On Tue, 4 Oct 2016 15:59:11 +0100 "Daniel P. Berrange" <berra...@redhat.com> wrote:
> On Mon, Sep 05, 2016 at 06:24:48PM +0200, Laszlo Ersek wrote: > > On 09/01/16 15:22, Marcel Apfelbaum wrote: > > > +2.3 PCI only hierarchy > > > +====================== > > > +Legacy PCI devices can be plugged into pcie.0 as Integrated Devices or > > > +into DMI-PCI bridge. PCI-PCI bridges can be plugged into DMI-PCI bridges > > > +and can be nested until a depth of 6-7. DMI-BRIDGES should be plugged > > > +only into pcie.0 bus. > > > + > > > + pcie.0 bus > > > + ---------------------------------------------- > > > + | | > > > + ----------- ------------------ > > > + | PCI Dev | | DMI-PCI BRIDGE | > > > + ---------- ------------------ > > > + | | > > > + ----------- ------------------ > > > + | PCI Dev | | PCI-PCI Bridge | > > > + ----------- ------------------ > > > + | | > > > + ----------- ----------- > > > + | PCI Dev | | PCI Dev | > > > + ----------- ----------- > > > > Works for me, but I would again elaborate a little bit on keeping the > > hierarchy flat. > > > > First, in order to preserve compatibility with libvirt's current > > behavior, let's not plug a PCI device directly in to the DMI-PCI bridge, > > even if that's possible otherwise. Let's just say > > > > - there should be at most one DMI-PCI bridge (if a legacy PCI hierarchy > > is required), > > Why do you suggest this ? If the guest has multiple NUMA nodes > and you're creating a PXB for each NUMA node, then it looks valid > to want to have a DMI-PCI bridge attached to each PXB, so you can > have legacy PCI devices on each NUMA node, instead of putting them > all on the PCI bridge without NUMA affinity. Seems like this is one of those "generic" vs "specific" device issues. We use the DMI-to-PCI bridge as if it were a PCIe-to-PCI bridge, but DMI is actually an Intel proprietary interface, the bridge just has the same software interface as a PCI bridge. So while you can use it as a generic PCIe-to-PCI bridge, it's at least going to make me cringe every time. > > - only PCI-PCI bridges should be plugged into the DMI-PCI bridge, > > What's the rational for that, as opposed to plugging devices directly > into the DMI-PCI bridge which seems to work ? IIRC, something about hotplug, but from a PCI perspective it doesn't make any sense to me either. Same with the restriction from using slot 0 on PCI bridges, there's no basis for that except on the root bus. Thanks, Alex
