From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org,
jiangshanlai@gmail.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@linux.ibm.com>
Subject: [PATCH tip/core/rcu 08/10] rcu/nocb: Reduce contention at no-CBs invocation-done time
Date: Thu, 1 Aug 2019 16:16:33 -0700 [thread overview]
Message-ID: <20190801231636.23115-8-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190801231619.GA22610@linux.ibm.com>
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 <paulmck@linux.ibm.com>
---
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
next prev parent reply other threads:[~2019-08-01 23:16 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 23:16 [PATCH tip/core/rcu 0/10] No-CBs contention-reduction updates for v5.3-rc2 Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 01/10] rcu/nocb: Enable re-awakening under high callback load Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 02/10] rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer() Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 03/10] rcu/nocb: Make __call_rcu_nocb_wake() safe for many callbacks Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 04/10] rcu/nocb: Avoid needless wakeups of no-CBs grace-period kthread Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 05/10] rcu/nocb: Avoid ->nocb_lock capture by corresponding CPU Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 06/10] rcu/nocb: Round down for number of no-CBs grace-period kthreads Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 07/10] rcu/nocb: Reduce contention at no-CBs registry-time CB advancement Paul E. McKenney
2019-08-01 23:16 ` Paul E. McKenney [this message]
2019-08-01 23:16 ` [PATCH tip/core/rcu 09/10] rcu/nocb: Reduce ->nocb_lock contention with separate ->nocb_gp_lock Paul E. McKenney
2019-08-01 23:16 ` [PATCH tip/core/rcu 10/10] rcu/nocb: Unconditionally advance and wake for excessive CBs Paul E. McKenney
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