diff options
| author | Julia Cartwright <[email protected]> | 2020-12-15 15:16:47 +0100 |
|---|---|---|
| committer | Paul E. McKenney <[email protected]> | 2021-01-04 13:43:51 -0800 |
| commit | 36221e109eb20ac111bc3bf3e8d5639aa457c7e0 (patch) | |
| tree | b636272ab3062d4f1db2e2ab8b11d4ddcef7a8b2 | |
| parent | 8b9a0ecc7ef5e1ed3afbc926de17399a37128c82 (diff) | |
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 <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Signed-off-by: Julia Cartwright <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
[ paulmck: Update kernel-parameters.txt accordingly. ]
Signed-off-by: Paul E. McKenney <[email protected]>
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 7 | ||||
| -rw-r--r-- | kernel/rcu/update.c | 4 |
2 files changed, 10 insertions, 1 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 521255f4ef13..e0008d9caccb 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 39334d2d2b37..b95ae86c40a7 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 |