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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Frederic Weisbecker <frederic@kernel.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Uladzislau Rezki <urezki@gmail.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Boqun Feng <boqun.feng@gmail.com>,
	Neeraj Upadhyay <neeraju@codeaurora.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Joel Fernandes <joel@joelfernandes.org>,
	rcu@vger.kernel.org
Subject: Re: [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread
Date: Thu, 30 Sep 2021 17:37:37 +0200	[thread overview]
Message-ID: <20210930153737.lljjay2cquph7cfv@linutronix.de> (raw)
In-Reply-To: <20210929221012.228270-12-frederic@kernel.org>

On 2021-09-30 00:10:12 [+0200], Frederic Weisbecker wrote:
> rcu_core() tries to ensure that its self-invocation in case of callbacks
> overload only happen in softirq/rcuc mode. Indeed it doesn't make sense
> to trigger local RCU core from nocb_cb kthread since it can execute
> on a CPU different from the target rdp. Also in case of overload, the
> nocb_cb kthread simply iterates a new loop of callbacks processing.
> 
> However the "offloaded" check that aims at preventing that is wrong.
- that?

> First of all that state is volatile and second: softirq/rcuc can
> execute while the target rdp is offloaded. As a result rcu_core() can

can what?

> Fix that with moving the rcu_core() self-invocation to rcu_core() itself,
> irrespective of the rdp offloaded state.

Sebastian

  reply	other threads:[~2021-09-30 15:37 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-29 22:10 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 01/11] rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 02/11] rcu/nocb: Prepare state machine for a new step Frederic Weisbecker
2021-10-01 17:48   ` Valentin Schneider
2021-10-04 11:35     ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 03/11] rcu/nocb: Invoke rcu_core() at the start of deoffloading Frederic Weisbecker
2021-10-01 17:50   ` Valentin Schneider
2021-10-04 12:41     ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 04/11] rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe Frederic Weisbecker
2021-10-01 17:50   ` Valentin Schneider
2021-09-29 22:10 ` [PATCH 05/11] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe Frederic Weisbecker
2021-10-01 17:50   ` Valentin Schneider
2021-10-04 13:14     ` Frederic Weisbecker
2021-09-29 22:10 ` [RFC PATCH 06/11] rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 07/11] rcu/nocb: Use appropriate rcu_nocb_lock_irqsave() Frederic Weisbecker
2021-10-01 17:50   ` Valentin Schneider
2021-10-04 13:33     ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 08/11] rcu/nocb: Limit number of softirq callbacks only on softirq Frederic Weisbecker
2021-10-01 17:51   ` Valentin Schneider
2021-10-04 13:42     ` Frederic Weisbecker
2021-10-05 20:55       ` Paul E. McKenney
2021-09-29 22:10 ` [PATCH 09/11] rcu: Fix callbacks processing time limit retaining cond_resched() Frederic Weisbecker
2021-10-01 17:51   ` Valentin Schneider
2021-09-29 22:10 ` [PATCH 10/11] rcu: Apply callbacks processing time limit only on softirq Frederic Weisbecker
2021-10-01 17:51   ` Valentin Schneider
2021-10-04 13:47     ` Frederic Weisbecker
2021-10-06 15:12       ` Valentin Schneider
2021-10-07  0:18         ` Frederic Weisbecker
2021-09-29 22:10 ` [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Frederic Weisbecker
2021-09-30 15:37   ` Sebastian Andrzej Siewior [this message]
2021-10-11 12:11     ` Frederic Weisbecker
2021-10-01 17:47 ` [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes Valentin Schneider
2021-10-08 14:03   ` Valentin Schneider
2021-10-08 15:49     ` Paul E. McKenney
2021-10-06 15:13 ` Paul E. McKenney
2021-10-07  8:49   ` Sebastian Andrzej Siewior
2021-10-07 19:12     ` Paul E. McKenney
2021-10-11 14:51 [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes v2 Frederic Weisbecker
2021-10-11 14:51 ` [PATCH 11/11] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Frederic Weisbecker

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