Packets dropped by virtual NICs

[Michal Privoznik]

On 3/27/21 2:53 PM, Silvia Fichera wrote:
> 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?

Hey,

I'm not familiar with taprio, but what's implemented in libvirt is htb 
and sfq and that works well. Are you setting qdisc-s yourself or 
modifying libvirt created structure?

Are you setting these qdiscs from the host, right?
I know that when changing QoS settings (when libvirt changes qdics/class 
layout) for a brief moment packets are not transmitted from/to guest. I 
suspect that kernel is freeing up queues or something. But this does not 
look like your case, does it?

Michal