Re: In kernel PIC support: kernel patch

Gregory Haskins
2007-06-21T15:17:53Z

On Thu, 2007-06-21 at 22:28 +0800, Dong, Eddie wrote:
>
> > I suppose, but it somewhat defeats the purpose IMO. Every pin in the
> > 8259 that gets tickled implicitly means an IOAPIC pin was tickled
> > also. Do we really want to go to userspace for that? Essentially
>
> User space can handle this, go to IOAPIC first and then decide to go to
> in kernel PIC or not. Here the assumption is that an irq line is either
> serviced
> by PIC or IOAPIC, it will never be serviced by both.
>
> So no back to user space.

Yeah, I suppose if we adopt that optimization from Xen/Qemu that is
true. The design in my head is trying to emulate the actual signal path
in hardware so it gets dispatched to both models. I suppose you can get
away with a shortcut like that here (though I don't really love the
idea ;).

I think it comes down to the decision, like you said. If we go with
IOAPIC in the kernel, just route to both like I am thinking. If we
leave it in userspace, optimize the context switch away for performance
reasons.

-Greg