- a/Documentation/admin-guide/kernel-parameters.txt ++++ b/Documentation/admin-guide/kernel-parameters.txt +@@ -4573,6 +4573,13 @@ + 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 849f0aa99333..dd94a602a6d2 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 +-- +2.43.0 + |