From: Steven Rostedt <rostedt@goodmis.org>
To: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] sched: Prevent raising SCHED_SOFTIRQ when CPU is !active
Date: Tue, 15 Dec 2020 09:34:15 -0500 [thread overview]
Message-ID: <20201215093415.5b2898ef@gandalf.local.home> (raw)
In-Reply-To: <alpine.DEB.2.21.2012151449260.1448@somnus>
On Tue, 15 Dec 2020 15:23:39 +0100 (CET)
Anna-Maria Behnsen <anna-maria@linutronix.de> wrote:
> > > + /*
> > > + * Remove CPU from nohz.idle_cpus_mask to prevent participating in
> > > + * load balancing when not active
> > > + */
> > > + nohz_balance_exit_idle(rq);
> > > +
> > > set_cpu_active(cpu, false);
> > > /*
> > > * We've cleared cpu_active_mask, wait for all preempt-disabled and RCU
> >
> > OK, so we must clear the state before !active, because getting an
> > interrupt/softirq after would trigger the badness. And we're guaranteed
> > nothing blocks between them to re-set it.
>
> As far as I understood, it is not a problem whether the delete is before or
> after !active. When it is deleted after, the remote CPU will return in
> kick_ilb() because cpu is not idle, because it is running the hotplug
> thread.
I was thinking that disabling it after may also cause some badness. Even if
it does not, I think there's no harm in clearing it just before setting cpu
active to false. And I find that the safer option.
-- Steve
next prev parent reply other threads:[~2020-12-15 14:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-15 10:44 [PATCH] sched: Prevent raising SCHED_SOFTIRQ when CPU is !active Anna-Maria Behnsen
2020-12-15 11:18 ` Peter Zijlstra
2020-12-15 14:23 ` Anna-Maria Behnsen
2020-12-15 14:34 ` Steven Rostedt [this message]
2020-12-15 15:05 ` Peter Zijlstra
2020-12-15 17:52 ` Thomas Gleixner
2020-12-16 8:19 ` Peter Zijlstra
2020-12-16 10:10 ` Thomas Gleixner
2020-12-15 14:24 ` Steven Rostedt
2021-01-14 11:29 ` [tip: sched/core] " tip-bot2 for Anna-Maria Behnsen
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