Currently, nocb_cb_wait() unconditionally acquires the leaf rcu_node ->lock to advance callbacks when done invoking the previous batch. It does this while holding ->nocb_lock, which means that contention on the leaf rcu_node ->lock visits itself on the ->nocb_lock. This commit therefore makes this lock acquisition conditional, forgoing callback advancement when the leaf rcu_node ->lock is not immediately available. (In this case, the no-CBs grace-period kthread will eventually do any needed callback advancement.)
Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/tree_plugin.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index a1a2fc9df6d8..7fbf2c4411a1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1803,9 +1803,10 @@ static void nocb_cb_wait(struct rcu_data *rdp) local_bh_enable(); lockdep_assert_irqs_enabled(); rcu_nocb_lock_irqsave(rdp, flags); - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - needwake_gp = rcu_advance_cbs(rdp->mynode, rdp); - raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ + if (raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */ + needwake_gp = rcu_advance_cbs(rdp->mynode, rdp); + raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ + } if (rcu_segcblist_ready_cbs(&rdp->cblist)) { rcu_nocb_unlock_irqrestore(rdp, flags); if (needwake_gp) -- 2.17.1
