I see that the current queue discipline is set to
pfifo_fast, whilst tcp congestion control is set to
sysctl net | grep -E "(qdisc|congestion)" net.core.default_qdisc = pfifo_fast net.ipv4.tcp_congestion_control = cubic
May be, same settings should to be set on the edge, the worker (host), and not just the guest (app) but I am not familiar with
virt_io to know if there are more knobs to tune.