using driver 149 and NetKVM this is quiet eash to replicate. Just install iperf3 in the vm and run it as iperf server
Turn the windows firewall off (or allow port 5201 tcp)
Then on another machine (i just used the proxmox host) again install iperf3 and run
Code:
iperf3 -c 192.0.2.2 -w 130k -P 4 -t 60
It will choke and stop sending data pretty quickly
I tried turning all forms of offloading off in the windows network interface properties but this made no difference.
Gong back to 141 (stable) seems to have fixed it for me.
Note that you have to go to device manager, right click on the device to get properties then uninstall the driver. I then went to the mounted iso for 141 found the NetKVM/2k16/amd64 folder, right clicked on netkvm.inf and clicked install. Then went back to device manager, clicked action, then "scan for hardware change". The VirtiIO Ethernet Adapter reappeared, i then checked its properties to confirm it was running 141. then did a complete shutdown and start up to make sure that the qemu/kvm process was fresh. Note that the network adapters advanced settings are default (ie offloading are all on)
This seems to have fixed it for me
I will say that 141 is much lower throughput than 149 (2Gbit/s versus 10Gbit/s) - however it continues to work which is much higher throughput than seizing up.