linux-kernel - Re: [PATCH v3 3/4] irq: Allow multiple clients to register for irq affinity notification

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Date:	Fri, 17 Oct 2014 09:29:50 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Lina Iyer <lina.iyer@...aro.org>
cc:	khilman@...aro.org, ulf.hansson@...aro.org,
	linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, rjw@...ysocki.net,
	daniel.lezcano@...aro.org
Subject: Re: [PATCH v3 3/4] irq: Allow multiple clients to register for irq
 affinity notification

On Fri, 10 Oct 2014, Lina Iyer wrote:
> On Wed, Oct 08 2014 at 09:03 -0600, Thomas Gleixner wrote:
> > On Thu, 25 Sep 2014, Lina Iyer wrote:
> > > > How would a general "keep track of the targets of all interrupts in
> > > > the system" mechanism make use of this?
> > > Sorry, I do not understand your question.
> > > PM QoS is only interested in the IRQs specified in the QoS request. If
> > > there are no requests that need to be associated with an IRQ, then PM
> > > QoS will not register for an affinity change notification.
> > 
> > Right, and I really hate the whole per irq notifier. It's a rats nest
> > of life time issues and other problems.
> > 
> > It also does not tell you whether an irq is disabled, reenabled or
> > removed, which will change the qos constraints as well unless you
> > plaster all drivers with updates to qos for those cases.
> > 
> > So what about adding a qos field to irq_data itself, have a function
> > to update it and let the irq core keep track of the per cpu irq
> > relevant qos constraints and provide an evaluation function or a
> > notifier for the PM/idle code?
> 
> If that isnt intrusive in the IRQ core, then we can make it work for PM
> QoS. The issue that I am concerned is that, it might result in back and
> forth between IRQ and PM QoS frameworks. If that doesnt happen, then we
> are good with this approach.

I can't tell that upfront, but I think it's worth to explore it.

Thanks,

	tglx
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