linux-kernel - Re: CPU hotplug and chained interrupts on x86

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Message-ID: <alpine.DEB.2.11.1510012343370.4500@nanos>
Date:	Thu, 1 Oct 2015 23:45:23 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
cc:	Jiang Liu <jiang.liu@...ux.intel.com>, linux-kernel@...r.kernel.org
Subject: Re: CPU hotplug and chained interrupts on x86

On Thu, 1 Oct 2015, Thomas Gleixner wrote:
> On Thu, 1 Oct 2015, Mika Westerberg wrote:
> > Now if I plug/unplug the card I may get few interrupts to CPU0 but rest
> > of the interrupts never happen. Probably because IO-APIC forwards them
> > to the lowest priority CPU which is offline at this point.
> > 
> > There is following check in fixup_irqs():
> > 
> > 	if (!irq_has_action(irq) || irqd_is_per_cpu(data) ||
> > 	    cpumask_subset(affinity, cpu_online_mask)) {
> > 		raw_spin_unlock(&desc->lock);
> > 		continue;
> > 	}   
> > 
> > If an interrupt is requested by a driver it will force new affinity and
> > everything works fine. However if the interrupt is chained (it does not
> > have ->action) this is skipped and the current affinity remains.
> > 
> > We could detect here if the interrupt is chained but there seems to be
> > no easy way to determine it currently so we would need to add a new flag
> > to desc->status_use_accessors that gets set in __irq_do_set_handler()
> > when is_chained is 1.
> 
> Either there or in irq_data. Need to look at it in detail.

desc->status_use_accessors is the place where this wants to go.

Thanks,

	tglx
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