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

[Roger Pau Monné]

On Tue, Jun 25, 2019 at 01:55:40PM +0200, Christian M wrote:
> I've made two tests while running tcpdump on the xcp-ng host. I'm not at
> all qualified to interpret the .pcap files from tcpdump, but I've put them
> on Google Drive and linked them below the two tests. Perhaps someone more
> qualified could have a look for anything useful in there. Please note the
> extremely uneven throughput for test 2 below. It's almost like the
> throughput increased when running tcpdump simultaneously.
> 
> Host: XCP-ng 7.6.0
> Network: Private Network on host, not connected to any PIF.
> VM1: 12.0-RELEASE (1 VIF, 172.31.16.125)
> VM2: 12.0-RELEASE (1 VIF, 172.31.15.126)
> 
> On the host I listen with tcpdump on the VIF for VM1 in both tests.
> 
> VM1 as client:
> 
> On XCP-ng: tcpdump -i vif42.0 -s 0 -w xcp-ng-vm1-client.pcap

Can you check the capabilities of vif42.0? (ie: whether csum
offloading is actually disabled on the host?)

> xcp-ng-vm1-client.pcap (80M):
> https://drive.google.com/open?id=1eR3fetvKRz3vFSXCxDKuJYFrQ3wLqjrU
> On VM1: iperf3 -c 172.31.16.126
> On VM2: iperf3 -s

I've taken a look at the dump and the checksum is wrong (or maybe
missing) for all? packets.

Packets with source 172.31.16.125 all have the TCP checksum set to
0x7f80 and all packets with source 172.31.16.125 have the TCP checksum
set to 0x7960.

FTR, can you also paste the ifconfig output of each interface before
running iperf?

Thanks, Roger.