linux-kernel - Re: [PATCH v2] sched: Have do_idle() call __schedule() without enabling preemption

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Date:   Wed, 12 Apr 2017 20:40:00 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] sched: Have do_idle() call __schedule() without 
 enabling preemption

On Wed, 12 Apr 2017 16:48:59 -0700
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> I don't understand why schedule_idle() needs a loop given that
> schedule_preempt_disabled() doesn't have one, but other than

But it does:

void __sched schedule_preempt_disabled(void)
{
	sched_preempt_enable_no_resched();
	schedule();
	preempt_disable();
}

Where we have:

asmlinkage __visible void __sched schedule(void)
{
	struct task_struct *tsk = current;

	sched_submit_work(tsk);
	do {
		preempt_disable();
		__schedule(false);
		sched_preempt_enable_no_resched();
	} while (need_resched());
}

Which makes:

void __sched schedule_preempt_disabled(void)
{
	struct task_struct *tsk  = current;

	scehdule_preempt_enable_no_resched();
	sched_submit_work(tsk);
	do {
		preempt_disable();
		__schedule(false);
		schedule_preempt_enable_no_resched();
	} while (need_resched());
	preempt_disable();
}

My schedule_idle() is simply schedule_preempt_disabled() without the
change in preemption and no call to sched_submit_work().


> that, for whatever it is worth, it looks good to me.
> 

Does this mean I can change the Cc: to Acked-by: ?

-- Steve


> > +void __sched schedule_idle(void)
> > +{
> > +	do {
> > +		__schedule(false);
> > +	} while (need_resched());
> > +}
> > +