linux-kernel - Re: [RFC PATCH v1 2/9] genirq: Support shared per_cpu

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Date:   Thu, 19 Oct 2017 16:08:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paul Burton <paul.burton@...tec.com>
cc:     Ralf Baechle <ralf@...ux-mips.org>, dianders@...omium.org,
        James Hogan <james.hogan@...tec.com>,
        Brian Norris <briannorris@...omium.org>,
        Jason Cooper <jason@...edaemon.net>, jeffy.chen@...k-chips.com,
        Marc Zyngier <marc.zyngier@....com>,
        linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
        tfiga@...omium.org
Subject: Re: [RFC PATCH v1 2/9] genirq: Support shared per_cpu_devid
 interrupts

On Tue, 26 Sep 2017, Thomas Gleixner wrote:
> On Mon, 25 Sep 2017, Thomas Gleixner wrote:
> 
> > On Thu, 7 Sep 2017, Paul Burton wrote:
> > > Up until now per_cpu_devid interrupts have not supported sharing. On
> > > MIPS we have some percpu interrupts which are shared in many systems -
> > > a single CPU interrupt line may be used to indicate a timer interrupt,
> > > performance counter interrupt or fast debug channel interrupt. We have
> > > up until now supported this with a series of hacks, wherein drivers call
> > > each other's interrupt handlers & our MIPS GIC irqchip driver includes a
> > > hack which configures the interrupt(s) for all CPUs. In order to allow
> > > this mess to be cleaned up, this patch introduces support for shared
> > > per_cpu_devid interrupts.
> > > 
> > > The major portion of this is supporting per_cpu_devid interrupts in
> > > __handle_irq_event_percpu() and then making use of this, via
> > > handle_irq_event_percpu(), from handler_percpu_devif_irq() to invoke the
> > > handler for all actions associated with the shared interrupt. This does
> > > have a few side effects worth noting:
> > > 
> > >  - per_cpu_devid interrupts will now add to the entropy pool via
> > >    add_interrupt_randomness(), where they previously did not.
> > > 
> > >  - per_cpu_devid interrupts will record timings when IRQS_TIMINGS is
> > >    set, via record_irq_time(), where they previously did not.
> > > 
> > >  - per_cpu_devid interrupts will handle an IRQ_WAKE_THREAD return from
> > >    their handlers to wake a thread, where they previously did not.
> > 
> > That's broken because it lacks the magic synchronization which is described
> > in the comment in __irq_wake_thread().
> 
> Aside of that to make that work at all would require per cpu threads and
> not a single systemwide thread.

also request_threaded_irq() will yell at you if you call it for a percpu
interrupt.

Care to rewrite the changelog and make that conditional:

 irqreturn_t __handle_irq_event_percpu(struct irq_desc *desc, unsigned int *flags)
 {
+	bool percpu = irq_settings_is_per_cpu_devid(desc);
 	irqreturn_t retval = IRQ_NONE;
 	unsigned int irq = desc->irq_data.irq;
 	struct irqaction *action;
@@ -142,9 +143,15 @@ irqreturn_t __handle_irq_event_percpu(st
 
 	for_each_action_of_desc(desc, action) {
 		irqreturn_t res;
+		void *dev_id;
+
+		if (!percpu))
+			dev_id = action->dev_id;
+		else
+			dev_id = raw_cpu_ptr(action->percpu_dev_id);
 
Thanks,

	tglx