linux-kernel - Re: [RFC PATCH 2/2] sched: idle: IRQ based next prediction for idle period

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Message-ID: <alpine.DEB.2.11.1601121523070.3575@nanos>
Date:	Tue, 12 Jan 2016 15:26:21 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
cc:	peterz@...radead.org, rafael@...nel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, nicolas.pitre@...aro.org,
	vincent.guittot@...aro.org
Subject: Re: [RFC PATCH 2/2] sched: idle: IRQ based next prediction for idle
 period

On Tue, 12 Jan 2016, Daniel Lezcano wrote:
> On 01/12/2016 02:42 PM, Thomas Gleixner wrote:
> > On Tue, 12 Jan 2016, Daniel Lezcano wrote:
> > > On 01/08/2016 04:43 PM, Thomas Gleixner wrote:
> > > > > +	/*
> > > > > +	 * Register the setup/free irq callbacks, so new interrupt or
> > > > > +	 * freed interrupt will update their tracking.
> > > > > +	 */
> > > > > +	ret = register_irq_timings(&irqt_ops);
> > > > > +	if (ret) {
> > > > > +		pr_err("Failed to register timings ops\n");
> > > > > +		return ret;
> > > > > +	}
> > > > 
> > > > So that stuff is installed unconditionally. Is it used unconditionally
> > > > as
> > > > well?
> > > 
> > > Sorry, I am not sure to understand your question. If the kernel is
> > > compiled
> > > with CONFIG_CPU_IDLE_GOV_SCHED=y, this code is enabled and use the irq
> > > timings. The condition comes from the compilation option.
> > 
> > The question is whether the option also activates that thing or is there
> > still
> > some /sys/whatever/idlegov magic where you can (de)select it.
> 
> Yes, in the next patches of the series I did not send, we can switch to the
> cpuidle's governor framework or idle-sched. I will look at how to disable it
> when switching to the cpuidle's governors.

You better implement the switching part in the cpuidle core first, i.e. proper
callbacks when a governor is switched in/out. Then make use of this switcheroo
right away. Doing it the other way round is just wrong.

Thanks,

	tglx