From: Frederic Weisbecker <frederic@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
"Paul E . McKenney" <paulmck@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Neeraj Upadhyay <neeraju@codeaurora.org>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>
Subject: [PATCH 06/16] rcu/nocb: Don't deoffload an offline CPU with pending work
Date: Fri, 23 Oct 2020 16:46:39 +0200 [thread overview]
Message-ID: <20201023144649.53046-7-frederic@kernel.org> (raw)
In-Reply-To: <20201023144649.53046-1-frederic@kernel.org>
Offlining offloaded CPUs don't migrate their callbacks just like
non-offloaded CPUs do. It's up to their CB/GP kthread to handle what
remains.
Therefore we can't afford to de-offload an offline CPU that still has
pending work to do, or the callbacks would be ignored.
NOTE: The long term solution will be to wait for all pending callbacks
to be processed before completing a CPU down operation.
Suggested-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>
---
kernel/rcu/tree_plugin.h | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 09caf319a4a9..33e9d53d2181 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2228,6 +2228,14 @@ static int __rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
printk("De-offloading %d\n", rdp->cpu);
rcu_nocb_lock_irqsave(rdp, flags);
+ /*
+ * If there are still pending work offloaded, the offline
+ * CPU won't help much handling them.
+ */
+ if (cpu_is_offline(rdp->cpu) && !rcu_segcblist_empty(&rdp->cblist)) {
+ rcu_nocb_unlock_irqrestore(rdp, flags);
+ return -EBUSY;
+ }
raw_spin_lock_rcu_node(rnp);
rcu_segcblist_offload(cblist, false);
raw_spin_unlock_rcu_node(rnp);
--
2.25.1
next prev parent reply other threads:[~2020-10-23 14:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-23 14:46 [PATCH 00/16] rcu/nocb: De-offload and re-offload support v3 Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 01/16] rcu: Implement rcu_segcblist_is_offloaded() config dependent Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 02/16] rcu: Turn enabled/offload states into a common flag Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 03/16] rcu: Provide basic callback offloading state machine bits Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 04/16] rcu/nocb: Always init segcblist on CPU up Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 05/16] rcu: De-offloading CB kthread Frederic Weisbecker
2020-11-02 13:38 ` Boqun Feng
2020-11-04 14:31 ` Frederic Weisbecker
2020-11-04 14:42 ` Boqun Feng
2020-11-04 14:45 ` Frederic Weisbecker
2020-10-23 14:46 ` Frederic Weisbecker [this message]
2020-10-23 14:46 ` [PATCH 07/16] rcu: De-offloading GP kthread Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 08/16] rcu: Re-offload support Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 09/16] rcu: Shutdown nocb timer on de-offloading Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 10/16] rcu: Flush bypass before setting SEGCBLIST_SOFTIRQ_ONLY Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 11/16] rcu: Set SEGCBLIST_SOFTIRQ_ONLY at the very last stage of de-offloading Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 12/16] rcu/nocb: Only cond_resched() from actual offloaded batch processing Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 13/16] rcu: Process batch locally as long as offloading isn't complete Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 14/16] rcu: Locally accelerate callbacks " Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 15/16] rcutorture: Test runtime toggling of CPUs' callback offloading Frederic Weisbecker
2020-10-23 14:46 ` [PATCH 16/16] tools/rcutorture: Support nocb toggle in TREE01 Frederic Weisbecker
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