On Thu, 3 Nov 2022 00:13:16 +0200 Amnon Ilan <ailan@redhat.com> wrote:

On Wed, Nov 2, 2022 at 6:47 PM Laine Stump <laine@redhat.com> wrote:

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On Wed, 2 Nov 2022 15:20:39 +0000 Daniel P. Berrangé <berrange@redhat.com> wrote:

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On Wed, Nov 02, 2022 at 04:08:43PM +0100, Igor Mammedov wrote:

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On Wed, 2 Nov 2022 10:43:10 -0400 Laine Stump <laine@redhat.com> wrote:

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On 11/1/22 7:46 AM, Igor Mammedov wrote: > On Mon, 31 Oct 2022 14:48:54 +0000 > Daniel P. Berrangé <berrange@redhat.com> wrote: > >> On Mon, Oct 31, 2022 at 04:32:27PM +0200, Edward Haas wrote: >>> Hi Igor and Laine, >>> >>> I would like to revive a 2 years old discussion [1] about consistent network >>> interfaces in the guest. >>> >>> That discussion mentioned that a guest PCI address may change in two cases: >>> - The PCI topology changes. >>> - The machine type changes. >>> >>> Usually, the machine type is not expected to change, especially if one >>> wants to allow migrations between nodes. >>> I would hope to argue this should not be problematic in practice, because >>> guest images would be made per a specific machine type. >>> >>> Regarding the PCI topology, I am not sure I understand what changes >>> need to occur to the domxml for a defined guest PCI address to change. >>> The only think that I can think of is a scenario where hotplug/unplug is >>> used, >>> but even then I would expect existing devices to preserve their PCI address >>> and the plug/unplug device to have a reserved address managed by

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>>> acting on it (the management system). >>> >>> Could you please help clarify in which scenarios the PCI topology can cause >>> a mess to the naming of interfaces in the guest? >>> >>> Are there any plans to add the acpi_index support? >> >> This was implemented a year & a half ago >> >> https://libvirt.org/formatdomain.html#network-interfaces >> >> though due to QEMU limitations this only works for the old >> i440fx chipset, not Q35 yet. > > Q35 should work partially too. In its case acpi-index support > is limited to hotplug enabled root-ports and PCIe-PCI bridges. > One also has to enable ACPI PCI hotplug (it's enled by default > on recent machine types) for it to work (i.e.it's not supported > in native PCIe hotplug mode). > > So if mgmt can put nics on root-ports/bridges, then acpi-index > should just work on Q35 as well.

With only a few exceptions (e.g. the first ich9 audio device, which is placed directly on the root bus at 00:1B.0 because that is where the ich9 audio device is located on actual Q35 hardware), libvirt will automatically put all PCI devices (including network interfaces) on a pcie-root-port.

After seeing reports that "acpi index doesn't work with Q35 machinetypes" I just assumed that was correct and didn't try it. But after seeing the "should work partially" statement above, I tried it just now and an <interface> of a Q35 guest that had its PCI address auto-assigned by libvirt (and so was placed on a pcie-root-port)m and had <acpi index='4'/> was given the name "eno4". So what exactly is it that *doesn't* work?

From QEMU side: acpi-index requires: 1. acpi pci hotplug enabled (which is default on relatively new q35 machine types) 2. hotpluggble pci bus (root-port, various pci bridges) 3. NIC can be cold or hotplugged, guest should pick up acpi-index of

On 11/2/22 11:58 AM, Igor Mammedov wrote: the one the device

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currently plugged into slot what doesn't work: 1. device attached to host-bridge directly (work in progress) (q35) 2. devices attached to any PXB port and any hierarchy hanging of it

(there are not plans to make it work)

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(q35, pc)

I'd say this is still a relatively important, as the PXBs are needed to create a NUMA placement aware topology for guests, and I'd say it is undesirable to loose acpi-index if a guest is updated to be NUMA aware, or if a guest image can be deployed in either normal or NUMA aware setups. ...

How big of a project would it be to enable ACPI-indexing/hotplug with PXB? Since native PCI was improved, we can still compromise on switching to native-PCI-hotplug when PXB is required (and no fixed indexing)

My guesstimate would be it's not terribly difficult. Maybe we could even marry native hotplug & acpi-index after the later is decoupled from ACPI PCI hotplug as much as possible.

Thanks, Amnon

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Anyway, it sounds like (*within the confines of how libvirt constructs the PCI topology*) we actually have functional parity of acpi-index between 440fx and Q35.