[Xen-devel] NR_PIRQS vs. NR_IRQS

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

I'm having some difficulty understanding why these two need to be
distinguished: Depending on the code location, an IRQ passed in from the
guest may be checked against NR_PIRQS (map_domain_pirq() as called
from PHYSDEVOP_alloc_irq_vector) or NR_IRQS (PHYSDEVOP_irq_status_query,
PHYSDEVOP_map_pirq), despite it having the same source.

Also, tying NR_IRQS to NR_VECTORS seems bogus - even with current
code I can't see why we shouldn't be able to support a higher NR_IRQS
without immediately doing the more involved code changes needed to
also grow NR_VECTORS. After all, NR_IRQS is directly tied to the number
of IO-APIC pins we can support - in order to support a device, its
cumulative pin number (being the irq) must be below NR_IRQS. But since
very likely not all pins are connected to devices, NR_VECTORS is much
less of a limiting factor.

Thanks, Jan


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