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| author |   Paul E. McKenney <paulmck@linux.ibm.com> | 2019-06-01 06:16:38 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@linux.ibm.com> | 2019-08-13 14:35:49 -0700 |
| commit | 6608c3a027bcc0b34cc02bc764ea9f52b9dce46f (patch) | |
| tree | 6ea50ee8604de4ceee619c830ad2fc1d3c3720a9 /kernel/rcu | |
| parent | rcu/nocb: Round down for number of no-CBs grace-period kthreads (diff) | |
| download | linux-dev-6608c3a027bcc0b34cc02bc764ea9f52b9dce46f.tar.xz linux-dev-6608c3a027bcc0b34cc02bc764ea9f52b9dce46f.zip | |
rcu/nocb: Reduce contention at no-CBs registry-time CB advancement
Currently, __call_rcu_nocb_wake() conditionally acquires the leaf rcu_node
structure's ->lock, and only afterwards does rcu_advance_cbs_nowake()
check to see if it is possible to advance callbacks without potentially
needing to awaken the grace-period kthread. Given that the no-awaken
check can be done locklessly, this commit reverses the order, so that
rcu_advance_cbs_nowake() is invoked without holding the leaf rcu_node
structure's ->lock and rcu_advance_cbs_nowake() checks the grace-period
state before conditionally acquiring that lock, thus reducing the number
of needless acquistions of the leaf rcu_node structure's ->lock.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 5 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 4 |
2 files changed, 4 insertions, 5 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index a6ddfae6978d..ec320658aeef 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1341,10 +1341,11 @@ static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp) static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp, struct rcu_data *rdp) { - raw_lockdep_assert_held_rcu_node(rnp); - if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) + if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || + !raw_spin_trylock_rcu_node(rnp)) return; WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); + raw_spin_unlock_rcu_node(rnp); } /* diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 12212764ecd8..09c15f619e78 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -1668,10 +1668,8 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, if (!rdp->nocb_cb_sleep && rcu_segcblist_ready_cbs(&rdp->cblist)) { // Already going full tilt, so don't try to rewake. - } else if (rcu_segcblist_pend_cbs(&rdp->cblist) && - raw_spin_trylock_rcu_node(rdp->mynode)) { + } else if (rcu_segcblist_pend_cbs(&rdp->cblist)) { rcu_advance_cbs_nowake(rdp->mynode, rdp); - raw_spin_unlock_rcu_node(rdp->mynode); } else { wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE, TPS("WakeOvfIsDeferred")); |