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SubjectRe: 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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