Commit-ID: 8d672fa6bf68ffc36a0c5e4868499f86bbea2308
Gitweb: https://git.kernel.org/tip/8d672fa6bf68ffc36a0c5e4868499f86bbea2308
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 2 May 2018 14:46:43 -0700
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Thu, 12 Jul 2018 15:38:59 -0700
rcu: Make rcu_init_new_rnp() stop upon already-set bit
Currently, rcu_init_new_rnp() walks up the rcu_node combining tree,
setting bits in the ->qsmaskinit fields on the way up. It walks up
unconditionally, regardless of the initial state of these bits. This is
OK because only the corresponding RCU grace-period kthread ever tests
or sets these bits during runtime. However, it is also pointless, and
it increases both memory and lock contention (albeit only slightly), so
this commit stops the walk as soon as an already-set bit is encountered.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
kernel/rcu/tree.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 05f69b787a57..3fe854a15d82 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3479,9 +3479,10 @@ EXPORT_SYMBOL_GPL(rcu_barrier_sched);
static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
{
long mask;
+ long oldmask;
struct rcu_node *rnp = rnp_leaf;
- raw_lockdep_assert_held_rcu_node(rnp);
+ raw_lockdep_assert_held_rcu_node(rnp_leaf);
WARN_ON_ONCE(rnp->wait_blkd_tasks);
for (;;) {
mask = rnp->grpmask;
@@ -3489,8 +3490,11 @@ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
if (rnp == NULL)
return;
raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
+ oldmask = rnp->qsmaskinit;
rnp->qsmaskinit |= mask;
raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
+ if (oldmask)
+ return;
}
}
--
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