Re: Predictable and consistent net interface naming in guests

On Thu, Nov 3, 2022 at 9:26 AM Amnon Ilan <ailan(a)redhat.com&gt; wrote: > > > > 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? Why would you need to add acpi hotplug on 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) Native hotplug works on pxb as is, without disabling acpi hotplug.

>> 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. >>>