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From: Frederic Weisbecker <frederic@kernel.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Uladzislau Rezki <urezki@gmail.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 10/11] rcu: Apply callbacks processing time limit only on softirq
Date: Mon, 4 Oct 2021 15:47:48 +0200	[thread overview]
Message-ID: <20211004134748.GD273854@lothringen> (raw)
In-Reply-To: <874ka0my57.mognet@arm.com>

On Fri, Oct 01, 2021 at 06:51:32PM +0100, Valentin Schneider wrote:
> On 30/09/21 00:10, Frederic Weisbecker wrote:
> > Time limit only makes sense when callbacks are serviced in softirq mode
> > because:
> >
> > _ In case we need to get back to the scheduler,
> >   cond_resched_tasks_rcu_qs() is called after each callback.
> >
> > _ In case some other softirq vector needs the CPU, the call to
> >   local_bh_enable() before cond_resched_tasks_rcu_qs() takes care about
> >   them via a call to do_softirq().
> >
> > _ The time spent on other tasks after scheduling out, or on softirqs
> >   processing, is spuriously accounted to the time limit.
> >
> 
> That wasn't the case before ("rcu: Fix callbacks processing time limit
> retaining cond_resched()")

But if cond_resched_tasks_rcu_qs() was called and then on the next iteration
tlimit is checked, the time spent scheduling out is included, right?

Thanks.

> , though under PREEMPT_RT that *was* true (since
> bh-off remains preemptible). So I'd say that's a change we want.
> 
> > Therefore, make sure the time limit only applies to softirq mode.
> >
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > Cc: Valentin Schneider <valentin.schneider@arm.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> > Cc: Josh Triplett <josh@joshtriplett.org>
> > Cc: Joel Fernandes <joel@joelfernandes.org>
> > Cc: Boqun Feng <boqun.feng@gmail.com>
> > Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
> > Cc: Uladzislau Rezki <urezki@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> 
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>

  reply	other threads:[~2021-10-04 13:47 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 [this message]
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
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 10/11] rcu: Apply callbacks processing time limit only on softirq Frederic Weisbecker

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