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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 02/10] rcu/nocb: Never downgrade ->nocb_defer_wakeup in wake_nocb_gp_defer()
Date: Thu,  1 Aug 2019 16:16:27 -0700	[thread overview]
Message-ID: <20190801231636.23115-2-paulmck@linux.ibm.com> (raw)
In-Reply-To: <20190801231619.GA22610@linux.ibm.com>

Currently, wake_nocb_gp_defer() simply stores whatever waketype was
passed in, which can result in a RCU_NOCB_WAKE_FORCE being downgraded
to RCU_NOCB_WAKE, which could in turn delay callback processing.
This commit therefore adds a check so that wake_nocb_gp_defer() only
updates ->nocb_defer_wakeup when the update increases the forcefulness,
thus avoiding downgrades.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
---
 kernel/rcu/tree_plugin.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 297b38732e28..f93603ca1672 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1598,7 +1598,8 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
 {
 	if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
 		mod_timer(&rdp->nocb_timer, jiffies + 1);
-	WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
+	if (rdp->nocb_defer_wakeup < waketype)
+		WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
 	trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
 }
 
-- 
2.17.1


  parent reply	other threads:[~2019-08-01 23:17 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 ` Paul E. McKenney [this message]
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 ` [PATCH tip/core/rcu 08/10] rcu/nocb: Reduce contention at no-CBs invocation-done time Paul E. McKenney
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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