High Latency with Intel i226-v NIC on Proxmox Passthrough to VM

[Roman]

Hello everyone,

I'm having a tough time with my home network configuration and could use some help troubleshooting a high-latency issue. I'm experiencing significant latency on my Intel i226-v PCIe NIC when passing it through to an OPNsense VM on Proxmox. Here’s my setup and what I've tried so far:

Setup Details:​

• Host: Lenovo M920q (i7, 16GB RAM), Proxmox (latest version, fully updated)
• NIC: Intel i226-v (PCIe card with 4 ports, purchased from AliExpress, link)
• Guest OS: OPNsense VM (fully updated)
• Use Case: Dedicated PCI passthrough of the NIC to the OPNsense VM

The Intel i226-V model was chosen for its perfect compatibility with the M720q and M920q cases, using this riser and bracket kit: link.

Issue:​

When pinging the OPNsense VM from the LAN, I’m seeing high latency (ping > 40ms) within the LAN. However, when I remove the NIC from the VM and test it directly on the Proxmox host, latency is normal (under 1ms).

Troubleshooting Steps Taken:​

1. OPNsense Configuration: Disabled all hardware offloading settings in OPNsense.
2. BIOS Settings on Lenovo: Tested various configurations, including disabling ASPM.
3. VM Configurations in Proxmox: Switched between Q35 and i440fx with different versions.
4. PCI Passthrough Configurations: Tried different options, including All Functions=1 and PCI-Express=1.
5. Kernel Boot Parameters in Proxmox: Tested multiple configurations, including:
   "quiet pci=assign-busses intel_iommu=on iommu=pt pcie_acs_override=downstream,multifunction pcie_port_pm=off pcie_aspm.policy=performance disable_idle_d3=1 acpi=off"
6. Kernel Downgrade: Downgraded to proxmox-kernel-6.2.16-20-pve.
7. Fresh OPNsense Installation: Tested with a clean OPNsense setup (only LAN and WAN configured).
8. Alternative OS: Installed Ubuntu VM with passthrough on the same NIC (same latency issue as with OPNsense).
9. Second Proxmox Node: Moved the OPNsense VM to another Lenovo M920q node with a different BIOS version (2019 and 2024), moving the NIC as well.

The problem only appears when the NIC is passed through to a VM, which makes me suspect it’s a software or configuration issue with QEMU PCI passthrough. Despite the numerous configurations and kernel tweaks I’ve tried, I haven’t been able to identify the root cause.

Has anyone else experienced similar issues, and are there any other steps I could take to debug or resolve this problem? Any help or guidance from the community would be greatly appreciated!

Thanks in advance!