From: Steven Rostedt <rostedt@goodmis.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
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>
Subject: Re: sched: Reenable interrupts in do sched_yield()
Date: Tue, 20 Oct 2020 16:07:32 -0400 [thread overview]
Message-ID: <20201020160732.5f8fc24e@oasis.local.home> (raw)
In-Reply-To: <87o8kw93n4.fsf@nanos.tec.linutronix.de>
On Tue, 20 Oct 2020 20:02:55 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:
> On Tue, Oct 20 2020 at 11:38, Steven Rostedt wrote:
> > On Tue, 20 Oct 2020 16:46:55 +0200
> > Thomas Gleixner <tglx@linutronix.de> wrote:
> >
> >> - /*
> >> - * Since we are going to call schedule() anyway, there's
> >> - * no need to preempt or enable interrupts:
> >
> > I think the above comment still makes sense, just needs to be tweeked:
> >
> > /*
> > * Since we are going to call schedule() anyway, there's
> > * no need to allow preemption after releasing the rq lock.
> >> - */
> >
> > Especially, since we are now enabling interrupts, which is likely to
> > trigger a preemption.
>
> sched_preempt_enable_no_resched() still enables preemption. It just
> avoids the check. And it still allows preemption when an interrupt
> triggering preemption happens between sched_preempt_enable_no_resched()
> and __schedule() disabling preemption/interrupts.
>
> So no, your new variant is just differently bogus and misleading.
What I wrote wasn't exactly what I meant. What I meant to have:
/*
* Since we are going to call schedule() anyways, there's
* no need to do the preemption check when the rq_lock is released.
*/
That is, to document why we have the preempt_disable() before the unlock:
preempt_disable();
rq_unlock_irq(rq, &rf);
sched_preempt_enable_no_resched();
-- Steve
next prev parent reply other threads:[~2020-10-20 20:07 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 14:46 sched: Reenable interrupts in do sched_yield() Thomas Gleixner
2020-10-20 15:38 ` Steven Rostedt
2020-10-20 18:02 ` Thomas Gleixner
2020-10-20 20:07 ` Steven Rostedt [this message]
2020-10-21 7:27 ` Thomas Gleixner
2020-10-21 14:07 ` Steven Rostedt
2020-12-23 12:02 ` Qais Yousef
2020-10-29 10:51 ` [tip: sched/core] sched: Reenable interrupts in do_sched_yield() tip-bot2 for Thomas Gleixner
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