On Thu, 2 Mar 2000, Andrea Arcangeli wrote:
> "In lowest priority mode, if a focus processor exists, it may
> accept the interrupt, regardless of its priority. A processor is
> said to be the focus of an interrupt if it is currently servicing
> that interrupt or if it has a pending request for that
> interrupt."
>
> Can a CPU have pending request for an interrupt and be running with irq
> locally disabled?
yes, the local APIC queues pending interrupts, and these pending requests
serve as a 'focus' for subsequent interrupts, just in case they happen. I
have not actually seen any big effect from this, but it does make sense
conceptually - if the IRQ rate is very high. Having said that, for
level-triggered IRQs this probably has no effect (because no new IRQs are
sent for a not yet acked in-service or pending IRQ), but if a
level-triggered IRQ holds up an edge-triggered IRQ then that
edge-triggered IRQ serves as a focus for subsequent IRQs. Should not be a
too common case though :-)
-- mingo
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