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 RFC tip/core/rcu 07/14] rcu/nocb: Reduce nocb_cb_wait() leaf rcu_node ->lock contention
Date: Fri, 2 Aug 2019 08:14:54 -0700 [thread overview]
Message-ID: <20190802151501.13069-7-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190802151435.GA1081@linux.ibm.com>
Currently, nocb_cb_wait() advances callbacks on each pass through its
loop, though only if it succeeds in conditionally acquiring its leaf
rcu_node structure's ->lock. Despite the conditional acquisition of
->lock, this does increase contention. This commit therefore avoids
advancing callbacks unless there are callbacks in ->cblist whose grace
period has completed.
Note that nocb_cb_wait() doesn't worry about callbacks that have not
yet been assigned a grace period. The idea is that the only reason for
nocb_cb_wait() to advance callbacks is to allow it to continue invoking
callbacks. Time will tell whether this is the correct choice.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
kernel/rcu/tree_plugin.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 5db39ce1cae1..02739366ef5d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2076,6 +2076,7 @@ static int rcu_nocb_gp_kthread(void *arg)
*/
static void nocb_cb_wait(struct rcu_data *rdp)
{
+ unsigned long cur_gp_seq;
unsigned long flags;
bool needwake_gp = false;
struct rcu_node *rnp = rdp->mynode;
@@ -2088,7 +2089,9 @@ static void nocb_cb_wait(struct rcu_data *rdp)
local_bh_enable();
lockdep_assert_irqs_enabled();
rcu_nocb_lock_irqsave(rdp, flags);
- if (raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
+ if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
+ rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
+ 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. */
}
--
2.17.1
next prev parent reply other threads:[~2019-08-02 15:15 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-02 15:14 [PATCH tip/core/rcu 0/14] No-CBs bypass addition for v5.4 Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 01/14] rcu/nocb: Atomic ->len field in rcu_segcblist structure Paul E. McKenney
2019-08-04 14:50 ` Peter Zijlstra
2019-08-04 14:52 ` Peter Zijlstra
2019-08-04 18:45 ` Paul E. McKenney
2019-08-04 18:42 ` Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 02/14] rcu/nocb: Add bypass callback queueing Paul E. McKenney
2019-08-07 0:03 ` Joel Fernandes
2019-08-07 0:16 ` Joel Fernandes
2019-08-07 0:35 ` Paul E. McKenney
2019-08-07 0:40 ` Steven Rostedt
2019-08-07 1:17 ` Paul E. McKenney
2019-08-07 1:24 ` Steven Rostedt
2019-08-07 3:47 ` Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 03/14] rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 04/14] rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 05/14] rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake() Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 06/14] rcu/nocb: Advance CBs after merge in rcutree_migrate_callbacks() Paul E. McKenney
2019-08-02 15:14 ` Paul E. McKenney [this message]
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 08/14] rcu/nocb: Reduce __call_rcu_nocb_wake() leaf rcu_node ->lock contention Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 09/14] rcu/nocb: Don't wake no-CBs GP kthread if timer posted under overload Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 10/14] rcu: Allow rcu_do_batch() to dynamically adjust batch sizes Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 11/14] EXP nohz: Add TICK_DEP_BIT_RCU Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 12/14] rcu/nohz: Force on tick when invoking lots of callbacks Paul E. McKenney
2019-08-02 15:15 ` [PATCH RFC tip/core/rcu 13/14] rcutorture: Force on tick for readers and callback flooders Paul E. McKenney
2019-08-02 15:15 ` [PATCH RFC tip/core/rcu 14/14] rcu/nohz: Make multi_cpu_stop() enable tick on all online CPUs Paul E. McKenney
2019-08-04 14:43 ` Peter Zijlstra
2019-08-04 14:48 ` Peter Zijlstra
2019-08-04 18:41 ` Paul E. McKenney
2019-08-04 20:24 ` Paul E. McKenney
2019-08-05 4:19 ` Paul E. McKenney
2019-08-05 8:07 ` Peter Zijlstra
2019-08-05 14:47 ` Paul E. McKenney
2019-08-05 8:05 ` Peter Zijlstra
2019-08-05 14:54 ` Paul E. McKenney
2019-08-05 15:50 ` Peter Zijlstra
2019-08-05 17:48 ` Paul E. McKenney
2019-08-06 18:08 ` Paul E. McKenney
2019-08-07 21:41 ` Paul E. McKenney
2019-08-08 20:35 ` Paul E. McKenney
2019-08-08 21:30 ` Paul E. McKenney
2019-08-09 16:51 ` Paul E. McKenney
2019-08-09 18:07 ` Joel Fernandes
2019-08-09 18:39 ` Paul E. McKenney
2019-08-12 21:02 ` Frederic Weisbecker
2019-08-12 23:23 ` Paul E. McKenney
2019-08-13 1:33 ` Joel Fernandes
2019-08-13 12:30 ` Frederic Weisbecker
2019-08-13 14:48 ` Paul E. McKenney
2019-08-14 17:55 ` Joel Fernandes
2019-08-14 22:05 ` Paul E. McKenney
2019-08-15 15:07 ` Joel Fernandes
2019-08-15 17:23 ` Paul E. McKenney
2019-08-15 18:15 ` Joel Fernandes
2019-08-15 18:39 ` Paul E. McKenney
2019-08-15 19:42 ` Joel Fernandes
2019-08-13 21:06 ` Paul E. McKenney
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