leandrof/linux
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

rcu: Enable rcu_normal_after_boot unconditionally for RT

Browse Source 
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>
This commit is contained in:
Julia Cartwright
2020-12-15 15:16:47 +01:00
committed by Paul E. McKenney
parent 8b9a0ecc7e
commit 36221e109e
2 changed files with 10 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
kernel/rcu/update.c
View File

@@ -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