[Tor-BSD] Slow network performance on virtualized OpenBSD 6.6

[Winter Paulson]

Hello all,

I've been running OpenBSD and FreeBSD bare metal tor exits for some
time. Now I have some speed issues with a virtualized OpenBSD node where
I only reach ~ 12.5 MB/s tor throughput.

The host is running Debian Buster, Intel X550T NICs and AMD EPYC 7xx1
processor and has 2 x 1 GBit/s uplink (not limited). The VM has 2 GB RAM
and 4 CPU cores allocated and the tor process is not limited atm by
single thread performance. Local unbound is doing DNS resolution (2
threads).

Running iperf3 to public servers (e. g. ping.online.net) resulted in
960 Mbit/s download and more than 120 Mbit/s upload (slow on ramping, so
there is probably much more available when testing to a private iperf3
server) while the tor server is running. So in principle there is more
bandwidth available.

I changed the network driver from virtio to e1000 and performance
increased around ~ 1.5 MB/s. I tried to disable hardware offloading but
couldn't find out how to do so in openbsd. Trying "ifconfig em0 -rxcsum
-txcsum -tso -lro" results in "bad value" for each of the parameters
(with virtio and e1000 driver). "ifconfig -m em0" is not available on
openbsd to show the (enabled) capabilities of the virtual NIC.

Does anyone know how to check if hardware offloading is active on a
virtualised openbsd and if applicable how to disable it? Also any other
tips on how to increase would be much appreciated!

Thanks a lot!

winter