Score:0

libvirt/KVM 10Gb-capable network interface without virtio

in flag

Is there a way to set up a 10Gb-capable virtual ethernet port in a guest VM (RHEL) without using virtio ?

I have to put some kind of RHEL7 in a guest VM but the kernel used in there has UDP fragmentation bugs when using virtio ethernet devices. The problems don't appear with the e1000 device (but then I'm capped at 1Gb/s), and no amount of futzing around settings can unbreak this virtio bug (and I can't upgrade the guest kernel).

Is there another way with virsh/libvirt than declaring a virtio device (e.g.):

<interface type="bridge">
  <mac address="00:00:32:32:b0:32"/>
  <source bridge="bridge_5"/>
  <target dev="vnet24"/>
  <model type="virtio"/>
  <driver name="vhost"/>
  <alias name="net0"/>
  <address type="pci" domain="0x0000" bus="0x00" slot="0x03" function="0x0"/>
</interface>

That would be able to send/receive 10Gb/s traffic ?

The host server has 2 x 10GbE (BCM57416) ethernet controlers, if it can help (can it ?)...

John Mahowald avatar
cn flag
Which virtio bug? My searches are only finding noise about the removal of UDP Fragmentation Offload from RHEL 8 kernels, and some old issue about UDP checksums and dhcpd.
Touisteur EmporteUneVache avatar
in flag
With UDP offload enabled I can see the pcap packets sent through without fragmentation although all interfaces are MTU 9000. Disabling all offloads (guest, host, everywhere) makes the guest VM send fragmented UDP packets but the first fragment has a wrong size field... I haven't located the specific bug in any bug DB but a more recent guest kernel doesn't show the problem. I can't seem to work around this (and I can't upgrade this guest), so I wanted to try something else than e1000 and virtio but that could still hit 10Gb.
John Mahowald avatar
cn flag
Please edit your question to add the kernel versions in question, and which are working versus not. And, IPv4 or IPv6?
I sit in a Tesla and translated this thread with Ai:

mangohost

Post an answer

Most people don’t grasp that asking a lot of questions unlocks learning and improves interpersonal bonding. In Alison’s studies, for example, though people could accurately recall how many questions had been asked in their conversations, they didn’t intuit the link between questions and liking. Across four studies, in which participants were engaged in conversations themselves or read transcripts of others’ conversations, people tended not to realize that question asking would influence—or had influenced—the level of amity between the conversationalists.