Re: [libvirt] [PATCH v3 11/18] qemu: assign virtio devices to PCIe slot when appropriate

On Thu, 2016-10-06 at 10:34 -0400, Laine Stump wrote: >>> + <video> >>> + <model type='virtio' heads='1' primary='yes'/> >>> + <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/> >> >> I was initially baffled by this, because I expected it to >> be assigned to one of the available pcie-root-ports just >> like all the other virtio devices. >> >> However, according to qemuDomainValidateDevicePCISlotsQ35() >> this is intentional, so I guess we're good :) > > Actually, you bring up an interesting point in light of the "Should PCIe > devices ever be placed directly on pcie-root?" debate on qemu-devel (I > think it was in the thread about the PCI topology document that Marcel > is writing). We currently always put the primary video device at 00:1 > just because "we always have", and it has the nice side effect of > eliminating the need for legacy-PCI controllers. But in this one case > the device is PCIe - to follow Marcel's recommendation of putting only > legacy devices on pcie-root, we should be putting the virtio video > device on a root-port. > > As I recall, Marcel and Alex were the most vocal on this subject, so I'm > Cc'ing them, with this bit of context - this patch auto-assigns the > addresses for virtio devices to be on Express ports rather than legacy > slots when appropriate, but there is a bit of Q35-specific code that > overrides any of that and always places the primary video device at > 00:01.0 - should we still do that for the primary video if it's virtio? > Or should we put it behind a root-port? I don't think we ever got a reply... Bump? :)