linux-kernel - Re: sched: Reenable interrupts in do sched

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Message-ID: <20201021100714.5ba25a96@gandalf.local.home>
Date:   Wed, 21 Oct 2020 10:07:14 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: sched: Reenable interrupts in do sched_yield()

On Wed, 21 Oct 2020 09:27:22 +0200
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Tue, Oct 20 2020 at 16:07, Steven Rostedt wrote:
> > On Tue, 20 Oct 2020 20:02:55 +0200
> > Thomas Gleixner <tglx@...utronix.de> wrote:
> > 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:  
> 
> which is pretty obvious, but I let Peter decide on that.

To us maybe, but I like to have comments that explain why things are done to
average people. ;-)

If I go to another kernel developer outside the core kernel, would they know
why there's a preempt_disable() there?


 	preempt_disable();
	rq_unlock_irq(rq, &rf);
 	sched_preempt_enable_no_resched();
 
 	schedule();


Not everyone knows that the rq_unlock_irq() would trigger a schedule if an
interrupt happened as soon as irqs were enabled again and need_resched was
set.

-- Steve