libvirt users - Dec 2012 - Strange behavior of QoS

Hi,
I'm having some weird problem with the setup of the QoS on a bridged
network.

As the docs states, outbound/inbound average speed should be expressed in KBps
(KBytes per second) but in order to get a maximum speed of 10Mbps (megabits per
second) surprising enough I have to use 2560 on the guest (not 1280 as
expected).
Using 1280 units I get a speed og 5Mbps.

I'm aware of peak and burst parameters but even with them I'm seeing the
same (long-term) behavior.

Here follows my configuration. 

Thank you in advance for any help you can provide.



Domain definition (relevant part only)

virsh # dumpxml mydomain
<domain type='kvm' id='45'>
 [...]
 <devices>
   [...]
   <interface type='network'>
     <mac address='52:54:00:xx:xx:xx'/>
     <source network='br909'/>
     <target dev='vnet43'/>
     <model type='virtio'/>
     <bandwidth>
       <inbound average='2560'/>
       <outbound average='2560'/>
     </bandwidth>
     <alias name='net0'/>
     <address type='pci' domain='0x0000' bus='0x00'
slot='0x03' function='0x0'/>
   </interface>
   [...]
 </devices>
</domain>


The network definition:
virsh # net-dumpxml br909
<network>
 <name>br909</name>
 <uuid>07319380-2025-cdcc-924a-149cd0370b56</uuid>
 <forward mode='bridge'/>
 <bridge name='br909' />
</network>


And iperf result (client and server are on the same vlan and they are running on
the same host)

[  5] local xx.xx.xx.xx port 5001 connected with xx.xx.xx.yy port 18396
[  5]  0.0-30.1 sec  35.4 MBytes  9.87 Mbits/sec


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2012/12/3 Davide Guerri <d.guerri at unidata.it>
> Hi,
> I'm having some weird problem with the setup of the QoS on a bridged
> network.
>
> As the docs states, outbound/inbound average speed should be expressed in
> KBps (KBytes per second) but in order to get a maximum speed of 10Mbps
> (megabits per second) surprising enough I have to use 2560 on the guest
> (not 1280 as expected).
> Using 1280 units I get a speed og 5Mbps.
>
> I'm aware of peak and burst parameters but even with them I'm
seeing the
> same (long-term) behavior.
>
> Here follows my configuration.
>
> Thank you in advance for any help you can provide.
>
>
>
> Domain definition (relevant part only)
>
> virsh # dumpxml mydomain
> <domain type='kvm' id='45'>
>  [...]
>  <devices>
>    [...]
>    <interface type='network'>
>      <mac address='52:54:00:xx:xx:xx'/>
>      <source network='br909'/>
>      <target dev='vnet43'/>
>      <model type='virtio'/>
>      <bandwidth>
>        <inbound average='2560'/>
>        <outbound average='2560'/>
>      </bandwidth>
>      <alias name='net0'/>
>      <address type='pci' domain='0x0000'
bus='0x00' slot='0x03'
> function='0x0'/>
>    </interface>
>    [...]
>  </devices>
> </domain>
>
>
> The network definition:
> virsh # net-dumpxml br909
> <network>
>  <name>br909</name>
>  <uuid>07319380-2025-cdcc-924a-149cd0370b56</uuid>
>  <forward mode='bridge'/>
>  <bridge name='br909' />
> </network>
>
>
> And iperf result (client and server are on the same vlan and they are
> running on the same host)
>
> [  5] local xx.xx.xx.xx port 5001 connected with xx.xx.xx.yy port 18396
> [  5]  0.0-30.1 sec  35.4 MBytes  9.87 Mbits/sec
>
provide your os version and libvirt version plz.
and use the following command to check the tc mtu size:
   tc filter list dev vnet0 root
if the mtu size in the output is not 64kb,then you must update your libvirt
to 0.9.11 or later.
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