Re: Predictable and consistent net interface naming in guests

On Thu, Dec 8, 2022 at 5:44 PM Laine Stump <laine(a)redhat.com&gt; wrote: > > On 12/8/22 11:15 AM, Julia Suvorova wrote: > > 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. > > Are you saying you can add an acpi-index to a device plugged into a pxb, > that index will be recognized (and used to name the device), but it will > still do native hotplug? nope, acpi-index won't work on pxb hierarchy, it works only PCI tree hanging off main host bridge. > > That sounds okay to me, since it ticks all the functional marks > (hotplug, consistent device names, NUMA-aware). It's possible there are > some things I'm misunderstanding or haven't thought of though... > > > > > >>> 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. > >>>> > > >