I am experiencing very poor performance on a recently installed OPNsense version 25.1 VM in a Debian/KVM hosted environment. All the normally disabled offloading has been checked.
I have taken to troubleshooting the issue by using SCP from the OPNsense VM to/from various local and remote targets. Secure copies outbound perform fine in all cases. Secure copies inbound are exceedingly slow and packet capture reveals "TCP Previous segment not captured/TCP Retransmission" any time data must traverse the physical switch. Inbound from a source running on the same host works fine.
Here is the ifconfig from FreeBSD:
vtnet0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> metric 0 mtu 1500
description: Outside (wan)
options=80028<VLAN_MTU,JUMBO_MTU,LINKSTATE>
ether 52:54:00:44:b6:4b
inet <IP> netmask 0xfffffff0 broadcast <gatewayIP>
inet6 fe80::5054:ff:fe44:b64b%vtnet0 prefixlen 64 scopeid 0x1
media: Ethernet autoselect (10Gbase-T <full-duplex>)
status: active
nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
and relevant info from the KVM side:
root@kvm2:~# ip a s vnet122
135: vnet122: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master outside state UNKNOWN group default qlen 1000
link/ether fe:54:00:44:b6:4b brd ff:ff:ff:ff:ff:ff
inet6 fe80::fc54:ff:fe44:b64b/64 scope link
valid_lft forever preferred_lft forever
root@kvm2:~# ip a s outside
4: outside: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
link/ether 4e:bb:da:ba:6a:f8 brd ff:ff:ff:ff:ff:ff
inet6 fe80::4cbb:daff:feba:6af8/64 scope link
valid_lft forever preferred_lft forever
root@kvm2:~# ip a s enp2s0f1np1
3: enp2s0f1np1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master outside state UP group default qlen 1000
link/ether 9c:6b:00:99:c4:2e brd ff:ff:ff:ff:ff:ff
root@kvm2:~# ethtool -I vnet122
Settings for vnet122:
Supported ports: [ ]
Supported link modes: Not reported
Supported pause frame use: No
Supports auto-negotiation: No
Supported FEC modes: Not reported
Advertised link modes: Not reported
Advertised pause frame use: No
Advertised auto-negotiation: No
Advertised FEC modes: Not reported
Speed: 10Mb/s
Duplex: Full
Auto-negotiation: off
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
MDI-X: Unknown
Current message level: 0x00000000 (0)
Link detected: yes
Did you read this (https://forum.opnsense.org/index.php?topic=44159.0)? Especially the bits about network "hardware"?