Re: Predictable and consistent net interface naming in guests

On Thu, Nov 3, 2022 at 12:13 AM Amnon Ilan <ailan(a)redhat.com&gt; wrote: > > > > On Wed, Nov 2, 2022 at 6:47 PM Laine Stump <laine(a)redhat.com&gt; wrote: >> >> On 11/2/22 11:58 AM, Igor Mammedov wrote: >> > On Wed, 2 Nov 2022 15:20:39 +0000 >> > Daniel P. Berrangé <berrange(a)redhat.com&gt; wrote: >> > >> >> On Wed, Nov 02, 2022 at 04:08:43PM +0100, Igor Mammedov wrote: >> >>> On Wed, 2 Nov 2022 10:43:10 -0400 >> >>> Laine Stump <laine(a)redhat.com&gt; wrote: >> >>> >> >>>> On 11/1/22 7:46 AM, Igor Mammedov wrote: >> >>>>> On Mon, 31 Oct 2022 14:48:54 +0000 >> >>>>> Daniel P. Berrangé <berrange(a)redhat.com&gt; 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 the one >> >>>>>>> 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 the device >> >>> 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) >> >>> (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. >> > >> > it's not only Q35 but also PC. >> > We basically do not generate ACPI hierarchy for PXBs at all, >> > so neither ACPI hotplug nor depended acpi-index would work. >> > It's been so for many years and no one have asked to enable >> > ACPI hotplug on them so far. >> >> I'm guessing (based on absolutely 0 information :-)) that there would be >> more demand for acpi-index (and the resulting predictable interface >> names) than for acpi hotplug for NUMA-aware setup. > > > My guess is similar, but it is still desirable to have both (i.e. support ACPI-indexing/hotplug with Numa-aware) > Adding @Peter Xu to check if our setups for SAP require NUMA-aware topology > > How big of a project would it be to enable ACPI-indexing/hotplug with PXB?

Adding +Julia Suvorova and +Tsirkin, Michael to help answer this question Thanks, Amnon > > Since native PCI was improved, we can still compromise on switching to native-PCI-hotplug when PXB is required (and no fixed indexing)

> Thanks, > Amnon > > >> >> >> 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. >>