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: Thu, 7 Oct 2021 02:18:43 +0200 [thread overview]
Message-ID: <20211007001843.GA304532@lothringen> (raw)
In-Reply-To: <87ilyakx0z.mognet@arm.com>
On Wed, Oct 06, 2021 at 04:12:12PM +0100, Valentin Schneider wrote:
> On 04/10/21 15:47, Frederic Weisbecker wrote:
> > 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?
> >
>
> if tlimit was set, then that branch would either continue or break; both
> cases would have skipped over the cond_resched_tasks_rcu_qs() (which the
> aforementioned patch addresses).
Duh, right indeed. I need to clarify the changelog.
Thanks!
next prev parent reply other threads:[~2021-10-07 0:18 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 [this message]
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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