Re: [Xen-devel] [PATCH][HVM] fix PCI interrupt routing via ACPI

["Dave Lively" <dave.lively@xxxxxxxxx>]

On 10/16/06, Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> wrote:
>  On 16/10/06 15:51, "Dave Lively" <dave.lively@xxxxxxxxx> wrote:
>
>
> What about PIC mode support?  OSes expecting just a PIC may
>  rely on being able to choose the 4 PCI IRQs.  But I don't know
>  this for sure.  In fact, I remember Win2003 with the ACPI PIC HAL
>  was successfully working around this problem (by leaving the PCI
>  IRQ assignments unchanged), though it complained in the event
>  log.  I'm not sure whether we can rely on this or not ...
>
>  I think it's unlikely they'd rely on it. If we don't care about the PIC-mode 
> limitation
> we could keep the PIIX3 emulation
Are you proposing we use the (current) PIIX3 interrupt routing emulation for
PIC mode guests, and simply hide the interrupt routing functionality for APIC
mode?  That would certainly address my concerns about PIC mode (but note
neither of us is convinced my concerns here are legitimate).

> (but I'm not sure that most OSes would bother to switch to APIC mode if they 
> have only
Mostly I see SMP kernels using it on uniprocessor configs.

> one processor). But bothering to try to emulate better PCI-ISA bridge hardware 
> feels like
> wasted effort if we can sidestep the entire problem.
I'm all for sidestepping the problem when that works.  But I worry
that the requirement
of supporting PIC mode means we need this general functionality (i.e.,
PCI interrupt
routing) anyway.  Since there will be no performance advantage in
hiding this functionality
in APIC mode, perhaps we're better off just leaving it there.

Dave

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel