On Thu, 9 Mar 2000, Andrea Arcangeli wrote:
>
> >Each cpu has its own interrupt mask register, so the actual interrupt
> >handler needn't worry about communicating with other processors.
>
> Yes, but we definitely need the per irq-desc locking to avoid to run the
> irq handler on two CPUs at the same time.
Indeed. There's probably no way to avoid that lock, so one lock is a
minimum requirement. That's true even with interrupt controllers that
don't ever distribute the irq's the way you describe: we need _some_
synchronization with things like "disable_irq()", "request_irq()" and
"release_irq()", and a per-irqdescriptor spinlock is just the obvious
way to do it.
You could probably play games here and use lockless data structures and
other magic, but the complexity would probably obviate the gain.
Linus
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