[PATCH 12/19] rcu/nocb: Process batch locally as long as offloading isn't complete

From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E . McKenney" <paulmck@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	Josh Triplett <josh@joshtriplett.org>,
	rcu@vger.kernel.org
Subject: [PATCH 12/19] rcu/nocb: Process batch locally as long as offloading isn't complete
Date: Fri, 13 Nov 2020 13:13:27 +0100	[thread overview]
Message-ID: <20201113121334.166723-13-frederic@kernel.org> (raw)
In-Reply-To: <20201113121334.166723-1-frederic@kernel.org>

During the offloading or de-offloading process, make sure to process
the callbacks batch locally whenever the segcblist isn't entirely
offloaded. This enforces callback service processing while we are still
in intermediate (de-)offloading state.

CHECKME: Note that __call_rcu_core() isn't called during these intermediate
states. Some pieces there may still be necessary.

Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
---
 kernel/rcu/rcu_segcblist.h | 12 ++++++++++++
 kernel/rcu/tree.c          |  3 ++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h
index f42f7a13faa0..c8f4d4ac650f 100644
--- a/kernel/rcu/rcu_segcblist.h
+++ b/kernel/rcu/rcu_segcblist.h
@@ -92,6 +92,18 @@ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp)
 	return false;
 }
 
+static inline bool rcu_segcblist_completely_offloaded(struct rcu_segcblist *rsclp)
+{
+	int flags = SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP | SEGCBLIST_OFFLOADED;
+
+	if (IS_ENABLED(CONFIG_RCU_NOCB_CPU)) {
+		if ((rsclp->flags & flags) == flags)
+			return true;
+	}
+
+	return false;
+}
+
 /*
  * Are all segments following the specified segment of the specified
  * rcu_segcblist structure empty of callbacks?  (The specified
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index da1ecf60c541..cc141337f3f9 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2691,6 +2691,7 @@ static __latent_entropy void rcu_core(void)
 	struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
 	struct rcu_node *rnp = rdp->mynode;
 	const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist);
+	const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
 
 	if (cpu_is_offline(smp_processor_id()))
 		return;
@@ -2720,7 +2721,7 @@ static __latent_entropy void rcu_core(void)
 	rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
 
 	/* If there are callbacks ready, invoke them. */
-	if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) &&
+	if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
 	    likely(READ_ONCE(rcu_scheduler_fully_active)))
 		rcu_do_batch(rdp);
 
-- 
2.25.1

