[libvirt-users] Strange results with QoS definition

[Michal Privoznik]

On 27.09.2013 11:03, Patrick Herzfeld wrote:
> Hi
> 
> I'm currenty testing network QoS implementations stumbled upon quite
> strange results when using QoS definitions inside the virtdomain xml.
> 
> I'm testing bandwidth from a virtdomain towards a hardware server
> connected to the same switch, both connected to gigabit ports. Iperf
> tells me the bandwidth is around 939 Mbit/s.
> 
> I added this to my virtdomains xml:
> <bandwidth>
>      <inbound average='1280'/>
>      <outbound average='1280'/>
> </bandwidth>
> This should limit the bandwidth to around 10 megabit/s 1280 kilobytes/s,
> however i get only around 5.14 Mbits/sec...
> 
> Has anyone an idea what causes this difference?
> 
> I already checked the applied qdisc & class:
> 
> root at testvirt-patrick:~ # tc qdisc sh dev vnet1
> qdisc htb 1: root refcnt 2 r2q 10 default 1 direct_packets_stat 0
> qdisc ingress ffff: parent ffff:fff1 ----------------

SFQ is missing. So I assume you're using and older libvirt (pre 1.0.1).
There has been some bugs prior that release ...

> root at testvirt-patrick:~ # tc class sh dev vnet1
> class htb 1:1 root prio 0 rate 10240Kbit ceil 10240Kbit burst 1598b
> cburst 1598b

.. notably in setting these burst and cburst values.

Try to update and the problem should get resolved.

Michal