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

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Message-ID: <alpine.DEB.2.11.1510011625000.4500@nanos>
Date:	Thu, 1 Oct 2015 16:31:18 +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, 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.
 
> Alternative I could implement ->irq_set_affinity() in the GPIO driver in
> question [1] which always calls directly parent chip's ->irq_set_affinity()
> but I'm not sure if that is allowed.

I rather prefer to avoid that.

Thanks,

	tglx
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