On Tue, 29 Feb 2000, Linus Torvalds wrote:
>> - IRQ_PENDING: If I interpret the comment there correctly, the check is
>> only necessary for faulty SMP hardware?
>
>It's only necessary for hardware that doesn't work the way we want it to
>work.
More precisely it's necessary only with edge triggered irqs. That's why in
the alpha port I added underlined check to improve performance:
for (;;) {
handle_IRQ_event(irq, regs, action);
spin_lock(&irq_controller_lock);
if (!(desc->status & IRQ_PENDING)
|| (desc->status & IRQ_LEVEL))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
break;
desc->status &= ~IRQ_PENDING;
spin_unlock(&irq_controller_lock);
}
On IA32 setting the status to IRQ_LEVEL during initialization is not
necesary because IA32 can enforce by design that with level triggered irq
that the same irq can't recurse in any way or run at the same time in
parallel cpus. But the above makes much difference on alpha since it
ensures we don't run the irq->handler a second time for no good reason.
Andrea
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