linux-kernel - Re: [PATCH 1/3] idle: add support for tasks that inject idle

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Date:   Mon, 14 Nov 2016 17:22:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Chen, Yu C" <yu.c.chen@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH 1/3] idle: add support for tasks that inject idle

On Mon, Nov 14, 2016 at 08:20:28AM -0800, Jacob Pan wrote:
> On Mon, 14 Nov 2016 16:01:19 +0100
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Wed, Nov 09, 2016 at 11:05:10AM -0800, Jacob Pan wrote:
> > > +void play_idle()
> > > +{
> > > +	/*
> > > +	 * Only FIFO tasks can disable the tick since they don't
> > > need the forced
> > > +	 * preemption.
> > > +	 */
> > > +	WARN_ON_ONCE(current->policy != SCHED_FIFO);
> > > +	WARN_ON_ONCE(current->nr_cpus_allowed != 1);
> > > +	WARN_ON_ONCE(!(current->flags & PF_KTHREAD));
> > > +	WARN_ON_ONCE(!(current->flags & PF_NO_SETAFFINITY));
> > > +	rcu_sleep_check();
> > > +
> > > +	preempt_disable();
> > > +	current->flags |= PF_IDLE;
> > > +	do_idle();
> > > +	current->flags &= ~PF_IDLE;
> > > +
> > > +	preempt_fold_need_resched();
> > > +	preempt_enable();
> > > +}
> > > +EXPORT_SYMBOL_GPL(play_idle);  
> > 
> > Hurm.. didn't this initially also include the setup of the timer and
> > take an timeout argument?
> 
> right, the initial version has a timeout and
> 	init_timer_on_stack(timer);
> 
> I thought since this play_idle timer is likely to expire instead of
> being canceled, so I switched to hrtimer by caller. We don't have an on
> stack hrtimer, right? or Should we consider adding one?

hrtimer_init_on_stack() exists.