Very slow and inconsistent internal network speed (between, VM's on the same host) for FreeBSD 11.0+ as guest on, XCP-ng/XenServer

[Eugene Grosbein]

25.06.2019 18:55, Christian M wrote:

> Please note the
> extremely uneven throughput for test 2 below. It's almost like the
> throughput increased when running tcpdump simultaneously.

Generally this indicates broken "hardware" offload for some features
like txcsum/rxcsum/vlan_hwcsum/vlan_hwtagging etc.

Some of them may be automatically disabled while interface is put in promiscuous mode
by running tcpdump and enabled back after tcpdump terminated.

You should look at "options" line in the output of ifconfig for the interface
and manually disable offloads (look for ifconfig(8) manual for details).
They retry tests without tcpdump running.