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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>
This commit is contained in:
Paul E. McKenney 2015-11-25 18:56:00 -08:00
parent 967dcb8fe6
commit 3e42ec1aa7
2 changed files with 10 additions and 0 deletions
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5
Documentation/kernel-parameters.txt
View File

@ -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

5
kernel/rcu/update.c
View File

@ -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