Re: PCI MSI questions

[Keir Fraser <keir.fraser@eu.citrix.com>]

On 24/7/08 08:02, "Jan Beulich" <jbeulich@novell.com> wrote:

> 1) There currently seems to be a hidden requirement of NR_PIRQS in the
> kernel needing to be no smaller than NR_IRQS in the hypervisor.
> Otherwise, the pirq returned from PHYSDEVOP_map_pirq may collide
> with the dynamic IRQs in the kernel or even be out of range altogether.
> Therefore I think that NR_PIRQS has to become a variable defaulting
> to 256 but getting initialized from a hypervisor reported value (perhaps
> in start_info, or else from a new (sub-)hypercall).

Or have the kernel remap the return value of map_pirq into its own PIRQ
namespace, and maintain appropriate translation info? Although, it'd be nice
to have dynamic NR_IRQS sizing anyway -- people who want to run lots of
domUs currently may have to recompile dom0 with more DYNIRQS.

> 4) The hypervisor option "msi_irq_enable" seems to be named pretty
> oddly - both the "irq" and the "enable" in the name are more or less
> redundant. So unless there's a reason for this long a name for an
> option that generally I would expect most people want to set (at
> least on bigger systems), I'd like to change it into "msi" or, if that's
> considered prone for ambiguity, "pci-msi". Also, are there any plans
> when to make have default be on rather than off?

Renaming sounds sensible. I admit I forgot it was turned off by default. I
guess at this point we should turn it on by default immediately after 3.3
has branched.

 -- Keir