Packets dropped by virtual NICs

Hi all, I want to use tc qdisc settings in a network coposed of several qemu VMs, connected through bridges and tap interfaces. I generate traffic with a spirent. Everything is fine when the scheduling discipline is not installed but when I run the command to set taprio queues traffic on the VM's NIC the traffic is dropped, i can send max 1mbps. I think that there is something missing in the virtual NIC configuration or setup. With ethtool i can see that queues are configured. I've also noticed the BQL equals to 0, that is different than the physical machine (BQL=18600) where everything works correctly. I've read that it could be because NIC drivers do not support that setting. Do you have any suggestions? Thanks you all Silvia