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From: paulmck@kernel.org
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
	mingo@kernel.org, jiangshanlai@gmail.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,
	Frederic Weisbecker <frederic@kernel.org>,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH tip/core/rcu 13/21] rcu/nocb: Locally accelerate callbacks as long as offloading isn't complete
Date: Tue,  5 Jan 2021 20:48:45 -0800
Message-ID: <20210106044853.20812-13-paulmck@kernel.org> (raw)
In-Reply-To: <20210106013950.GA14663@paulmck-ThinkPad-P72>

From: Frederic Weisbecker <frederic@kernel.org>

The local callbacks processing checks if any callbacks need acceleration.
This commit carries out this checking under nocb lock protection in
the middle of toggle operations, during which time rcu_core() executes
concurrently with GP/CB kthreads.

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>
Inspired-by: Paul E. McKenney <paulmck@kernel.org>
Tested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 kernel/rcu/tree.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ec14c01..03810a5 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2699,7 +2699,6 @@ static __latent_entropy void rcu_core(void)
 	unsigned long flags;
 	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()))
@@ -2720,11 +2719,11 @@ static __latent_entropy void rcu_core(void)
 
 	/* No grace period and unregistered callbacks? */
 	if (!rcu_gp_in_progress() &&
-	    rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
-		local_irq_save(flags);
+	    rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
+		rcu_nocb_lock_irqsave(rdp, flags);
 		if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
 			rcu_accelerate_cbs_unlocked(rnp, rdp);
-		local_irq_restore(flags);
+		rcu_nocb_unlock_irqrestore(rdp, flags);
 	}
 
 	rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
-- 
2.9.5


  parent reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-06  1:39 [PATCH tip/core/rcu 0/21] Provide runtime switching of offloaded CPUs Paul E. McKenney
2021-01-06  4:48 ` [PATCH tip/core/rcu 01/21] rcu/nocb: Turn enabled/offload states into a common flag paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 02/21] rcu/nocb: Provide basic callback offloading state machine bits paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 03/21] rcu/nocb: Always init segcblist on CPU up paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 04/21] rcu/nocb: De-offloading CB kthread paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 05/21] rcu/nocb: Don't deoffload an offline CPU with pending work paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 06/21] rcu/nocb: De-offloading GP kthread paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 07/21] rcu/nocb: Re-offload support paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 08/21] rcu/nocb: Shutdown nocb timer on de-offloading paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 09/21] rcu/nocb: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 10/21] rcu/nocb: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 11/21] rcu/nocb: Only cond_resched() from actual offloaded batch processing paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 12/21] rcu/nocb: Process batch locally as long as offloading isn't complete paulmck
2021-01-06  4:48 ` paulmck [this message]
2021-01-06  4:48 ` [PATCH tip/core/rcu 14/21] cpu/hotplug: Add lockdep_is_cpus_held() paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 15/21] timer: Add timer_curr_running() paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 16/21] rcutorture: Test runtime toggling of CPUs' callback offloading paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 17/21] tools/rcutorture: Support nocb toggle in TREE01 paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 18/21] rcu/nocb: Add grace period and task state to show_rcu_nocb_state() output paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 19/21] rcu/nocb: Add nocb CB kthread list " paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 20/21] rcu/nocb: Code-style nits in callback-offloading toggling paulmck
2021-01-06  4:48 ` [PATCH tip/core/rcu 21/21] rcu: Do any deferred nocb wakeups at CPU offline time paulmck

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