Re: PCI, ACPI, IRQ, IOAPIC: reroute PCI interrupt to legacy boot interrupt equivalent

Ingo Molnar
2009-01-13T01:47:58Z

* Jon Masters <jcm@redhat.com> wrote:

> On Mon, 2009-01-12 at 15:36 -0800, Eric W. Biederman wrote:
>
> > This hardware behavior is not specific to boot interrupts or Intel.
>
> It's not specific to Intel, but it is a specific compatibility behavior.
>
> > Is this case really so interesting and compelling that we want to
> > fight through and figure what we need to do to make this work reliably
> > on every x86 chipset?
>
> How else do you propose implementing IRQ handling in e.g. the RT kernel?
> We get a hardware interrupt, we can't FastEOI, we can't process
> synchronously, we can't do all of those things you might expect.
> Implementing RT requires that we delay handling of the IRQ until
> arbitrarily later in the future when we get around to it.

a number of mainline drivers also mask/unmask irqs from within the IRQ
handler. It's not particularly smart in a native driver, but can happen -
and if we get an active line after that point (and this can happen because
the driver is active), we are in trouble.

Ingo