linux-kernel - Re: [PATCH] clockevents: return error from tick_broadcast_oneshot_control if !GENERIC_CLOCKEVENTS

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Message-ID: <alpine.DEB.2.11.1506261437280.4037@nanos>
Date:	Fri, 26 Jun 2015 14:38:10 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
cc:	Sudeep Holla <sudeep.holla@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Suzuki Poulose <Suzuki.Poulose@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] clockevents: return error from tick_broadcast_oneshot_control
 if !GENERIC_CLOCKEVENTS_BROADCAST

On Fri, 26 Jun 2015, Preeti U Murthy wrote:
> On 06/26/2015 01:17 PM, Thomas Gleixner wrote:
> >  	if (state == TICK_BROADCAST_ENTER) {
> > +		/*
> > +		 * If the current CPU owns the hrtimer broadcast
> > +		 * mechanism, it cannot go deep idle and we do not add
> > +		 * the CPU to the broadcast mask. We don't have to go
> > +		 * through the EXIT path as the local timer is not
> > +		 * shutdown.
> > +		 */
> > +		ret = broadcast_needs_cpu(bc, cpu);
> > +
> > +		/*
> > +		 * If the hrtimer broadcast check tells us that the
> > +		 * cpu cannot go deep idle, or if the broadcast device
> > +		 * is in periodic mode, we just return.
> > +		 */
> > +		if (ret || tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
> > +			goto out;
> 
> The check on PERIODIC mode is good, but I don't see the point of moving
> broadcast_needs_cpu() up above. broadcast_shutdown_local() calls
> broadcast_needs_cpu() internally.
> 
> Besides, by jumping to 'out', we will miss programming the broadcast
> hrtimer in tick_broadcast_set_event() below, if the cpu happen to be the
> broadcast cpu(which is why it was not allowed to go to deep idle).

Hmm. Need to think a bit more about this convoluted maze ...
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