[libvirt-users] Strange behavior of QoS

[Gao Yongwei]

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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