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Commit 3e42ec1a authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

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: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 967dcb8f

Documentation/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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

kernel/rcu/update.c

+5 −0
Original line number Diff line number Diff line
@@ -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