Re: In kernel PIC support: kernel patch

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





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