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rcu: Move grace-period pre-init delay after pre-init

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The main race with the early part of grace-period initialization appears
to be with CPU hotplug.  To more fully open this race window, this commit
moves the rcu_gp_slow() from the beginning of the early initialization
loop to follow that loop, thus widening the race window, especially for
the rcu_node structures that are initialized last.  This commit also
expands rcutree.gp_preinit_delay from 3 to 12, giving the same overall
delay in the grace period, but concentrated in the spot where it will
do the most good.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-05-03 13:40:25 -07:00
parent 1f3e5f51b9
commit f34f2f5852
2 changed files with 2 additions and 2 deletions
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2
kernel/rcu/tree.c
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@ -1900,7 +1900,6 @@ static bool rcu_gp_init(struct rcu_state *rsp)
* will handle subsequent offline CPUs. * will handle subsequent offline CPUs.
*/ */
rcu_for_each_leaf_node(rsp, rnp) { rcu_for_each_leaf_node(rsp, rnp) {
rcu_gp_slow(rsp, gp_preinit_delay);
spin_lock(&rsp->ofl_lock); spin_lock(&rsp->ofl_lock);
raw_spin_lock_irq_rcu_node(rnp); raw_spin_lock_irq_rcu_node(rnp);
if (rnp->qsmaskinit == rnp->qsmaskinitnext && if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
@ -1945,6 +1944,7 @@ static bool rcu_gp_init(struct rcu_state *rsp)
raw_spin_unlock_irq_rcu_node(rnp); raw_spin_unlock_irq_rcu_node(rnp);
spin_unlock(&rsp->ofl_lock); spin_unlock(&rsp->ofl_lock);
} }
rcu_gp_slow(rsp, gp_preinit_delay); /* Races with CPU hotplug. */
/* /*
* Set the quiescent-state-needed bits in all the rcu_node * Set the quiescent-state-needed bits in all the rcu_node

2
tools/testing/selftests/rcutorture/configs/rcu/TREE03.boot
View File

@ -1,5 +1,5 @@
rcutorture.onoff_interval=1 rcutorture.onoff_holdoff=30 rcutorture.onoff_interval=1 rcutorture.onoff_holdoff=30
rcutree.gp_preinit_delay=3 rcutree.gp_preinit_delay=12
rcutree.gp_init_delay=3 rcutree.gp_init_delay=3
rcutree.gp_cleanup_delay=3 rcutree.gp_cleanup_delay=3
rcutree.kthread_prio=2 rcutree.kthread_prio=2