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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: Wed, 21 Oct 2020 10:07:14 -0400	[thread overview]
Message-ID: <20201021100714.5ba25a96@gandalf.local.home> (raw)
In-Reply-To: <87h7qo6ntx.fsf@nanos.tec.linutronix.de>

On Wed, 21 Oct 2020 09:27:22 +0200
Thomas Gleixner <tglx@linutronix.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@linutronix.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

  reply	other threads:[~2020-10-21 14:07 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
2020-10-21  7:27       ` Thomas Gleixner
2020-10-21 14:07         ` Steven Rostedt [this message]
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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