Re: [Qemu-devel] [RFC 3/3] acpi-build: allocate mcfg for multiple host bridges

[Alex Williamson]

On Wed, 23 May 2018 00:44:22 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Tue, May 22, 2018 at 03:36:59PM -0600, Alex Williamson wrote:
> > On Tue, 22 May 2018 23:58:30 +0300
> > "Michael S. Tsirkin" <address@hidden> wrote:   
> > >
> > > It's not hard to think of a use-case where >256 devices
> > > are helpful, for example a nested virt scenario where
> > > each device is passed on to a different nested guest.
> > >
> > > But I think the main feature this is needed for is numa modeling.
> > > Guests seem to assume a numa node per PCI root, ergo we need more PCI
> > > roots.  
> > 
> > But even if we have NUMA affinity per PCI host bridge, a PCI host
> > bridge does not necessarily imply a new PCIe domain.  
> 
> What are you calling a PCIe domain?

Domain/segment

0000:00:00.0
^^^^ This

Isn't that the only reason we'd need a new MCFG section and the reason
we're limited to 256 buses?  Thanks,

Alex